Guide to Decorative Concrete · hardscapes. Using color and texture introduced concrete as a landscape feature in addition to its functionality. An example is flatwork textured and

ACI 310R-13

Guide to Decorative Concrete

Reported by ACI Committee 310

Copyright American Concrete Institute

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First PrintingDecember 2013


Copyright by the American Concrete Institute, Farmington Hills, MI. All rights reserved. This material may not be reproduced or copied, in whole or part, in any printed, mechanical, electronic, film, or other distribution and storage media, without the written consent of ACI.

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This guide describes techniques for imparting aesthetic finishes to concrete flatwork, of which many can be combined for unique effects. The designer/engineer will acquire detailed, practical guidance for achieving aesthetic effects using proven techniques. Recommendations are made for the production of cast-in-place decorative concrete flatwork, decorative stains, and overlays. In addition to attention to the specified materials, mixture designs, concrete placement, curing, protection, sealing, and other treat-ments, this guide also considers the effects of these treatments on the overall aesthetics of the facility.

Keywords: aggregates; cementitious materials; decorative overlays; dry-shake hardeners; dry-shake release agents; embedment; embossing; engraving; etching; flatwork; imprinting; inlays; pavements; polishing; sealants; stains; stamping; tooling.

CONTENTS

CHAPTER 1—INTRODUCTION AND SCOPE, p. 21.1—Introduction, p. 21.2—Scope, p. 3

CHAPTER 2—DEFINITIONS, p. 3

CHAPTER 3—GENERAL AND DESIGN CONSIDERATIONS, p. 4

3.1—General, p. 43.2—Process development, p. 43.3—Substrate preparation, p. 53.4—Jointing, p. 53.5—Joint filling, p. 63.6—Proper installation and quality control, p. 63.7—Climate, p. 73.8—Curing, p. 73.9—Sealers, p. 83.10—Safety, p. 103.11—Reinforcement, p. 103.12—Sustainability, p. 10

CHAPTER 4—PLASTIC CONCRETE COLOR TECHNIQUES, p. 10

4.1—General, p. 104.2—Integral color, p. 104.3—Color shake-on hardeners, p. 124.4—Exposed aggregate, p. 134.5—Advantages, p. 154.6—Disadvantages, p. 154.7—Special procedures and tools, p. 154.8—Required products, p. 154.9—Safety, p. 154.10—Maintenance, p. 15

ACI 310R-13


Reported by ACI Committee 310

Larry Rowland, Chair

Lance BoyerClark Branum

Walter B. BurnsTerry C. Collins

Daniel P. DorfmuellerJames A. FarnyRoy E. Harvey

David E. HoytAllyn C. Luke

Scott C. MetzgerMichael E. Murray

Dionne OjedaJoe A. Reardon

Todd A. Scharich

Michael S. SmithNicholas J. Sorrentino

Cori E. SuttonJames Vermillion

Consulting membersDoug Bannister

Larry E. GoodRobert P. HarrisHarry P. Moats

Joseph V. NasvikFrank Piccolo

1

ACI Committee Reports, Guides, and Commentaries are intended for guidance in planning, designing, executing, and inspecting construction. This document is intended for the use of individuals who are competent to evaluate the significance and limitations of its content and recommendations and who will accept responsibility for the application of the material it contains. The American Concrete Institute disclaims any and all responsibility for the stated principles. The Institute shall not be liable for any loss or damage arising therefrom.

Reference to this document shall not be made in contract documents. If items found in this document are desired by the Architect/Engineer to be a part of the contract documents, they shall be restated in mandatory language for incorporation by the Architect/Engineer.

ACI 310R-13 was adopted and published December 2013.Copyright © 2013, American Concrete InstituteAll rights reserved including rights of reproduction and use in any form or by any

means, including the making of copies by any photo process, or by electronic or mechanical device, printed, written, or oral, or recording for sound or visual reproduc-tion or for use in any knowledge or retrieval system or device, unless permission in writing is obtained from the copyright proprietors.

ACI Committee 310 wishes to extend special acknowledgements to the following individuals for their contribution to the development of this guide: M. S. Smith, N. Blackburn, J. Strieder, and A. Werner.




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CHAPTER 5—PLASTIC CONCRETE TEXTURING AND PATTERNING TECHNIQUES, p. 15

5.1—Texturing: embossing, imprinting, stenciling, and stamping, p. 15

5.2—Stamping, p. 175.3—Texture and pattern rollers, p. 175.4—Stencils (paper templates), p. 195.5—Object impressing, p. 205.6—Texturing with standard tooling, p. 20

CHAPTER 6—POST-PLACEMENT COLORING TECHNIQUES, p. 21

6.1—General, p. 216.2—Reactive stains, p. 246.3—Concrete dyes, p. 286.4—Acid etching, p. 28

CHAPTER 7—POST-PLACEMENT TEXTURING AND PATTERNING TECHNIQUES, p. 29

7.1—General, p. 297.2—Ground and polished concrete, p. 307.3—Sandblast stenciling (abrasive blast stenciling), p. 377.4—Engraved concrete, p. 397.5—Decorative saw-cutting (scoring), p. 40

CHAPTER 8—DECORATIVE OVERLAYS AND REPAIR METHODS, p. 41

8.1—General, p. 418.2—Special procedures and tools, p. 428.3—Required products, p. 438.4—Application, p. 438.5—Touch-ups and post-repair aesthetic treatments, p. 44

CHAPTER 9—MAINTENANCE, p. 449.1—General, p. 449.2—Coatings and sealers, p. 449.3—Stained concrete, p. 449.4—Color hardened and densified concrete, p. 449.5—Maintenance plan and closeout documentation, p. 45

CHAPTER 10—REFERENCES, p. 45Cited references, p. 45

CHAPTER 1—INTRODUCTION AND SCOPE

1.1—IntroductionDecorative concrete has been in existence since approxi-

mately 70 AD, when concrete was used for defining affluent or important areas of living space in communal cultures. Early examples of this type of adornment are the streets and paving throughout the city of Pompeii near Naples, Italy. Early deco-rative concrete used colored aggregates and varying shapes or natural materials embedded in concrete paving.

Traditionally, concrete has been specified more for its functional characteristics than as an enhancement to the aesthetics of the structure. Landscape architects were leaders in using concrete flatwork to enhance the visual appeal of hardscapes. Using color and texture introduced concrete as a

landscape feature in addition to its functionality. An example is flatwork textured and colored to replicate the look of slate, brick, or natural stone as shown in Fig. 1.1a and 1.1b.

The use of decorative concrete has been well received and considered as an alternative to other building materials for durable, versatile, and economical finishes. More designers are creating greater aesthetic appeal in projects by using one or more combinations of special concrete placement techniques including integral concrete colors, color hard-eners, chemical stains, pigments and dyes, surface texturing, jointing, exposed aggregate, surface embossing, polishing,

Fig. 1.1a—Stamped, colored concrete with slate and brick patterns in landscape setting (courtesy of Decorative Concrete Resources).

Fig. 1.1b—Concrete slab enhances design aesthetic with mimic of stone slab (courtesy of L. M. Scofield Company).

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2 GUIDE TO DECORATIVE CONCRETE (ACI 310R-13)




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and the use of sealants and coatings. The combinations of techniques and mediums described in this guide are exclu-sive; they cannot be replicated by any other durable medium.

1.2—ScopeThis guide describes several techniques for imparting

aesthetic finishes to concrete, many of which can be combined for unique effects (Fig. 1.2). The guide provides detailed practical guidance for achieving aesthetic effects using proven techniques, both within and beyond the context of ACI 302.1R, which also governs these concrete elements.

Recommendations for the production of cast-in-place decorative concrete, stains, and overlays are presented. In addition to attention to specified materials, mixture designs, concrete placement, curing, protection, sealing, and other treatments, consideration of the effects of these treatments on the overall aesthetics of the structure is also addressed.

CHAPTER 2—DEFINITIONS“2013 ACI Concrete Terminology” provides a compre-

hensive list of definitions that are available online at: http://terminology.concrete.org. The definitions provided here complement that source.

acid (or chemical) stain—see reactive stain.color hardener—similar to traditional one-component

hardeners, having additional constituent materials formu-lated to color the concrete surface.

concrete dye—colorant for concrete that is applied to the concrete while it is in solution and results in a stained appearance; concrete dyes do not produce color via chemical reaction—they are usually a synthetic organic compound and can degrade when exposed to light or alkalinity.

crack chaser—rotary tool using a v-shaped diamond blade to enlarge cracks in concrete to facilitate repair. The v-shape of the blade assists the operator in following the curves of the crack so as to not cause unnecessary damage to the piece being prepared for repair.

decorative aggregate—specially selected aggregates chosen for their artistic contribution to the project; examples of materials used as decorative aggregate include colored stone, intrinsically valuable gathered stone, semiprecious stone, or colored glass.

decorative overlay—mixture of cementitious materials installed over an existing concrete substrate; they can be integrally colored, stenciled, or used for artistic enhance-ment post-placement.densifier—combination of silicate and water-based

compounds that react in the surface of the concrete to produce additional calcium silicate hydrate (C-S-H); sili-cates are combined with carrier compounds, most commonly sodium-, potassium-, or lithium-based to aid the process. Some products also contain siliconate.

embossing—creating a raised print or reverse replication of an object in the concrete surface.

engraving—cutting with a mechanical rotary or impact tool to texture a concrete surface product.

etch—textured surface produced by cutting with a mechanical impact tool or by chemical etching by use of acid.

grinding—intentional removal of a visually apparent amount of surface without consideration of gloss.

integral color—pigment that changes the color of the paste portion of the concrete mixture to produce a color change throughout the hardened concrete matrix.

microtopping—bonded cementitious overlay usually 1/8 to 3/16 in. (3 to 5 mm) in thickness; when installed over an existing concrete substrate post-placement, it can be inte-grally colored, stenciled, or used for artistic enhancement.

needle scaler—reciprocal impact tool that uses single or multiple thin rods to strike a surface.

polished concrete—post-placement architectural finish or texturing technique where concrete undergoes sequential mechanical abrasion resulting in a glossy surface with clarity ranging from matte to high gloss, depending on which point in the sequence the abrasion is ended; does not achieve gloss solely by the use of surface coatings. The complete process commonly includes chemical densification for increased strength and reduction of absorption.

polished overlay—bonded cementitious overlay 3/8 to 1 in. (10 to 25 mm) in depth cast over an existing concrete substrate designed to accept diamond abrading for a polished concrete appearance.

reactive stain—reactive solution of one or more metal salts stabilized by acid that produces coloration in a concrete substrate by neutralization of acid followed by precipitation of metal hydroxides or oxides.

stain(v)— use of a chemical stain or a concrete dye to change the color of the concrete surface that can be a penetrant or a low build coating that does not appreciably change the concrete’s texture; some acid stains can etch the concrete’s surface and can alter the texture.

stamping—process of applying a surface pattern to deco-rative concrete by using impact pressure to emboss texture, patterns, or faux joints into the surface of plastic concrete; usually providing a pattern of simulated natural materials

Fig. 1.2—Cast-in-place decorative concrete combining treatments during and post placement to achieve aesthetic effects (courtesy of Concrete Mystique Engraving).


GUIDE TO DECORATIVE CONCRETE (ACI 310R-13) 3




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such as brick, slate, tile, or stone using metal, soft or rigid plastic imprinting tools, or natural objects; also used to create a raised print or reverse replication of an object in the concrete surface.

stencil patterned concrete—texture created by use of preprinted pattern stencils or free form using alternate texturing materials.

surface release agent—temporary powder or liquid, usually pigmented, that is applied to plastic concrete surface immediately prior to imprinting or texturing that performs as a bond breaker between texturing tools and the concrete surface.

surface split—plastic shrinkage crack usually 0.005 to 0.060 in. (0.13 to 1.52 mm) wide and less than 1 in. (25 mm) in length appearing on top surface; normally near a joint or corner of imprinted surface.

weeding—process of removing portions of a stencil to allow decorative treatment or protection of specific areas to produce a desired pattern of contrasting color and or texture.

CHAPTER 3—GENERAL AND DESIGN CONSIDERATIONS

3.1—GeneralDecorative concrete is a durable building media providing

artistic choices and flexibility for the designer. Combina-tions of techniques (3.2) offer variations for adaptability and sustainability unmatched by other building materials.

3.2—Process developmentAlthough concrete is one of the most popular and versatile

construction materials, it has not always been known for its beauty. Creative and technical improvements in the concrete industry have resulted in better quality concrete and led to techniques that allow the contractor to manipulate concrete to resemble materials such as brick, slate, marble, granite, or other decorative stone. These techniques have been used to produce unique visual effects not possible with other mate-rials. Aesthetic effects can be added to concrete so that it combines with the structural landscape to produce a pleasant structure admired by all. As more color palettes, texturing systems, and post-placement processes become available, more owners are considering the addition of decorative concrete elements to their projects (Fig. 3.2).

Decorative concrete is subject to cracking and scaling common to all concrete construction when proper construc-tion and maintenance procedures are not followed. Properly designed concrete mixtures and joints and proper installa-tion procedures will mitigate many unwanted imperfections. Feature strips incorporated into a design can help avoid mismatched patterns and break up pattern fields into easily managed areas. Contractors installing decorative concrete should be experienced and possess the expert knowledge and skills necessary to work with it. Requiring contractors use ACI-certified flatwork finishers and or decorative flat-work finishers should ensure that the quality is consistently high.

3.2.1 Communication—A critical element among all participants of a project is to ensure the design intent of the owner, architect/engineer, or both, is achieved. Job-site meetings and mockups are helpful and allow those involved to share information and discuss their expectations, limita-tions, questions, and concerns (Fig. 3.2.1).

Some designers/engineers incorporate decorative designs and coloration into the structure; care should be taken to ensure tolerance requirements for the structural installation are consistent with those of the final decorative finishes. Where multiple contractors are responsible for end results of two distinctly different building mediums, tolerance incompatibility between phases of the work will dictate additional work or preparation by one of the contractors. Although similar materials and trades are needed to install the concrete, different levels of knowledge, care, and plan-ning are required. Issues that arise that can compromise achieving the intended design should be addressed with the designer/engineer and those involved, and an alternate solu-tion or plan formulated.

3.2.2 Sample panels—Just as historical data and trial batches demonstrate a material supplier’s ability to produce concrete suitable for a given project, sample panels demonstrate a contractor’s ability to produce the required decorative effects. Sample panels are typically small enough to be portable and are often used as a tangible exhibit of a contractor’s work. They give the owner and or architect/engineer a first look at what is achievable for a given application or process.

Fig. 3.2—Decorative concrete used to create visual effects not possible with other materials (courtesy of L. M. Scofield Company).






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Sample panels should use materials readily available for the project and be prepared under conditions similar to those anticipated during production. Once the sample panel appearance and mixture are approved, the procedures and methods used by the contractor to produce the panel should be incorporated into the project specification or be given precedence for the production quality controls associated with that portion of the project.

In-place work that has been in use for at least 2 years can serve as a practical sample, provided that the placement conditions and maintenance are properly documented. Color and durability are the most important variables affected by production and post-production elements. Weather condi-tions, deicing, and wear and tear due to traffic and snow or ice removal affect coloring over the first few years of service.

3.2.3 Mockup panels—A properly constructed mockup panel could be the single most useful component when establishing expectations for a project, especially when incorporating treatments affected by job-site conditions such as topical application of reactive stain or dye.

Mockup panels can give the architect/engineer, owner, and contractor an accurate example of the finished floor before construction begins. Adjustments in the methods or products can be made easier during the mockup phase than during the project. The mockup panel(s) should be sized to accurately display the surface treatment under consideration. Typical mockup panels range in size from 2 x 2 ft to 12 x 12 ft (0.6 x 0.6 m to 3.7 x 3.7 m). Some specifications or bid documents call for a specific size for the mockup panels and for the number of panels required. During a pre-job confer-

ence or bid meeting, participants should discuss the size and number of panels required as well as the scheduling conse-quences, construction costs, and financial responsibility for construction of the panels if any of these considerations are not clearly specified.

The type of mockup to be constructed will depend largely on the project requirements. A valid mockup should be produced with the same materials and methods as the finished work. Ideally, the mockup will be incorporated into the project in a noncritical room or isolated section of the work. This approach generates maximum flexibility and effi-ciency for the owner and installer.

Mockups are used as an achievable monument (referee panel) for prebid inspection by contractors, as a post-bid sample produced by the contractor awarded the project, or both, to verify the contractor can achieve the required appearance. Mockup panels should be kept in good condi-tion on site for reference by the installer, contractor, owner, or architect until project closeout. Mockup panels cast, cured, or aged differently from the main work will not have the same characteristics as the final work.

3.3—Substrate preparationThe substrate can be the ground below a slab, existing

plain concrete paving, or a structural slab designed to carry vehicle loads in addition to the dead load of the decorative concrete.

Properly compacted, slightly moistened, well-graded subgrades are important to the proper performance of most decorative installations. Conduct proper testing of the subgrade density and compaction to avoid unnecessary and costly corrections to work that has cracked or settled. Soil drainage or added layers of porous material are recommended in areas that experience freezing-and-thawing cycles. Moisture control is an important design consideration, as moisture transmission through colored concrete can cause efflorescence.

Subbase preparation is commonly overlooked in a specifi-cation but is critical to the slab aesthetics, quality, durability, and flatness. The subbase should be prepared in accordance with ACI 302.1R and should be free of any standing water or organic material. The subbase should be compacted properly and able to support the intended weight of the concrete and structure.

Soil reports should be obtained and referenced as required. The base should be graded evenly to provide consistent support for the concrete during placement, finishing, and curing. An uneven or inconsistent subbase can introduce additional stresses to the concrete during early stages of curing and strength gain. If these stresses exceed the tensile strength of the concrete during these stages, cracking will occur.

3.4—JointingJointing patterns and locations play an important role in

designing a functional, durable, and constructible instal-lation for decorative concrete. During the curing period, concrete tends to shrink proportionately in all directions, and selection of contraction and isolation joint location is crit-

Fig. 3.2.1—Good communication ensures the design intent is achieved (courtesy of L. M. Scofield Company).






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ical. Refer to ACI 360R for guidance, isolation joint place-ment details, and recommended contraction joint spacing. While square or rectangular patterns for contraction joints are most commonly used, other shapes can be employed, provided they do not result in isolated design elements that cannot shrink as a contiguous element.

Contraction joint cutting should be completed within 24 hours of initial concrete set to be fully effective. Early-entry dry-cut saw-cutting can be achieved without damaging the slab but requires supplemental joint protection during cutting.

Contraction joint layout and installation in decora-tive concrete should be done with consideration for the appearance of the overall pattern in the final work while maintaining appropriate joint spacing. Placement of joints under sill plates, using special feature strips, or incorpo-rating contraction joints into artistic work can help hide the control joint pattern. Specifiers should note that allowing the contractor control of joint placement can enhance the final appearance. The option of allowing contractor flexibility in joint placement should be considered and addressed in the design stage.

3.5—Joint fillingAll joints should be filled as recommended by ACI 360R.

A filler or sealant colored to complement the design should be used. The pattern joints can be grouted with a mixture of sand, cement, water, and coloring agent, or with manu-factured joint filler such as colored polyurea or semi-rigid epoxy, if desired. Care should be exercised to avoid staining patterned concrete surfaces with sealant or joint filler products.

Typically, joints are filled before most of the concrete shrinkage has occurred to avoid significant risk of joint opening and filler separation at the joint edge or within the filler. There is also the risk of joint filler or sealant pene-tration into the slab adjacent to the joint, creating a barrier that will not accept a reactive stain or dye. The timing of joint filling should be evaluated with respect to the advan-tages and disadvantages of early and late joint filling and the sealant or joint filler product used. Defer joint filling as long as possible to minimize shrinkage-related effects. If the project schedule requires that the joint be filled before most of the shrinkage has occurred, separation should be expected at the joint edge or within the joint filler itself. Joint filler separation due to slab shrinkage as a result of premature joint filling is not a joint filler material failure. When recom-mended by the filler manufacturer, slight openings of this type can be filled with additional filler.

3.6—Proper installation and quality controlContract documents typically require closer inspection

and fewer blemishes with decorative concrete than with normal concrete. Special consideration should be given to:

a) Materials and textures used during the design stage to ensure that the process and desired effect chosen will perform well in service in the climate where it will be used;

the use of color and topical sealers sometimes exaggerates minor flaws, which would be overlooked in plain concrete

b) Scheduling decorative work so that it is planned well in advance, allowing for adequate time to properly complete the production work according to the steps used in devel-oping an approved sample

c) Anticipating weather conditions during the scheduling process

d) Properly installing vapor retarders to avoid efflores-cence, which is particularly problematic on colored concrete because it is more visible than on uncolored concrete

Properly installing the slab is critical to the final appear-ance and performance of the finished product. Refer to ACI 318, ACI 301, and ACI 302.1R for guidance.

Maintain consistency in application methods, as it is para-mount to a uniform finish. For example, adding water to the surface of decorative concrete in any amount will change the finished appearance.

Size of placements should be based on experience, limiting the size to one the contractor can safely accomplish while producing a uniform finished surface. Placements should maintain proper grades and pitch to encourage proper water drainage flow off the slab or to drains. Protect surrounding surfaces so that fresh concrete from any new placement does not reach and damage previously finished sections.

Basic knowledge of concrete use and performance is of primary concern; installers should be carefully chosen based on previous performance. A recommended minimum requirement is that the crew leader should be certified as an ACI Decorative Concrete Flatwork Finisher.

3.6.1 Tolerances: F-Numbers—The F-Number system, which is the preferred standard specification for measuring the flatness and levelness of a concrete floor, is designated by ACI 117. The testing method is specified in ASTM E1155. This system includes two measurements:

a) FF—Floor flatness; a higher number indicates a flatter surface

b) FL—Floor levelness; a higher number indicates a more level surface

The FF number gives an indication of the bumpiness of the surface, and is evaluated for overlapping distances of 2 ft (600 mm) at 1 ft (300 mm) increments. The FL number relates directly to the pitch or tilt of a slab surface, and is evaluated for overlapping distances of 10 ft (3 m) at 1 ft (300 mm) increments.

It is difficult to evaluate the flatness and levelness of textured surfaces using traditional F-Number testing tech-niques. Profiles measured using this testing will confirm surface characteristics meet the project requirements. FF is an important characteristic for concrete intended to be polished. An overall minimum F-Number of FF-50 with a local minimum F-Number of FF-45 is desirable and mini-mizes aggregate exposure. Overall, an FF of less than 40 will result in unavoidable random aggregate exposure as the floor is flattened to polish. While there is no direct correla-tion between the older gap-under-a-straight-edge method of evaluating floor flatness, ACI 117-10 Sections 4.8.4 through 4.8.6 provide some guidance on the topic.







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ASTM E1155, which governs the evaluation of surfaces using the F-Number System, lists a number of acceptable measuring options. A properly trained and certified operator/technician can typically collect sufficient data to evaluate the F-Numbers of a surface in 60 to 90 minutes, depending on the size of the area. Most testing labs offer this service locally. Some testing labs offer dipstick rental for use by experienced contractors. All ASTM E1155 measurements for record should be performed by a technician certified in the use of the equipment required to collect the data.

3.6.2 Concrete mixture designs—Concrete mixture designs, also known as mixture proportions, are important to successful decorative concrete placement and execution. Mixture designs detail what fine and coarse aggregate; cement, supplemen-tary cementitious materials (SCMs), or both; pigments; and admixtures are combined with a specific amount of water to produce a workable mixture capable of achieving the desired structural and aesthetic goals of the project.

Concrete mixtures used previously with positive long-term results should be used as the basis for an initial trial batch design. In the absence of experience with a given mixture, field trial batches are necessary for the supplier to demonstrate their ability to deliver concrete that meets project requirements.

The use of clean, sound, hard aggregates that are free of any organic materials is recommended for decorative concrete applications. Do not use aggregate sources that contain more than 2 percent materials passing a No. 100 (150 mm) sieve. Select aggregates of the proper size for intended use meeting ASTM C33/C33M for the primary concrete mixture. Avoid gap-graded aggregates and optimize aggregate gradation for lower water demands. Do not use aggregate known to be reactive.

Suppliers offer a variety of seeded aggregates in different colors and sizes that are used for creating specific looks. Properties such as gradation, density, surface characteristics, and percentage of nonstandard or decorative aggregates that are used to replace normal aggregate should be known and considered in the custom mixture design process. Crushed glass should be coated, nonreactive, or both, to prevent the possibility of alkali-silica reaction (ASR) from occurring.

Concrete mixtures that achieve 3500 psi (24 MPa) 28-day compressive strength are generally considered normal for decorative concrete installations. Special attention should be given to the water-cementitious materials ratio (w/cm) to achieve dense, properly cured concrete that is less suscep-tible to cracking and problems such as efflorescence. Water-cementitious materials ratio ranges of 0.38 to 0.45 are workable and have proven to produce durable concrete for decorative installations. Lower w/cm values result in less water of convenience and generally produce more stable concrete color and increased concrete durability. Reduced water content can decrease porosity and bleed-water move-ment, which can increase moisture retention and reduce shrinkage.

SCMs can enhance the sustainability of the finished product and improve hardened properties of the concrete, such as its resistance to chemical attack, reduced porosity,

and improved strengths; however, they have an effect on concrete’s color and on a mixture’s plastic and hard-ened properties. These effects should be considered when deciding whether to include them in decorative concrete mixture designs. SCMs such as fly ash, slag cement, silica fume, metakaolin, ground reactive glass products, and other materials react with calcium hydroxide (Ca(OH)2) to form calcium-silicate hydrate (C-S-H). This reaction can nega-tively affect the effectiveness of decorative concrete mate-rials such as densifiers or reactive stains.

As with any concrete mixture, the workability of a given decorative concrete mixture will be affected by the amount of water in the mixture and the use of chemical admixtures. The workability of the mixture, often measured by slump, should be selected for the given project application and conditions. Chemical admixtures can be effectively used to minimize excess water or compensate for increased water demands resulting from the use of pigments or decorative aggregates, and they can also affect other plastic and hard-ened properties, such as set times and permeability. Calcium chloride and admixtures that contain chloride can yield unpredictable effects on concrete color and are, therefore, typically not recommended for use in decorative concrete mixtures.

3.7—ClimateDecorative concrete is used in all climate conditions and

is not limited to warm climates. Durability concerns require consideration of materials and the final service require-ments of the concrete. Concrete in warmer climates rarely experiences the abrasion of a snowplow or shovels. Warmer climates require temperature considerations for expansion and retaining moisture in the early-age concrete matrix. Refer to ACI 305R and ACI 318 for guidance on environ-mental considerations for concrete mixture designs. Climate also affects appropriate curing methods. Warmer arid climates often require more aggressive moisture-retention methods than cooler humid regions.

3.8—CuringThe quality and durability of a decorative concrete surface

can be greatly affected by curing procedures. Every effort should be made to maintain continuous moisture on the surfaces for the first 3 to 7 days to allow for the hydration of the cementitious materials. Loss of moisture from the surface zone of a concrete slab can cause cement hydration to slow or stop, leaving a weak surface that can be subject to scaling and loss of the finish surface by abrasion and other forms of damage. Using wind breaks, misting to increase humidity, applying evaporation retardant, and early morning or late evening placement help mitigate loss of surface moisture.

Special construction techniques involved with the instal-lation of decorative concrete can require the use of curing procedures that, while producing successful and durable decorative concrete installations, differ from the ones addressed in ACI 308.1. Some recommendations of ACI 308.1 interfere with production of the decorative effects that are the primary performance factor for decorative concrete.






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For example, membrane-forming curing compounds should be used with special care to avoid interference with subse-quent post-color treatments, penetrating sealers, and some polishing processes.

Decorative concrete curing procedures should be planned well in advance of application. If standard curing methods as outlined in ACI 308.1 cannot be followed, then the deco-rative concrete contractor should discuss planned curing practices at the preconstruction or preplacement meeting and be prepared to submit a plan outlining the curing proce-dures that will be followed. All required materials, such as curing blankets, fogging equipment, or surface release agents should be on the job site and ready to use when the appointed curing window opens. The contractor crew should take steps to prevent surface drying.

Curing techniques required for decorative concrete appli-cations, including stamping, trowel finish, float finish, colored floors, or floors expected to receive post-placement texturing or coloring, are critically dependent on anticipated weather conditions during and 24 hours after the initial installation. Improper choices of techniques can have detrimental effects on the final finish of the decorative concrete. If construc-tion schedules allow, concrete placements should be avoided during periods of low humidity, wind, and hot weather, as these conditions increase the rate of bleed-water evapora-tion. When possible, schedule decorative concrete place-ment at times best for the decorative concrete performance.

Some techniques and finishing practices are believed to densify and reduce moisture evaporation and maintain sufficient moisture to avoid these conditions. For example, surface hardeners reduce slab surface drying rates. To deter-mine appropriate methods of curing, each decorative mate-rial and method, or combination of materials and methods, should be considered for their ability to prevent moisture loss and should interact with the concrete matrix. Manufacturers of materials such as color pigments and integral and surface hardeners should be contacted for their recommended methods of curing and compatibility of cure methods.

Figure 3.8 (ACI 305R) can be used to estimate water evaporation rates on concrete surfaces early in the bleeding process and determine when supplementary curing methods might be required to reduce rapid drying. This chart provides a graphic method of estimating the loss of surface moisture for various weather conditions. To use this chart, follow the four steps listed in Fig. 3.8. If the rate of evaporation approaches 0.2 lb/ft2/h (1 kg/m2/h), precautions against plastic-shrinkage cracking are necessary (Lerch 1957). Wind speed is the average horizontal air speed in mph (km/h) and should be measured at a level approximately 20 in. (510 mm) higher than the evaporating surface. Air temperature and relative humidity should be measured at a level approxi-mately 4 to 6 ft (1.2 to 1.8 m) higher than the evaporating surface on its windward side shielded from the sun’s rays (Lerch 1957). ACI 305R provides detailed equations and discussion for determining evaporation rates and evapora-tion control measures. Evaporation retarder applied to the surface of concrete reduces the evaporation rate of bleed water by forming a monomolecular film over the bleed water

layer. They should not be used as finishing aids. Consult with the manufacturer for application details and discuss their application during preconstruction or preplacement conferences to establish proper usage.

Do not place plastic film in direct contact with the concrete surface, as it will leave a darkened mottled pattern that appears as stripes or blotches on the surface where it comes in contact with the concrete. The pattern left by this method will be accentuated by color pigments or stains applied to the surface. Specially designed plastic-backed wet curing blankets will aid in proper curing without leaving differ-ential curing marks on the surface when properly installed. Concrete textured in a plastic state should not be cured using the aforementioned wet curing blankets, as the texture will be altered by the blanket contact.

3.9—SealersSealers are surface coatings used for many reasons on

decorative finishes, most important of which is to protect the surface from wear and from contaminants infiltrating the pores of the concrete surface. A sealer’s resistance to dete-rioration or damage from UV exposure is important for exte-rior applications and interior areas exposed to sunlight or high-UV-emitting interior lighting. Some sealer application methods produce unwanted texture to the finished installa-tion. They vary in sheen or gloss intensity, including matte, semi-gloss, and high-gloss. Care should be exercised when selecting coatings for sheen level, clarity, and durability. Slabs should be tested for moisture vapor transmission rate and relative humidity after the initial curing period so that moisture is not trapped below the coating. Sealers should breathe (allow vapor transmission) sufficiently to allow moisture from within the slab to escape.

3.9.1 Penetrating sealers—Concrete tends to readily absorb water because of its pore and capillary structure. Penetrating sealers are typically silane and siloxane-based materials that react with alkaline materials in the concrete surface or moisture to form a water-repellent resin within pores of the concrete matrix and surface. The use of pene-trating sealers may preclude further modification of the concrete. Examples include application of additional color, membrane-forming protective coatings, densifiers, or hardeners.

Penetrating sealers help prevent damage due to mois-ture and chloride ingress by reducing concrete absorbency. Silane water repellents penetrate into the substrate and react chemically with Ca(OH)2 to form a hydrophobic water- and chloride-repellent resin within the pores and on the surface. Unlike silanes, siloxanes are not dependent on substrate pH to react. Siloxanes can react with atmospheric moisture and moisture in the substrate to form the hydrophobic resin. Because of this, siloxanes are ideal for treating noncementi-tious building materials such as brick, stucco, and natural stone.

Because silanes are made up of smaller molecules than siloxanes, they typically penetrate deeper than siloxanes and, thus, perform better on dense surfaces such as cast-in-place and precast concrete. A consequence of this small







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molecular size, however, is that silanes are volatile. The solids content of a silane water repellent, therefore, should be high enough to compensate for the evaporation of reac-tive material during application and curing.

Because penetrating silane and siloxane sealers impart water repellency to concrete, subsequent application of sealers, chemical stains, and dyes—particularly waterborne formulations—will likely not be possible. Some penetrating

sealers darken the concrete surface and require careful reading of product literature and recommended testing.

3.9.2 Membrane forming coatings—Coatings should be selected based on the anticipated in-service wear and protec-tion requirements of surfaces subjected to natural staining and spills. A low-solids coating will generally have some vapor permeability, allowing some moisture to pass out of the slab without delamination. Coatings are available in a variety of options from high gloss (wet look) to flat finish.

Fig. 3.8—This National Ready Mixed Concrete Association (NRMCA)-Portland Cement Association (PCA) nomograph for estimating evaporation rates depicts the effect of concrete and air temperatures, relative humidity, and wind speed on the rate of evapora-tion of surface moisture from concrete (ACI 305R).







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Depending on the end user’s preference or the designer/engineer’s intent, the clarity of the coating is important. Some coatings have a noticeable tint affecting the final color appearance. Coatings generally intensify the color enhance-ment used with concrete. The color appearance may appear to fade as the surface wears or naturally dissipates under UV degeneration. Coatings should be reapplied at regular inter-vals according to an approved maintenance program.

3.10—SafetyDust is a common hazard in the concrete industry. Some

of the coloring chemicals are caustic and proper precau-tions should be followed. Establish health and safety prac-tices appropriate to the specific circumstances involved with the use of each product. Determine the applicability of all regulatory limitations and comply with all applicable laws and regulations, including the U.S. Occupational Safety and Health Administration (OSHA) health and project-specific or local safety standards.

3.11—ReinforcementStructural reinforcing should be considered for substrates

that historically move or settle to avoid unsightly settlement cracking and misalignment of surface planes along cracks or joints. Subgrade preparation per ACI 302.1R will provide adequate support for decorative slabs-on-ground. Local building codes often address required thicknesses of pave-ments for their intended use and some specify reinforcement materials or none at all. Refer to ACI 318 and local building code requirements.

3.12—SustainabilityDecorative concrete delivers all the sustainability benefits

of normal concrete with the added benefit of not having to be coated or covered with another material to achieve an archi-tectural finish. Material optimization is a sustainable benefit of using decorative concrete. It delivers aesthetic benefits, so the use of products such as less-durable floor or wall coverings can be eliminated or decreased. Careful attention to documentation associated with surface treatments and coatings used in conjunction with decorative operations will ensure compliance with volatile organic compound (VOC) regulations and green-building indoor air quality goals.

Many pigments and coloring agents have some recycled content that can contribute to an owner’s green building targets. Supplementary cementitious materials (SCMs), including slag cement and fly ash, are made from recycled products. When their use is appropriate, they reduce the port-land cement clinker content in the mixture paste required to reach the design strength of the concrete, which in turn reduces the embodied energy and greenhouse gas emis-sions associated with a given mixture, while also diverting the SCM product from landfills. The use of SCMs should be carefully evaluated and coordinated with the decorative concrete installer and concrete material supplier, as many products will change the color of the finished surface and or inhibit desired reactions with decorative treatments. In many cases, it is more sustainable to achieve a desired aesthetic

using no SCMs rather than applying more material and labor resources to concrete that contains these products, but has to be covered or retreated.

Decorative concrete typically requires less maintenance than other building systems. Brightly colored decora-tive concrete is more reflective than dark surfaces. Highly reflective concrete requires less illumination and can be used to reduce the amount of artificial lighting required to meet illumination goals. Reflective decorative concrete can contribute to the reduction of Urban Heat Island Effect, which results from dark materials absorbing heat and can contribute to other green building goals, such as providing durable low-maintenance products.

Existing concrete that is improved, reused, or remodeled is a true example of sustainability. It takes far fewer resources to reuse an existing concrete surface than to construct a new one. Concrete can be reused and repurposed more than once before the end of its service life.

CHAPTER 4—PLASTIC CONCRETE COLOR TECHNIQUES

4.1—GeneralThe color of concrete is initially determined by ingredients

in the mixture. Concrete color depends on the color of the:(a) Cement(b) Other cementitious materials, such as fly ash or blast-

furnace slag(c) Aggregates, especially the fine aggregate(d) Water-cementitious materials ratio (w/cm)(e) Coloring agents, including surface treatmentsColor selection charts offered by manufacturers are for

general consideration of hues only and do not indicate what a final color will be. Pigments are subject to regional varia-tions, so proper color specification and preconstruction sample approval is crucial.

4.2—Integral colorDecorative concrete using coloring agents added to the

concrete during the mixing process to achieve a desired color is called integrally colored (Fig. 4.2). The coloring agents can be added to cement or concrete mixtures as fine powder or in liquid form. Integral color is incorporated into the mixture by the concrete producer or added on site. Consistency is paramount regarding the addition of color to the mixture, the quantity of color added, and the time allowed for it to mix completely with the concrete. Use coloring products in accordance with the manufacturer’s recommendations.

Except for coloring agents, the color of the cement has the greatest effect on the concrete color. Integral coloring agents combine within the cement paste to coat the aggre-gate. The effectiveness of integral coloring agents depends greatly on how dark the cementitious materials are in the mixture. In many cases, integral coloring agents have the effect of hiding the color of the cement. Consequently, some colors are easier and much less expensive to achieve than others. For example, earth tones are easier and less costly to achieve than pastels or light colors. White cement is a







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good choice when developing colored concrete in applica-tions where the need for color consistency is high, where the color is more difficult to achieve, or to reduce the amount of pigment added to the mixture. Some lighter hues require the use of white portland cement and cannot be achieved by using gray portland cement.

Traditionally, when integral color was used, the cement was tinted. Colored cements are available in some markets in standard colors and custom blends. Integral coloring is gener-ally muted and less vibrant than other coloring techniques. In some cases, the desired color will not be achieved with integral color, and a different coloring method is required to supplement or modify the integral color after placement. The amount of coloring agent added to the mixture should be limited to not more than 10 percent by weight in relation to the amount of cementitious materials in the mixture.

4.2.1 Advantages—Integrally colored concrete is batched and placed like uncolored concrete (Fig. 4.2.1a and 4.2.1b). With the few exceptions noted herein, standard concreting practices for batching, transporting, placing, and finishing are used (Fig. 4.2.1c).

No special surface finishing techniques are required; however, the surface texture imparted to integrally colored concrete can dramatically change the apparent color due to

light refraction. Projects are sometimes designed to have color changes depending on the time of day and how sunlight or artificial light plays on the textured surface. Any surface finish that is applied to uncolored concrete can be applied to integrally colored concrete.

Integral color is permanent and extends the full depth of the slab. Chips or spalls should not reveal a different underlying color, and exposed interior color will eventually oxidize to the same hue as the surrounding color.

4.2.2 Disadvantages—Integral color can only be used for newly placed concrete. Depending on the color of the cementitious materials and the color admixtures produced, they tend to be in the softer, earth-tone range. Very light or intense colors are difficult to obtain using integral color in common gray cement mixtures. Integrally colored mixtures also cost more than uncolored concrete.

For thicker paving, surface color treatments could be a more affordable option. Compare costs for pavements over 4 in. (100 mm) thick against a similar color achieved with a color hardened surface. Another alternative is to use a

Fig. 4.2—Pigments added to concrete mixtures as dry powders or as liquid solutions offer a wide range of color options (courtesy of Davis Colors).

Fig 4.2.1a—Integrally colored concrete is batched and placed like uncolored concrete (courtesy of Davis Colors).

Fig 4.2.1b—Integrally colored concrete is batched and placed like uncolored concrete (courtesy of Davis Colors).

Fig 4.2.1c–Integrally colored concrete is placed using stan-dard practices (courtesy of Davis Colors).






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topping slab or two-course slabs. The thinner top slab would be colored full depth rather than the overall slab depth.

Research local concrete plants for their color agent capa-bilities; one may have limited facilities for handling special cement or coloring agents while another may have liquid injection systems.

Patching integral color is a trial-and-error effort and often takes several trial batches to achieve a similar color to the surrounding area.

4.2.3 Special procedures and tools—Customary concreting tools such as vibrators, screeds, floats, and trowels are required in the first stages of decorative concrete finishing. Combination or plastic blades should be used on finishing machines to avoid burning concrete surfaces. This precaution is typically unnecessary for concrete that will be polished, ground, or both. Special tools can be used inde-pendently to emboss texture or in conjunction with other patterning tools (Chapter 5). Where different colors are to be placed adjacent to each other, construction joints should be coordinated for efficient placement (Fig. 4.2.3).

4.2.4 Products—Integral color is available in powdered or liquid form. The coloring agent dosage rate is typically expressed in pounds per cubic yard (kilograms per cubic meter), in number of prepackaged bags per cubic yard (meter), or in ounces per hundredweight (mL per 100 kg) of cement. The dosage rate should be determined in advance

of mixing and pigment quantities premeasured based on approved samples or previously installed work using the same mixture design. Because the color should be introduced at the time of mixing, detailed preplacement coordination with the concrete producer, the contractor, and the speci-fying agent in agreement with the owner is crucial. Integral coloring agents can be used in conjunction with texturing processes such as stamping, stencil patterns, traditional tooling, post-placement texturing, grinding or polishing, and other coloring agents such as shake-on color hardeners, colored release agents, pure pigment, and chemical stains or dyes.

Representative job-site samples made in conditions similar to production are a highly recommended practice to assure a positive final result and attainment of expectations.

4.3—Color shake-on hardenersColor hardeners are introduced to the plastic concrete

surface as soon as bleed water begins to escape from the concrete matrix at the surface. Care to evenly distribute color is essential to color uniformity. Hand broadcasting and mechanical spreaders are usually used for this purpose.

As with integral color, color hardeners can be used in conjunction with texturing processes such as stamping, stencil patterns, traditional tooling, texturing mats and rollers, post-placement and texturing (Fig. 4.3a and 4.3b). They can also be used with other coloring agents such as integral color, colored release agents, pure pigments, and reactive stains. Because they are applied at the surface, they do not penetrate deeply into the matrix (Fig. 4.3c).

Dry-shake or broadcast color hardeners are a mixture of coloring agents or pigment, cement, and fine natural aggre-gate or metallic particles that are worked into the top layer of plastic concrete flatwork, becoming a monolithic part of the surface. Although fine aggregates can be mineral or metallic, those most commonly used in architectural concrete are silica sand; fine quartz aggregate; or, for increased slip resis-tance, angular aggregates such as emery and trap rock. Color hardeners should produce uniform, streak-free color and conform to ASTM C979/C979M for color stability.

Fig 4.2.3—Integrally colored concrete places with alter-nating sections deliniated by construction joints (courtesy of L. M. Scofield Company).

Fig. 4.3a—Color hardeners are often used in combination with texturing techniques such as stamping (courtesy of Patterned Concrete of Pennsylvania Inc.).







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4.3.1 Advantages—Hardener colors are generally more vibrant than integral colors and depend less on the concrete mixture components. Repairing spalls and scars is less challenging than a trial-and-error process with integral color. Careful attention to detail allows applicators to place multiple colors with the same truckload of concrete. Color hardeners create a dense, hardened surface that is normally more resistant to wear than the concrete beneath it. Widely used manufacturer’s color charts help establish expecta-tions, but will not exactly match the finished concrete. Using a generic coloring chart to establish a color range allows a wider range of choices among different manufacturers. Color and texture selection should be closely coordinated with the contractor during the sample production process. Samples and adjustments to color selections are easier and less costly than integral color samples.

Surface colored and hardened concrete can be polished successfully if appropriate Flatness F-Numbers (FF) are specified and achieved.

4.3.2 Disadvantages—The large number of color choices can lead to difficulty in color selection. Only the top 1/8 to 3/16 in. (3 to 5 mm) of the concrete surface is colored. Exposed edges may need to be colored after concrete is rigid enough to remove formwork and still plastic enough to accept working the color into the surface. Saw-cut joints will reveal the uncolored concrete below the colored surface and require additional treatment, grout filler, or joint sealant or filler. Grinding and polishing operations performed on a colored surface removes a portion of the concrete surface. This will expose the base color if the concrete surface color is not built up sufficiently or if grinding beyond Class A is necessary (7.2.5).

4.3.3 Special procedures and tools—No special tools or equipment are needed for installing shake-on color-hard-ened concrete. Special tools are used to emboss texture in conjunction with color hardeners, including patterning tools such as stamps, texture mats and rollers, and stencil pattern techniques. Broadcast and work color hardener into the surface using only wooden finishing tools while the surface

is damp to preclude a too-rapid closing of the surface. Refer to ACI 302.1R for guidance.

4.4—Exposed aggregateExposed aggregate can be produced by one of two single-

course methods:(a) Exposing decorative aggregate from within the

concrete matrix(b) Seeding decorative aggregate into the surface of a

normal concrete design mixtureExposed aggregate can also be produced through tech-

niques that require two courses:(a) Using an aggregate topping mixture over a normal

concrete base course(b) Applying a polymer mortar decorative aggregate

topping4.4.1 Exposed decorative aggregate from within concrete

matrix—Exposing aggregate within the concrete can be accomplished by using the following methods: surface retarders (Fig. 4.4.1), sandblasting, acid etching, grinding, or water-washing (with pressure or without) the cement matrix away from the aggregate before final set.

4.4.2 Seeded exposed aggregate—Aggregates can be broadcast into fresh concrete or topping mortars and embedded into the mixture with vibration or floating. Expo-sure is accomplished by either a surface retarder or washing to expose the aggregate before final set. Recycled crushed, graded, and acid-etched glass produced for this purpose may be used as exposed aggregate. Seeded aggregate into the surface typically yields a more uniform appearance than can be attained by depending solely on the aggregate in the matrix of the mixture. A jitterbug tool is helpful to consoli-date the added aggregate into the surface, bringing additional cement paste to the surface to coat the added aggregate to lock it into the concrete matrix.

Distribution of the seed aggregate can be accomplished either by broadcasting equipment or by manual distribution with shovels. Prewash the aggregate to assure removal of

Fig. 4.3b—Color hardeners are often used in combination with texturing techniques such as stamping (courtesy of Patterned Concrete of Pennsylvania Inc.).

Fig. 4.3c—Delamination of color shake-on hardener illus-trating depth of coloration (courtesy of Patterned Concrete of Pennsylvania Inc.).







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detrimental contaminants. Dampen before broadcasting over the slab surface, after bull floating, and near the end of bleed water evaporation. It is important that no one walks through the fresh concrete, but rather broadcasts the seed aggregate to avoid foot tracks in the final finish. The seeded aggre-gates can then be worked into the surface; accepted practice calls for using a fresno trowel or functionally similar tool at multiple angles until the aggregates are cleanly seated in the surface. No additional finishing is required if the surface is to be ground and polished.

4.4.3 Two-course decorative aggregate topping—This mixture design is used for topping courses typically containing different aggregates from the base course to impart a decorative appearance. Using a two-course topping may result in lower costs than monolithic applications; the topping mixture required for decorative aggregate could be more costly than for a base course mixture. Two-course applications can produce results similar to seeded or broad-cast applications. Care should be taken to keep the base course plastic to allow for a proper knitting of the topping and base courses.

It is beneficial to use a polymer bonding agent or cement paste if the bond between the two courses is likely to be affected by the base course becoming too dry or setting up. Placement delays in excess of 2 to 3 hours, depending on weather variables, may require the use of polymer bonding agents recommended for the in-service use of slabs. This method is often used in areas subjected to freezing-and-thawing conditions. Refer to guidance for topping slabs in ACI 301 and 302.1R.

4.4.4 Polymer mortar aggregate toppings—Embedded aggregates in polymers can also be used as a decorative application. Consult with the polymer grout manufacturers for their specific directions for use.

4.4.5 Surface retarders—Surface retarders are usually formulated from saccharides that are sprayed or brushed onto the trowel-finished concrete surface. This can be done over normal concrete or special aggregate. Usually the partially

hardened and retarded concrete is washed off within 24 hours to expose the aggregate. Controlling coverage of these materials is difficult and requires experienced craftsmanship.

Exposing mixture aggregate by weakening the surface of the slab has the inherent risk of weakening the cement bond of the aggregate while it is being exposed. Subsequent grinding and polishing operations can lead to aggregate release or popouts.

4.4.6 Sandblasting—Sandblast techniques have been used for years to expose aggregates and produce other effects. Sandblasting can be an environmental problem as it gener-ally results in microsilica particles being disbursed into the air and requires experienced, skilled labor to produce the desired effects. Abrasive blasting should be delayed until there is little chance of damaging the concrete with the hose or any other equipment the operator brings onto the slab. Refer to Chapter 7 for information on special sandblasting techniques.

4.4.7 Acid etching—The application of acid-etching prod-ucts requires diligence to protect the environment around the work area. Residue may require special handling, contain-ment, removal, special disposal, or a combination of actions. The amount of acid required is a function of the age and hardness of the concrete to be etched (Fig. 4.4.7). The use of acids requires special protection of the workers. Apply an alkaline solution to the concrete surface following the acid application. Some applications will require a water rinse. A pH test should be performed to ensure that the pH level requirements for subsequent treatments are met.

4.4.8 Pressure-washing—Pressure-washing is a common method of exposing aggregate, as machines are available with many configurations of delivery pressure. The amount of pressure required varies based on the maturity of the concrete surface paste, effectiveness of a surface retarder, and weather conditions. Experienced, skilled workers with the ability to properly determine the distance from the area to be washed and the shape that the nozzle projects onto the concrete are paramount to consistent removal and final appearance. The resultant slurry and waste water should be confined and disposed of as dictated by local environmental constraints to prevent contamination of water sources or

Fig. 4.4.7—Acid etching concrete can be done at various levels of concrete age (courtesy of L. M. Scofield Company).

Fig. 4.4.1—Examples of exposed aggregate achieved on identical slabs with surface retarders rated for different exposure levels (courtesy of Nick Sorrentino).






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runoff areas. Exercise caution and patience during this process; once the cement paste is removed, it cannot be replaced, resulting in costly delays and reinstallations. The depth of surface removal desired should be agreed upon by the end user and designer using preconstruction samples produced by the contractor of choice.

4.5—AdvantagesMaterials and aggregates may be obtained locally, which

is considered a green building practice by the Leadership in Energy and Environmental Design (LEED) rating system. Recycled glass is also a sustainable resource. Natural mate-rials are durable and provide a serviceable, safe surface for traction in wet or icy weather and are attractive and flexible for architectural intent, planning, and scheduling. The size and color variations of aggregate are numerous. In conjunc-tion with integrally colored concrete or acid stains used to augment the surrounding exposed cement paste color, exposed aggregate paving provides a multitude of designer choices. Exposed aggregate can be used with patching and overlay mortars as a post-placement topping. In many locations, the aggregates are harder and more durable than cement and other concrete finishes.

4.6—DisadvantagesSpecifying aggregate that must be shipped from remote

locations can dramatically increase the cost of installation. Exposed aggregate paving can be difficult to replicate or patch to match the existing aggregate. Paving left unmain-tained can deteriorate more rapidly in some colder climates due to moisture infiltration around surface-adhered stones, which can cause popouts. Overexposure or bad gradation of stone can result in loss of surface aggregate.

4.7—Special procedures and toolsBrooms with water-spraying attachments are used to wash

off cement paste to expose the aggregate. Power washers with 3500 psi (24 MPa) or greater water pressure are helpful for aggregate exposure in the hands of an experienced oper-ator. Mechanized rotating brush equipment is used on larger projects to remove paste. Larger seeded aggregate projects typically require automated spreader equipment to ensure aggregate spreads uniformly. Depending on the seeding method, large projects require work bridges for access to the slab surface.

4.8—Required productsThe following products can be used when working with

exposed aggregate:(a) Specialty or topping concrete mixtures custom

designed to include special aggregate with select sizes, shapes, and colors or designed to accept loose aggregate to be seeded on the surface

(b) Prewashed aggregate, recycled glass, or both, which are appropriately cleaned to ensure positive adhesion to the cement paste for seeded applications

(c) Surface retarder or acid-based solutions to keep the cement paste soft at the surface until it can be washed off for exposure of aggregate

(d) Acid neutralizing solution if acid-etching process is used

(e) An appropriate sealer suited for the in-service conditions

4.9—SafetyIf acid etching or sandblasting options are used, the indi-

viduals should use a respirator or OSHA-approved face mask respirator to avoid inhaling and facial contact with the acid fumes and microsilica fines.

4.10—MaintenanceWashing, bleaching, and degreasing are often required of

most concrete. Bleaching removes many types of stains from organic materials, and degreasers remove a wide variety of oils, gasoline, and solvents. The appropriate application of these products requires on-site testing and product knowl-edge. A sealer should be reapplied periodically based on in-service use and the manufacturer’s recommendations.

CHAPTER 5—PLASTIC CONCRETE TEXTURING AND PATTERNING TECHNIQUES

5.1—Texturing: embossing, imprinting, stenciling, and stamping

5.1.1 General—Concrete can be embossed or stamped to resemble materials such as brick, slate, stone, or wood plank and feature a custom graphic pattern or special shapes such as horseshoes or other removable objects. Texturing by use of stamps, texture skins, stencil, texture rollers, natural objects, score joints, or a combination of patterning tech-niques can be used to create unique installations limited only by the designer/engineer’s imagination and the contractor’s experience and abilities (Fig. 5.1.1a and 5.1.1b).

Decorative concrete is subject to cracking and scaling if proper construction and maintenance procedures are not followed. Many textured, stamped, and stenciled concrete projects make use of fiber reinforcement. As noted in ACI 544.5R, fiber reinforcement helps reduce plastic shrinkage cracking and should be considered for use when appropriate. Properly designed concrete mixtures and planned construc-tion joints will mitigate most unwanted drying shrinkage cracks. Feature strips incorporated into a design can help avoid mismatched patterns and break up pattern fields into easily managed areas. Contractors and their field managers responsible for performing decorative concrete should have adequate knowledge of and experience working with concrete and implementing good workmanship practices.

5.1.2 Preparation—All preparation, including the subgrade, reinforcement, formwork, and expansion/contrac-tion joint layout, should follow ACI 302.1R. Precautions may be needed to protect surrounding surfaces so that fresh concrete from any new placement does not reach and damage previously finished sections.







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5.1.3 Initial finishing—Surfaces of placed concrete should be struck off (screeded and bull floated) to the proper grades and pitch to encourage proper water drainage flow off the slab or to drains. Wood floats or tools will be required for some applications. Protect the surface from rapid moisture loss.

5.1.4 Timing—Special effects, including proper applica-tion of color hardeners, embedded items, and imprinting of the plastic surface, should be completed by an experienced, organized crew to ensure a uniform surface. The window of time available for these processes will vary based on ambient conditions and mixture constituents, usually within the first hour after placement. The size of concrete place-ments should be based on what the contractor can accom-plish while producing a uniform finished surface.

5.1.5 Joints—The expansion and contraction joint pattern, if applicable, should be laid out to fall within pattern joints or at feature strips (Fig. 5.1.5a and 5.1.5b). Preplan and establish layout lines for patterning before placement begins. Contraction joints can be cut into the surface either with deep groovers with a minimum depth of d/4 while the concrete is still plastic. Alternatively, contraction joints can be saw-cut to a minimum depth of cut of d/4 into the slab when the surface is solid enough to resist spalling in all cases within 24 hours of initial concrete set.

5.1.6 Curing—Care should be taken in curing embossed concrete so that the curing method does not inhibit secondary treatments. The curing method should commence when the surface cannot be damaged by curing action. Surfaces that are to be sealed with a penetrating sealer should not be cured with a membrane-forming curing compound. Concrete curing cannot be completed until powder release agents are sufficiently removed and the post-placement detailing process is complete. Leaving form material, powder release agents, or both, in place may be acceptable for initial cure. Dry releases are normally removed after 3 to 5 days with power washing equipment and then sealed. Clean and seal other types of applications after an initial cure time of

approximately 7 days. The required drying time is deter-mined by the sealer manufacturer’s specifications.

5.1.7 Sealants (joint treatments)—Seal all contraction and expansion joints using a sealant of similar or contrasting color per the designer/engineer’s choice. Installation of the

Fig. 5.1.1b—Textured stamps for creation of stamped concrete (courtesy of Butterfield Color, Inc.).

Fig. 5.1.5a—Careful planning of joint placement ensures seamless incorporation with post-placement texturing and patterning techniques (courtesy of Patterned Concrete of Pennsylvania Inc.).

Fig. 5.1.1a—Textured stamps used during initial placement are available in a wide range of patterns (courtesy of Butter-field Color, Inc.).







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sealant should be delayed for 28 or more days. The pattern joints can be grouted with a mixture of sand, cement, water, and coloring agent, if desired. Care should be exercised to avoid staining stamped or imprinted concrete surfaces with grout products.

5.1.8 Detailing (plastic stage)—Before sealing decorative finishes, perform detailing while the concrete is in its plastic stage to ensure distribution of surface color applications, satisfactory texture imprint, and jointing. Detailing includes, but is not limited to, patching and repairing any surface splits and deepening or widening any imprinted lines that are too shallow to give the joint uniformity. Detailing is a common practice that is required on most decorative installations.

5.1.9 Detailing (hardened stage)—Detailing of hardened, imprinted, or stamped concrete requires multiple steps that might include:

(a) Scrubbing and washing until all excess release agent has been removed

(b) Minor patching of surface using matching colored cementitious material

(c) Chiseling or grinding of joints to remove concrete paste created by imprinting tools

(d) Minor patching or filling of surface splits(e) Touching-up chiseled joints using the same color as the

release agent used(f) Preparing the surface to accept a sealer, if requiredPost-placement colors can be used for additional high-

lights or antiquing if a final protective coating is being used. The sealer should be maintained because most added antiquing color is surface-applied and not self-sustaining or embedded in the slab surface.

5.2—Stamping5.2.1 General—Imprinting concrete by pressing a form

into the surface of plastic concrete generally uses the term “stamped” to describe decorative embossed concrete. Stamping is achieved by using integrally colored concrete, colored shake-on hardeners, or both. A liquid or powder surface release agent, either with or without color, is required to ensure that intricate texture and patterns are not

removed from the concrete surface as stamps are peeled back or moved to their next location. Texture and patterns are imparted to the concrete surface by compaction, forcing the imprint into the surface (Fig. 5.2.1). Proper care should be taken to ensure that the tools line up with surrounding surface and layout points as well as the previous embossed lines already created. The stamping process should begin when the prepared concrete surface is able to resist hand-prints or footprints from being transmitted through the imprinting tools.

5.2.2 Special procedures and tools—Imprinting concrete requires unique tools such as stamps, cookie-cutter-type tools, textured mats, texture rollers, hand tools, small-detail finish patterns for use near walls or obstructions, compaction devices, wood or plastic floats, special edging tools, special jointing tools, and early-entry concrete saws for cutting contraction joints.

5.2.3 Required products—In addition to a concrete mixture design suitable for imprinting concrete, the following prod-ucts are used alone or in combination to enhance the appear-ance of stamped finishes:

(a) Coloring agents (dry-shake hardeners or integral colors)

(b) Colored release agents(c) Liquid release agents, colored or clear(d) Reactive stains or concrete dyes(e) Joint sealants5.2.4 Advantages—Embossed colored concrete installa-

tions are unique, attractive, and artistic. Permanent color, pattern, and texture effects not obtainable with any other concrete process are produced by means of stamps. Imprinted concrete provides a cost-effective, decorative finish in an unlimited array of patterns and colors. With proper crafts-manship, it can leave a durable and aesthetically pleasing surface for many years. Unlimited combinations of colors, textures, shapes, sizes, and procedures can be combined during imprinting or as a post-placement to create a unique appearance (Fig. 5.2.4).

5.2.5 Disadvantages—Imprinted concrete is a custom product manufactured in the field; slight variations in color, texture, and depth of imprint are expected. Variances should be discussed in a preconstruction meeting by the owner, specifier, and contractor. The owner should realize that some of these variations will be detailed in the cleaning and sealing process as noted in 5.1.8 and or 5.1.9. This is a normal procedure and should be expected. A spalled surface will expose aggregate and uncolored concrete when dry-shake hardeners are used, making repair difficult. A lack of texture or flat spots can result in a slippery surface when wet if topical sealer is applied. Following the radius or curved areas is sometimes difficult. For example, pie-shaped pieces, such as bricks, cannot be cut to follow radius curves. Texture will be lost if proper materials are not used in heavy vehic-ular/pedestrian traffic areas.

5.3—Texture and pattern rollersEmbossing concrete by texture rollers can be used in

conjunction with patterning tools such as stencils, or used

Fig. 5.1.5b—Careful planning of joint placement is impor-tant for post-placement texturing and patterning techniques (courtesy of Patterned Concrete of Pennsylvania Inc.).







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alone to create patterns by cutting score joints into the concrete. Texture rollers are horizontal cylinders covered with a pattern or texture relief around their circumference (Fig. 5.3). They come in various sizes, from small hand-held rollers used on borders and in hard-to-reach locations, to large-scale rollers that are 6 to 9 in. (150 to 230 mm) or more in diameter and 24 or 36 in. (610 to 910 mm) wide weighing 50 lb (23 kg) or more. As large a roller as practical should be used initially with a smaller roller of the same texture or pattern for the edges and details around vertical penetrations.

5.3.1 Required products—Integral pigments, dyes, or dry-shake color hardeners are introduced integrally or by broad-casting into the plastic surface. Liquid or powdered release agents are applied prior to receiving a texture. Specially formulated release agents, either liquid or dry, are used to prevent fresh concrete surfaces from sticking to the roller surface. Alternatively, thin layers of plastic sheeting are sometimes used as a temporary barrier between the concrete and textured roller. Post-placement coloring agents can be applied to hardened surfaces.

Fig. 5.2.1—Stamps are often made of flexible materials and are available in various patterns. (Note: (a), (d), (e), and (f) cour-tesy of Butterfield Color, Inc.; and (b) and (c) courtesy of Marshalltown Company.)






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5.3.2 Special procedures and tools—Use rollers designed only for concrete finishing. Many rollers are internally weighted to make the process of impressing the metal, plastic, or polyurethane texture/pattern wrapped around them into the concrete surface. Larger-width rollers (24 to 36 in. [600 to 900 mm]) are used for main area production whereas smaller rollers (6 to 12 in. [150 to 300 mm]) are recommended for details and tight spaces. Small matching texture mats can also be used.

5.3.3 Advantages—Because rollers can be used to contin-uously imprint patterns, production is not limited by the number of stamping mats available in a particular style. Contrasting color can be added to the score joints with excess dry-shake color or colored paver grout swept into the joints after the final sealer is dry. Many rollers allow the addition of water to the roller drum to adjust the roller weight to compensate for different degrees of concrete hard-ness. Rolling can start as soon as the concrete surface will allow the roller to travel along the surface without picking up the cement paste. As with other patterned finishes, surfaces tooled using textured rollers can be stained after the concrete is cured to simulate natural materials using multiple colors or secondary stain treatments.

5.3.4 Disadvantages—Patterned roller drum materials, such as aluminum, can react with the concrete and interfere with chemical treatments. Alignment with previous applica-tions can be difficult to maintaining the pattern alignment with the previous imprint run. If polyethylene film is used as a release or protective film between the plastic concrete and the tool, it can produce a high-gloss concrete surface.

Roller imprinting is limited by the length of float handle extensions that can be added and still accurately and effi-ciently emboss the plastic concrete surface. Pattern rollers

are limited by the circumference of the roller to producing a repeating design typically of brick or stone impressions. These patterns may be difficult to impart on irregularly shaped work areas or areas where aligning the roller with the previous pass is impractical.

5.4—Stencils (paper templates)Stencil patterns can be used effectively to produce a

variety of standard and custom patterns. This process creates a shallow joint that appears to be mortar between the patterns. The apparent joint is actually the colored or uncol-ored concrete matrix beneath. Generally, stenciled concrete is installed using shake-on color hardener alone or with

Fig. 5.2.4—Finish achieved with dissimilar stamped stone and border patterns combined with different color treat-ments (courtesy of Butterfield Color, Inc.).

Fig. 5.3—Textured rollers are available in various sizes and yield continuous patterns in freshly placed concrete (cour-tesy of Marshalltown Company).







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integral color added to the base concrete mixture to create a colored contrasting mortar joint appearance. Stencils inhibit color hardener applied to the surface of concrete where the stencil pattern is slightly embedded with the concrete. Sten-ciled surfaces simulate natural materials set in grout, such as random stone pavers, brick, slate, cobblestone, and custom logos or shapes. Different texturing techniques applied in conjunction with stencils can create depth and simulate natural textures. Texture rollers and mats are often used for this purpose. Broom or sponge finishes over brick patterns are often used to replicate brick textures.

5.4.1 Special procedures and tools—Special heavyweight paper or patterns are the typical tools for stenciling. Custom stencils can be made from many materials, such as foam core board, masonite, and acrylonitrile butadiene styrene (ABS) plastic. Tools can include texture rollers, sponges, brooms, and texture mats. Shake-on or broadcast color hardener is required for stencil concrete. Integral color and post-place-ment staining are optional. Sealers should be used to protect the concrete finish.

5.4.2 Advantages—Texturing and embossing are low-profile, making this process well suited for low-drainage surface applications and where Americans with Disabilities Act (ADA) compliance is a concern. Paper templates can be very effective because the final exposed surface is apparent during the coloring and texturing process. Simulated brick or stone can be customized with additional pigments worked into the concrete surface. Matching the previous pattern, establishing a starting point, and alignment are simpler using a heavier pattern material than using reusable templates. Stenciled concrete is generally durable and usually complete the day after placement. Next-day cleanup consists of blowing off flashing waste left from stencil removal. If desired, a penetrating sealer can be applied according to the manufacturer’s recommendations. Detailing, normally asso-ciated with stamped concrete, is normally not as intense and embossing edge cracking not generally encountered. Over-working and retouching the surface is normally unnecessary, producing a very durable finish requiring low maintenance.

5.4.3 Disadvantages—Paper templates are usually single-use and create a great deal of waste. Separated paper recy-cling is recommended. Polyester templates are reusable but have a limited life and are difficult to clean, store, and recycle. Removal can be difficult if the stencil is allowed to fully saturate with water or left in the concrete too long. Limited pattern selections are available; however, custom patterns can be created for special feature areas and logos.

5.4.4 Safety—Crews coloring concrete surfaces with shake-on color hardeners should exercise care in containing the powdered color and protecting adjacent surfaces from airborne color. In the same way, crews using integrally colored concrete should protect adjacent surfaces from unwanted colored footprints and stains from fresh concrete. Workers should also use respirators or other devices as required by OSHA for protection from inhaling pigments and silica dust.

5.5—Object impressingObjects such as leaves, branches, and shells can be used

for impressing a pattern into concrete. Seashells, stones, and glass can be permanently embedded to create a decorative look; these objects should be clean and free of loose mate-rials. Any portions left in the concrete should not deteriorate over the expected service life. Metal objects, such as iron parts, can rust when exposed to water.

5.6—Texturing with standard tooling5.6.1 Broom finish—Brooming is the most common exte-

rior paving texture. Broom finishes function as skid protec-tion in exterior walkways and are normally specified to be installed perpendicular to the direction of the pathway. Rectilinear brooming is common and can be accomplished by less-experienced workers. Decorative broom finishes, such as swirls and sine curves, however, require planning, design, and craftsmanship. Broom finishes can be specified in varying degrees of depth and coarseness. Using color in concrete and changing the direction and coarseness of broom finishes can dramatically change the viewed color due to the change in light refraction. Samples should be viewed and approved from different angles and in different lighting conditions before installation.

5.6.1.1 Fine broom finish—A fine broom finish is normally achieved with a horsehair floor broom, which leaves fine grooves in a concrete surface less than 1/32 in. (0.8 mm) in depth.

5.6.1.2 Medium broom finish—A medium broom finish is normally achieved with a horsehair or synthetic bristle finishing broom and leaves grooves in the concrete surface 1/32 to 3/64 in. (0.8 to 1.2 mm) in depth.

5.6.1.3 Heavy broom finish (rake finish)—A heavy broom or rake finish is normally achieved with a street broom or synthetic bristle finishing broom that leaves deep broom grooves 3/64 to 1/8 in. (1.2 to 3.2 mm) in depth.

5.6.1.4 Sanded or light sandblast finish—Finishes less than 1/64 in. (0.4 mm) deep are generally produced by a smooth trowel, special surface retarders, and sandblasting or water blasting to remove a thin layer of cement paste and create an appearance of a gritty yet smooth surface.

5.6.1.5 Smooth trowel finish—A smooth trowel finish is probably the most commonly specified interior concrete final finish. It is also one of the most technically difficult to achieve without error, especially when done in variable weather conditions using colors. Hard steel troweling or burning causes coloration differentials that may be undesir-able. Smooth trowel finishes alone are not recommended for exterior applications or for surfaces that become wet in service as they become slippery. Secondary applications such as acid etching, sand, or water blasting and saw-cutting grooves improve traction and increase installation costs. Sealers with fine aggregate or ground polyethylene can also be used; however, sealers should be regularly maintained to ensure safety.

5.6.1.6 Rock salt finish—A salt finish traditionally is accomplished by broadcasting rock salt onto a fresh concrete surface. The salt granules are then pressed into the concrete






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using a fresno trowel or functionally similar tool. The salt absorbs water and becomes a liquid, leaving a crystal imprint in the finished concrete surface. Washing off all salt residue after the concrete surface is cured enough to resist damage from water is highly recommended, especially in areas subjected to salt product applications for snow and ice. Rock salt finish has been used for many years in southern climates and can replicate weathered, imported quarry stone, especially when score joints are introduced to create tile shapes. Some stamp, mat patterns, and roller finish manu-facturers offer a rock-salt finish without introducing salt to the concrete surface. Salt scaling and spalling can occur in areas that experience freezing-and-thawing cycles.

5.6.2 Sealing—Many curing compounds are also sealers when a second or third coat is applied. Sealers are used as a final wearing coat and should be inspected periodically for restoration. A coat of cure-and-seal compound does not necessarily provide a final sealer. Penetrating salt protec-tant sealers are not effective if a membrane-forming curing compound is applied, as they cannot penetrate through the membrane. To best protect the concrete from freezing-and-thawing damage, it is important that air-entrained concrete be used for all work that is exposed to these conditions. In addition, sealing the concrete will provide additional protec-tion for the slab. Consult manufacturer’s instructions for all sealers.

5.6.3 Maintenance—To preserve the imprinted concrete and to keep it looking like new, suggested procedures should be performed on a periodic basis. They include power-washing the surface, detailing of any surface defects, and resealing the surface in accordance with the sealer manufac-turer’s recommendations. Frequency of the reseal should be determined by the type of sealer used, the environment the slab is exposed to, and the amount of traffic.

No deicers should be used on unprotected concrete surfaces. This is primarily due to the increased number of freezing-and-thawing cycles created by using a deicer, which lowers the freezing point of the water-deicer mixture.

CHAPTER 6—POST-PLACEMENT COLORING TECHNIQUES

6.1—GeneralDecorative concrete coloring can also be achieved during

post-placement. This chapter describes methods and mate-rials that have been used to enhance previously placed hard-ened concrete.

Post-placement coloring techniques are applied to existing plain concrete, new concrete, or cementitious toppings placed with the intent of applying decorative color after the cementitious material is cured. Exercise caution during the curing period to avoid sealing or closing the concrete surface. Membranes applied to newly installed concrete will inhibit the penetration and proper reaction of the staining agents. Use of non-membrane, non-staining, evaporation retarding curing methods and specially designed curing covers in conjunction with a wet surface with air excluded is encouraged.

Color hardened flatwork, whether reactively stained or colored with dyes (Fig. 6.1a) and then densified, diamond polished, or coated with a gloss coating or commercial floor polish (Fig. 6.1b), has an attractive sheen that makes it ideal for interior floors. If multiple colors are applied, contrac-tion joints or decorative score joints can be used or effec-tive masking applied to polished concrete to prevent the stain from bleeding into adjacent areas (Fig. 6.1c through 6.1g). Score joints should be a maximum 1/16 in. (1.5 mm) in depth if they are intended to remain unfilled.

Although acrylic stains are often confused with concrete reactive stains, they are a type of concrete coating that is similar to paint and, therefore, not discussed in this guide.

6.1.1 Concrete surface preparation—The surface should be open, clean, and dry before application of the reactive stain or concrete dye. Spray a fine mist of water on the surface to ensure an even absorption of staining material. Areas where water beads up will not absorb staining mate-rials properly and could result in unwanted mottling of stain. The type of equipment and cleaning method required to prepare the concrete substrate depends on the surface condition. All dirt and contaminants, adhesives, coat-ings, nonpenetrating sealers, water repellents, and curing compounds should be removed so that the reactive stain

Fig. 6.1a—Ground and polished concrete combined with reactive stains and dyes achieve striking aesthetic effects (courtesy of Epoxy Systems Inc.).

Fig. 6.1b—Reactive stains of various colors are used to achieve intricate patterns that have been sealed and polished to a high gloss (courtesy of Butterfield Color, Inc.).






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or dye can penetrate into the concrete surface. Cleaning is usually performed with pressure washers, self-propelled rotary scrubbing machines, manual scrubbing machines, sanding machines, or stiff-bristled brushes. Cleaning agents may also be required to remove blemishes from construc-tion activities. Trisodium phosphate (TSP) is often used to lift petroleum-based marks, and bleach is used for organic material stains. After blemishes have been treated, another scrubbing pass is recommended.

Concrete that cannot be successfully cleaned by simple methods can be sandblasted, shotblasted, or high-pressure washed. Surface abrasion methods should be applied care-fully to remove as little material as necessary to achieve a clean surface. Grinding should not be used to remove oil

or grease contamination; the heat of grinding will drive the contamination further into the slab, making ultimate removal more difficult.

After cleaning and drying the floor, and prior to the appli-cation of post-placement coloring agents, a moisture trans-mission test should be performed in accordance with ASTM F1869 to confirm that all moisture within the concrete is

Fig. 6.1d—Combined reactive stain and pigment applica-tion with freehand score joints filled with sealant (courtesy of Concrete Artisans, LLC).

Fig. 6.1e—Combined reactive stain and pigment application with colored joint sealant (courtesy of L.M. Scofield).

Fig. 6.1f—Combined reactive stain and pigment application with colored joint sealant (courtesy of L.M. Scofield).

Fig. 6.1c—Polished concrete combined with reactive stains and freehand score joints filled with colored sealant (cour-tesy of Concrete Artisans, LLC).






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below the recommended level of transmission required by the color and final coating manufacturers. Testing for rela-tive humidity is also recommended if the slab is to receive a decorative gloss coating material. Test values should conform to the coating manufacturer’s recommendation. Maximum values are generally less than 5 lb/1000 ft2 (2.5 kg/100 m2) of water vapor per 24 hours of vapor transmission and less than 90 percent relative humidity (ASTM F2170).

6.1.2 Test section—Work should be performed by expe-rienced, well-trained workers who are closely supervised to ensure that design intent and proper processes are followed. Samples and experimentation of combinations should be exercised along with the designer/engineer, owner, and contractor of choice before any work is performed (Fig. 6.1.2). Staining mistakes are costly to repair and, in some instances, impractical to adjust.

Caution should be exercised in selecting a test area; the response of the slab to chemical treatment will vary with its history. For example, in older slabs, a previously protected section of floor will most likely have different reactivity than an unprotected section. Because wide variations in color can occur, a project may require several representative test section areas be selected to determine the materials and construction procedures that will produce the desired color effects for those areas. Special and unique effects are created using materials such as cereal, metal shavings, sawdust, or other mildly reactive or absorbent materials added to the surface while a reactive stain is wet.

Chemical stain colors can be applied by overspraying a previous color with use of a spray bottle or sponge. Any number of effects can be created by individual experimen-

tation with application methods and materials. For consis-tency, notes should be taken during the sample process, including the type and dilution rate, if any, of the stain, the color used, and the amount of reaction or burn time allowed.

6.1.3 Special features—Many projects have special feature designs or patterns that require precise layout and location. This work should be done after the floor is prepared to receive the stain to confirm that pattern dimensions work for the intended locations and any prefabricated appliqués intended for use to facilitate stain separation are properly made. Appliqués should be produced to the lines and shapes directed by the designer and have adhesive backing that will resist the reactive staining agent from bleeding outside of the pattern area. Once the staining process begins, timing is critical. Preplanning of the sequence and making sure the crew understands procedures is of utmost importance (Fig. 6.1.3a through 6.1.3g). Layout marks on the prepared surface should be made with removable marker or white chalk without any penetrating dyes. Unwanted shadows or lines may show up after staining materials are applied without careful removal of layout marks.

Take precautions to avoid stain bleed. Decorative scoring is one method to ensure clear definition of varying colors and patterns (Fig. 6.1.3h). For decorative scoring, recut the scoring after the sealer is applied to clean out any residual sealer from the joint. This ensures a proper grout bond if joints are scheduled to be grout-filled. Sealants, if used

Fig. 6.1g—Combined reactive stain and pigment applica-tion with freehand score joints filled with sealant (courtesy of Concrete Artisans, LLC).

Fig. 6.1.2—Test sections are used to adjust dye combinations and color dilution levels (courtesy of James Vermillion).






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in place of grout, should be compatible with the sealer. Rescoring is not always necessary in nonmoving joints. Backer rod or bond breaker at the moving surface of a joint may be required for active joints receiving sealants.

6.2—Reactive stainsReactive stains are often used on imprinted concrete

where their uneven colors help reproduce the look of natural building materials such as stone or wood or add an antique look to tile or brick patterns (Fig. 6.2a and 6.2b). Complex and intricate designs can be produced when templates or stencils are used and the stain is applied to selected sections of floors or hardscapes.

When used on exposed-aggregate concrete, reactive stains will color the concrete matrix and can color the aggregate, depending on its mineral composition (Fig. 6.2c and 6.2d).

Fig. 6.1.3b—Registration marks align work (courtesy of Floormap Designs).

Fig. 6.1.3c—Having registration marks to align work is crit-ical in placing overlapping pieces of large stencils (courtesy of Floormap Designs).

Fig. 6.1.3d—Stains are applied in successive steps to achieve multiple layers of color (courtesy of Floormap Designs).

Fig. 6.1.3e—Weeding removes stencil layers to expose concrete to a sequence of staining applications (courtesy of Floormap Designs).

Fig. 6.1.3a—Applicators using multilayered designer use registration marks to align work. Preplanning is key (cour-tesy of Floormap Designs).






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For renovation work, chemical stains are often used over cementitious toppings and as a transparent color wash over dry-shake color hardeners for new concrete projects. The surface should be unsealed and free of any curing compounds or membranes, as these barriers inhibit stain penetration.

Reactive staining is a permanent process using solu-tions of one or more metallic salts that penetrate and react with compounds in the concrete to form insoluble colored deposits in the concrete matrix. They usually contain diluted hydrochloric acid, although other acids are also used. Reac-tive stains should not be used on freshly placed concrete. Concrete should be allowed to gain sufficient strength so that the surface is not damaged or excessively etched by the reactive stain. Most manufacturers recommend that the concrete be allowed to cure for 28 days. Many stain manu-facturers can offer knowledgeable suggestions for use of their product based on experience and test applications. The concrete surface should be protected as soon as practical after staining.

The actual color created by the reaction is affected by the chemical content and natural color of the concrete matrix. The color produced from the same container of reactive stain can vary widely from project to project and even across the surface of the same slab because of variation in the concrete mixture delivered from load to load (Fig. 6.2e). This is unique to each slab, with many designers and owners enjoying the knowledge that their project is not reproducible. The Committee knows of no standards or tests governing the quality of acid stains.

6.2.1 Reactive stain preconstruction planning—The area should be divided into manageable work sections. Plan applications so that wet surfaces are not walked on when

Fig. 6.1.3f—Weeding removes stencil layers to expose concrete to a sequence of reactive stain applications (cour-tesy of Floormap Designs).

Fig. 6.1.3g—Stencil placement often requires more than one person (courtesy of Floormap Designs).

Fig. 6.1.3h—Decorative scoring following reactive staining (courtesy of L. M. Scofield, Inc.).

Fig. 6.2a—Reactive stain (courtesy of L. M. Scofield, Inc.).







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chemically staining flatwork or permanent footprints could be left on stained surfaces or the stain tracked to other areas. Spike-soled shoes are recommended while in the stain work area. They should be removed on an impervious surface or

area that will be covered by other flooring materials to avoid unwanted footprints or stains.

While some mistakes can be addressed immediately, others should not, as they will only be made worse by trying to correct them without proper planning. For example, minor drips of reactive stain can be obliterated success-fully by immediately rubbing them into the surrounding wet stain. Drips of pigment or dye, however, should be left to be address after the main field has dried. Mixtures for new construction should be designed to produce a slab ready to accept subsequent stain treatments.

6.2.2 Application—There are several methods of applying reactive stain. For example, the stain solution can be trans-ferred to the surface and immediately scrubbed in with a bristle brush. Reactive stains may also be applied full strength or diluted using a plastic acid-resistant sprayer with a circular or cone-shaped nozzle to mist in thin applications without scrubbing. Additional methods include sponge, rag, and poultice. When staining steeply sloped or vertical surfaces such as corner returns, applications should start at the bottom and work upward.

Fig. 6.2b—Example of floor treated with reactive stain yielding a mottled effect (courtesy of Concrete Polishing Association of America).

Fig. 6.2c—Reactive stains can be combined with exposed aggregate and polished or unpolished finishes (courtesy of Greg Schwietz).

Fig. 6.2d—Reactive stain combined with exposed aggre-gate and polished or unpolished finishes (courtesy of Greg Schwietz).

Fig. 6.2e—Various locations of a slab can yield different levels of reaction, such as in this case where the same reac-tive stain was applied at the same time. The resulting color difference was due to different concrete batches (courtesy of James Vermillion).







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When using a brush, the full-strength stain solution should be spread over the surface and brushed in until the reaction stops. Maintaining a wet edge, new applications can be made to adjacent areas and worked back into previous appli-cations. The staining reaction is finite so some overlap of identical solutions of wet stain onto areas that have already dried should not result in a visible darkening of the overlap area. Drips, splattering, or puddling should be avoided, as more irregular concentrated discoloration will result.

6.2.3 Residue removal—When the final application of reactive stain has remained on the surface long enough to produce the desired effect, the surface should be washed using a chemical base such as sodium bicarbonate or ammonia, followed by a thorough water rinsing. Test the concrete surface for a pH level that meets the sealer manu-facturer’s requirements before applying sealers.

6.2.4 Techniques and timing—The desired staining effect should be established from mockups and test areas. Depending on the procedures established, multiple appli-cations of the same color or different reactive stain colors are often used for unique appearances. The reacted stain is allowed to remain on the surface or washed off between applications. For quality control, once a desired appearance has been achieved, the same process using the same applica-tion equipment should be maintained, preferably by the same individuals responsible for each task. When applicable, use construction joints, control cuts, scored cuts, or masking as a stopping point.

6.2.5 Advantages—The permanent variegated color effects formed by reactive staining cannot be easily dupli-cated. They are prized in architectural concrete design for producing non-uniform, translucent, mottled, variegated color that allows for the creation of a wide range of unique effects (Fig. 6.2.5). Chemical stains can be used on any cured concrete, old or new, colored or uncolored, interior or exterior, horizontal or vertical. Colors created are consid-

ered permanent and are not soluble in water or common construction solvents. Reactive stains, unlike acrylic stains and concrete coatings, will not surface craze, chip, or peel.

6.2.6 Disadvantages—The disadvantages of reactive stains include: color limitations, blemishes, color longevity, and low reactivity (Fig. 6.2.6).

6.2.6.1 Color limitations—When color is produced from chemical reactions versus the use of pigments, the color range is limited to metal earth tones that are somewhat trans-parent. The colors obtainable by reactive stains will typi-cally include black and shades of rust brown, golden brown (iron oxides), and green/blues (chromium oxides) resem-bling earth tones. Some colors for interior use only are not UV-resistant. The colors created do not cover imperfections in the concrete surface. In many instances, existing imper-fections are exaggerated by staining, which can be consid-ered an advantage if the owner and designer/engineer are aware of this characteristic of reactive stains.

6.2.6.2 Blemishes—If the chemically stained surface is chipped, gouged, cracked, or spalled, the uncolored concrete below is exposed. Generally, stain repairs are difficult to replicate exactly. However, with care and an experienced applicator, stains can be blended into the existing work to minimize the damaged area’s appearance. Patching should be accomplished with cement, sand, and silica flour to create a permeable, well-graded patch without polymer modifiers. Pigments dissolved in solvents can be effective in repairing blemishes in areas that do not react or take on the desired appearance with reapplication of chemical stains.

6.2.6.3 Color longevity—When exposed to traffic, the surface of chemically stained flatwork will gradually abrade, and wear paths can appear if the surface is not adequately protected by sealers or adequate densification and hardening. Reapplication of staining materials to the abraded areas usually does not produce satisfactory color results. Abrading of chemically stained concrete surfaces can be avoided or reduced by maintaining the surface appropriately. Stains are not recommended for vehicular traffic areas.

Fig. 6.2.5—Chemical stains are permanent, one-of-a-kind features that can be highlighted by engraving pattern outlines (courtesy of Concrete Mystique Engraving).

Fig. 6.2.6—Reactive stain employed in this restoration project has a variable effect based on paste volume and slab condition (courtesy of James Vermillion).







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6.2.6.4 Low reactivity—Some concrete cannot be chemi-cally stained and is considered unstainable by this method. If the necessary reactive components have been leached from the concrete by competing reactions, for example, acid washing or exposure to weather or wear, no reaction can take place and no satisfactory color will be obtained. As outlined in 3.6.2, the inclusion of some supplementary cementitious materials (SCMs) alter the concrete’s ability to react with staining materials, as they use up a significant portion of the calcium hydroxide required for a reaction with the stain. Some polymer-modified mixtures also tend to reject acid stains. Some penetrating sealers inhibit stains from reacting. A water penetration test should be performed to observe whether the concrete surface can accept a reactive stain. Burning with a power trowel can make a surface difficult to stain. In these cases, sanding with an aggressive sanding pad often opens the cement paste surface sufficiently to accept a reactive stain.

6.2.7 Special procedures and tools—The following tools can be used on a typical reactive staining project:

(a) A floor cleaning machine or orbital scrubber(b) Pole-mounted acid brushes, mops, plastic, or acid-

proof buckets for rinsing(c) Power-washing unit(d) Acid-proof sprayer(e) Wax applicators(f) Clean rags, sponges, layout tools, and painter’s tape(g) A small grinder with a diamond bladeFor large-area applications, use long-handled, acid-resis-

tant, stiff-bristled brushes to scrub the stain into the concrete surface. The chemical stain can be transferred to the surface using the same brushes and an acid-resistant, wide-mouthed plastic pail, or with an acid-resistant hand-pump sprayer. Scrubbing is accomplished in smaller areas or secondary accent staining with mops or other implements. Mechanical scrubbing is not always necessary or appropriate, depending on the surface effect desired.

As previously noted, sealers should be applied to protect stained finishes. Due to their ability to apply liquids uniformly, airless sprayers and microfiber mops are two of the commonly preferred methods for applying clear sealers to a decorative surface. Other equipment, such as hand-pump sprayers, rollers, or brushes, make uniform applica-tion more difficult.

6.2.8 Required products—Applying abrasion-resistant sealers or coatings and maintaining them is important. Chemically stained concrete should be either densified and hardened or coated to protect the surface from abrasion, discoloration, and unintentional staining caused by expo-sure to weather and everyday use. Clear coatings can cause color variations in the chemically stained surface to be more apparent, accentuating the contrast. Solvent-borne sealers tend to darken the surface, whereas waterborne sealers typi-cally produce little or no change in the final color.

The stains themselves do not affect abrasion resistance. Sealers provide the wearing surface and protection for the artistic features below them. For this reason, sealers should be high-performance and properly maintained to ensure

longevity of the finish. High-performance waxes applied over sealers are a good, inexpensive method to blend out wearing marks and provide an additional easily renewable wearing surface.

Some chemical stain manufacturers market a clear sealer intended for use over chemically stained concrete. The clear sealer should be compatible with the chemical stain and resistant to abrasion, weather, ultraviolet rays, and contami-nants that might come in contact with the surface. Contami-nants might include oil, grease, food spills, and deicing salts, depending on the in-service requirements.

Application of sealers can cause color removal and streaking if the sealer is soluble in the same solvents as the pigment or dye. If they are mutually soluble, then sealant application should only be sprayed instead of rolled or brushed.

6.2.9 Safety considerations—Reactive stains contain corrosive materials and care should be taken during trans-porting, storage, handling, and use. Appropriate personal protective equipment should be worn, including splash-resistant safety goggles, boots, gloves, and other protective clothing. The work area should be properly ventilated. Acid-neutralizing eye wash should be kept at hand when handling or applying reactive stain.

Runoff can damage plants or discolor surrounding areas. It should be picked up with a wet vacuum, absorbed with an inert material, and vacuumed or swept up or wiped up with rags.

When applying acetone-based materials, it is critical to maintain proper ventilation and the elimination of open flames, sparks, or other ignition sources to prevent flash fires. Acetone-based materials require close adherence to manufacturer’s safety information recommendations, local code requirements, and OSHA regulations. For example, respirators fitted with organic vapor cartridges are often required in application of these materials.

6.3—Concrete dyesConcrete dyes solutions use solvents or other carrying

agents to penetrate into the capillaries of concrete and can be used to achieve a variety of colors in hardened concrete. Concrete dyes can be applied with a brush, roller, sprayer, or other means acceptable to the manufacturer. Most dyes require the concrete surface to be opened by mechanical abrasion or acid etching.

Concrete dyes provide replicable coloration and are not dependent on the reactivity of the concrete. Dyes can dete-riorate when exposed to ultraviolet light. The solvents used to carry some dyes are flammable and potentially explosive.

A solvent-resistant sprayer and mixing vessels are needed when using concrete dyes. Appropriate personal protective equipment should be worn, including boots, gloves, and other protective clothing. The work area should be properly ventilated.

6.4—Acid etchingAcid etching is often confused with acid staining. It is a

permanent process of dissolving portions of the cement paste of a concrete surface. It is used with or without any color to create varying degrees of surface roughness and to create







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artistic patterns. It can also be used to remove a portion of the cement paste to enhance an area or prepare that treated area for a different color or stain type.

CHAPTER 7—POST-PLACEMENT TEXTURING AND PATTERNING TECHNIQUES

7.1—GeneralPost-placement texturing is defined as any surface treat-

ment applied to cured concrete that alters or changes the existing surface texture, resulting in a new decorative feature. Typical applications include ground and polished concrete, sandblast stenciling, engraved concrete, saw-cutting, and concrete scoring (Fig. 7.1a through 7.1e). Proper installation specifications are critically important for polished concrete. Successfully achieving the intended design requires careful consideration of the installation specifications.

7.1.1 Mockup panels—Mockup panels for projects that use post-placement texturing should conform closely to the timing, sequence, materials, and methods to be employed on the finished work. Careful planning should be given to the creation of mockup panels that propose achievable levels of densification and protective treatment in the finished work. Alternatively, they can be used to demonstrate more than one treatment, such as depth of grind, to give the owner or architect/engineer, or both, the options for final selection.

7.1.2 Environmental impacts—Post-placement texturing produces no negative impacts to the environment; however, any residual cement dust and silica particles should be collected for proper disposal. Most polishing dust collec-tion systems include high-efficiency particulate air (HEPA) filtration that, when well maintained and properly operated, can remove over 99.9 percent of airborne particles at a size of 0.3 micrometers or larger. Where appropriate, slurry can be substituted for lime addition in soils requiring lime treat-ment due to excessive natural acidity. This may qualify for environmental credit due to reduction or elimination of delivered lime for landscaping.

7.1.3 Safety—General safety sections will be included with each application as discussed. With most typical appli-cations, dust collection equipment is used to prevent parti-cles from entering the local environment. This will include cement dust and silica particles. Respirable crystalline silica particles are carcinogenic.

Fig. 7.1a—Ground and polished floors yield a durable, long-lasting finish and feature a variety of aggregate expo-sure and polishing options (courtesy of Building Solutions).

Fig. 7.1b—High-profile projects are good candidates for ground and polished floor applications (courtesy of Diamond Designer Concrete Inc.).

Fig. 7.1c—Engraving sets off the dramatic design of this decorative concrete floor (courtesy of Concrete Mystique Engraving).







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7.2—Ground and polished concretePolished concrete is an architectural finish that combines

the use of diamond grinding, honing, and polishing to produce a smooth surface that is durable, light-reflective, and easy to maintain. Some typical uses for polished concrete include schools, airports, retail spaces, casinos, restaurants, warehouses, manufacturing buildings, hospitals and medical facilities, office complexes, public libraries, and other public use areas subject to high foot traffic.

Almost all new and old concrete can be improved and turned into a decorative and long-lasting final finish by mechanically diamond grinding and polishing the surface. When reactive stains, pigments, or concrete dyes are appro-priately employed, the polished concrete can be artistically manipulated into an infinite number of designs. Stencils and free-hand artistry can be used to place logos and original artwork in combination with polishing (Fig. 7.2a). Inlays and inclusions can be installed at the time of concrete place-ment or cut and installed in the slab post-placement (Fig. 7.2b through 7.2e). A wide variety of surface effects and appearances are achievable dependent in part on the condi-tion and flatness of the slab.

7.2.1 Advantages—Polished concrete has the lowest maintenance costs of any existing final floor finish. Polished concrete also provides a floor that is readily amenable to future change in use with minimal change in prepara-tion. Polished concrete lends itself to artistic inclusions

that installed either into plastic or hardened concrete then polished to provide elegant art underfoot.

Fig. 7.1d—Ground and polished existing floor with dye (courtesy of Diamond Designer Concrete, Inc.).

Fig. 7.1e—Before and after photos of a renovated historic custom house now a museum gallery (courtesy of Diamond Designer Concrete, Inc.).

Fig. 7.2a—Engraving sets off the dramatic design of this decorative concrete floor (courtesy of Concrete Mystique Engraving).







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7.2.3 Disadvantages—The upfront cost of polished concrete can be higher initially than other floor surfaces. Polished concrete is susceptible to damage by acid and oil if not additionally protected by a coating.

7.2.4 Process—Polished concrete is achieved by sequential mechanical abrasion. The process is divided into two phases. The first phase is an initial coarse abrasion of the concrete, called grinding (Fig. 7.2.4a). The purpose of grinding is to flatten the surface of the slab to permit fine polishing of the surface, to intentionally expose aggregates within the concrete, or both (Fig. 7.2.4b). The intended amount of aggregate exposure is described as “class of grind.”

The second phase is finer abrasion, termed “polishing.” The purpose of polishing is to completely remove the abra-sive marks of grinding and achieve the specified level of gloss.

The grinding and polishing process can be successfully performed with or without the use of water. All polished concrete exhibits significantly enhanced durability and wear resistance when properly and thoroughly densified. Recom-mended practice is to specify both the class of grind and level of gloss. A complete description of design intent is phrased as Class X, Level Y; for example, Class B, Level 2. Classes of grind range from 0 for burnished and A to D describing increasing levels of exposure of the concrete matrix. Gloss levels range from 0 to 4; Level 0 has no to low gloss, Level 4 has very high gloss. Note that achievement of the design intent is largely dependent on the condition of the slab. If

Fig. 7.2b—This inlaid aluminum swan in natural concrete is an example of a metal inlay featured in ground and polished concrete (courtesy of James Vermillion).

Fig. 7.2c—Embedded aluminum sprockets in floor repair (courtesy of James Vermillion).

Fig. 7.2d—Polished restoration with glass inlaid repairs and dye (courtesy of James Vermillion).

Fig. 7.2e—Polishing accentuates color and contrast in this restoration project. The repair section used a dark stain and special glass aggregate inlays to mask previous office wall sill plate locations (courtesy of James Vermillion).






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the concrete was not installed properly, meeting the design intent may require removal and replacement or an overlay (Fig. 7.2.4c). Where FF values are included, it is better to have values above the minimums specified.

7.2.5 Class of grind—The class of grind describes the amount of visible aggregate exposure resulting from initial grinding and is a result of the amount of surface material removed. Multiple passes with grinding equipment may be necessary to achieve a particular class of grind.

(a) Class 0—Burnished (Fig. 7.2.5a): no significant removal of surface material. Burnishing is applicable to smooth surfaces only, as no significant surface material will be removed.

(b) Class A—Cream: minimal exposure of the fine aggre-gate. This requires concrete placement at or above FF-70. The high FF requirement of the initial concrete placement is critical to maintain a uniform appearance while minimizing exposure of aggregates.

(c) Class B—Salt and pepper: exposure of the small aggregates. This yields a worn, industrial look. Concrete placement at or above FF-45 is needed to maintain a uniform appearance while minimizing exposure of larger aggregates.

(d) Class C—Medium aggregate: exposure of mid-range aggregates. All surface paste is removed with grinding. Concrete placement at or above FF-35 is recommended (Fig. 7.2.5b and 7.2.5c).

(e) Class D—Large aggregate: exposure of the coarse aggregates similar in appearance to terrazzo. All surface paste is removed with grinding. Concrete placement at or above FF-25 is recommended (Fig. 7.2.5d and 7.2.5e).

Aggregate exposed when grinding a slab will be random in size and location, varying with placement techniques, curling, and flatness. Random exposure is beyond the control of the grinding operator, as it is inherent and unique to the slab. Attempts to achieve uniformity by deep grinding where aggregates are ground below their equators can cause

Fig. 7.2.4b—Large aggregate exposed with 25-grit metal-bond diamonds. Note grit scratch pattern on the floor surface (courtesy of James Vermillion).

Fig. 7.2.4c—Ground and polished concrete can reveal irreg-ular aggregate compaction (courtesy of Concrete Polishing Association of America).

Fig. 7.2.4a—Operator performing grinding, which is the first phase in the polished concrete process (courtesy of Diamond Designer Concrete, Inc.).







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slab damage due to aggregate popouts. Acceptable aggre-gate exposure is up to 0.5 times the diameter of the mid-size aggregate in the mixture or 0.5 times the diameter of the seeded aggregate, whichever is smaller.

For new placements intended to display reasonable uniform amounts of exposed aggregates, considerations should be given to intentionally and carefully seeding the surface with aggregates to be exposed. Such seeding can reduce overall cost and increase uniformity of aggregate exposure.

7.2.6 Level of gloss—The term “level” is relative to the gloss attained after polishing is complete. Level indicates the gloss of the uncoated polished surface. Using a specific grit does not guarantee achieving the desired level of gloss; grit is only a descriptor of the tooling commonly used to attain that gloss.

Subjective gloss assessment varies from one person to another. The use of a gloss meter is necessary to accurately assess the spectral gloss of a sample that will be reproduced.

Fig. 7.2.5a—Concrete finish transitions from ground and polished in foreground to burnished and polished in back-ground (courtesy of James Vermillion).

Fig. 7.2.5b—Class C, Level 3 polished concrete (courtesy of Concrete Polishing Association of America).

Fig. 7.2.5c—Class C, Level 3 polished concrete (courtesy of Concrete Polishing Association of America).

Fig. 7.2.5d—Class D, Level 3 polished concrete with fiber in mixture (courtesy of Diamond Designer Concrete, Inc.).






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Thereafter, the same gloss meter and technique should be used to assess the gloss of the final floor. Random, dispersed sample gloss measurements are necessary to establish a statistically accurate assessment of gloss on a floor. The sampling method, protocol, and standard deviation for measuring gloss should be agreed upon by all parties before the work begins. It is always a good practice to demon-strate the final result by building a mockup panel that can be approved by the owner in advance of the project start date. The grit numbers cited in the following level descrip-tions are only a general guide to the grit required to achieve the gloss of that level. Porous or weak concrete, carbonated concrete, or concrete with soft porous aggregates may never be able to achieve high gloss values with simple polishing. Gloss levels:

(a) Level 0—No to low gloss, flat appearance, and a spec-tral gloss below 15. This is usually attained using tools of less than 200 grit.

(b) Level 1—Low gloss, satin, or matte appearance and a spectral gloss within the range 15 to 29. This is usually attained using 400-grit tools.

(c) Level 2—Medium gloss, satin, or matte appearance, diffused reflection of and a spectral gloss within the range 30 to 49. This is usually attained using 800-grit tools (Fig. 7.2.6a).

(d) Level 3—High gloss, clearly reflects objects and a spec-tral gloss within the range 50 to 60. This is usually attained using 1500-grit and finer tools (Fig. 7.2.5b through 7.2.5e).

(e) Level 4—Very high gloss, sharp mirror-like reflec-tion of objects and a spectral gloss above 60. This is usually attained using 3000-grit and finer tools (Fig. 7.2.6b).

7.2.7 Burnished uncoated concrete—Post-placement burnishing is an alternative to the two-step grind-and-polish method of achieving a gloss on concrete surfaces. It is constrained to slabs that are well troweled and smooth. The as-cast concrete surface is polished using abrasive pads. It provides another option to grinding when floor FF flatness is below that necessary for the avoidance of excessive varia-tion in aggregate exposure. Properly performed with densifi-

cation, it can deliver durability benefits and can be an attrac-tive alternative to grinding and polishing.

Burnishing uses fine-grit abrasives to impart gloss when no significant surface material is removed. Gloss Levels 0 to 2 can typically be achieved with this technique. It is speci-fied using the same grading system as ground and polished concrete with class of grind specified as 0. No corrective grinding or repair is possible with burnishing equipment and techniques.

7.2.8 New slab installations—New slabs should include consideration of at least these details before grinding and polishing are performed:

(a) concrete mixture design(b) subbase preparation(c) vapor retarders(d) jointing and joint filler material(e) aggregate selection(f) FF and FL numbers(g) finishing practices(h) curing method(i) quality control(j) post-placement slab protection(k) waiting period or concrete maturity level.

Fig. 7.2.5e—Class D, Level 3 polished concrete with fiber in mixture (courtesy of Diamond Designer Concrete, Inc.).

Fig. 7.2.6a—Class A, Level 2 colored polished concrete (courtesy of Concrete Polishing Association of America).

Fig. 7.2.6b—Class A, Level 4 natural polished concrete and polishing equipment (courtesy of Concrete Polishing Asso-ciation of America).






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7.2.9 Concrete mixture designs—When specifying a concrete mixture, carefully consider the design for ground and polished floors to ensure the concrete mixture design meets all of the intended requirements for floor use. Most standard mixture designs are sufficient for ground and polished concrete if they meet basic requirements, including:

(a) Compressive strength—4000 psi (28 MPa) or greater 28-day strength is ideal for polishing. Low-strength mixture designs are not good for ground and polished finishes, as the concrete will not be durable enough to handle the stresses involved with the grinding and polishing process. If concrete is too weak, aggregate rips and tears from the surface, causing aesthetic concerns and creating additional work in patching or filling.

(b) Cement replacements—Limit the use of pozzolans, such as fly ash and slag cement, to 20 percent or less. Fly ash particles are highly abrasive, causing increased diamond wear and tooling expense. These materials limit the amount of Ca(OH)2 available for the chemical reactions needed for densification or reactive stains.

(c) Aggregates—Along with the aggregate included in the mixture design, the finished floor may require the addition of specialty aggregates that are seeded into the surface (Fig. 7.2.9a). The particle size and shape are important consider-ations, as the aggregate seeded into the surface should be compatible with the mixture aggregates without any signifi-cant impact on strength or durability. For example, smooth or tumbled aggregates have a nice look and feel but may not bond properly with the cement paste. Smooth aggregates can be used provided the depth of grinding does not expose them more than one-half times their diameter. Irregular-shaped aggregates tend to interlock better with the other constitu-ents in the mixture.

Aggregate selections include natural aggregates, synthetic aggregates, nonreactive glass aggregates or particles, metallic particles, or embedments (Fig. 7.2.9b). Steel embedments should be avoided, as they will not grind at the same rate as the concrete and can damage tooling.

(d) Air content—Air-entrained concrete should not be used for hard-troweled concrete finishes, as there is an increased risk of delamination and blistering on the surface. This is referenced by ACI 302.1R and ASCC (2003).

(e) Fibers—Floors reinforced with synthetic fibers can be successfully polished, even with heavy doses. Fiber reinforcing can reduce shrinkage and curling, although maximum gloss potential is slightly reduced. When fibers are included in the design mixture, they will be noticeable on a floor with a Class A grind and sometimes on a Class B grind (Fig. 7.2.9c). Avoid steel fibers if the slab is to be colored using a reactive stain.

7.2.10 Finishing practices—The overall quality and dura-bility of the slab will be affected largely by the finishing practices used during construction (Fig. 7.2.10). The use of ACI-certified flatwork finishers for slab construction should ensure that the quality is consistently high.

Finishing practices include screeding/striking the slab to grade; checking rod and periodic rechecking for flatness,

Fig. 7.2.9a—Polish concrete featuring inlaid and natural stone (courtesy of James Vermillion).

Fig. 7.2.9b—Specialty aggregate yields unique finishes (courtesy of L. M. Scofield Company).

Fig. 7.2.9c(a)—This mixture contains a medium high to high dose of macrofibers and is ground to Class A, Cream. Note that fiber marks are visible (courtesy of Diamond Designer Concrete, Inc.).






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which is critical when top-seeding aggregates; edging for flatness and tooling; edge tooling; proper floating; hand floating after initial floating; troweling; proper timing for each process; and curing. When seeded aggregates are to be used, refer to ACI 302.1R for guidance.

7.2.11 Tolerances—For the purpose of ground and polished concrete, the FF number has the most significance, as a flatter surface will grind and polish easier with more control over the final appearance. For example, if a specifi-cation reads Class B, Level 3, the specified finish could not be achieved with a Flatness F-Number of FF-35 or lower. The result would be a floor with Class C in all the high spots and Class A to B in all of the low areas. For the best results, an FF number equal to or greater than that recommended for the class of grinding specified is recommended when specifying a ground and polished finish. Specifying higher flatness values than required for the class specified does not inhibit achievement of the specified final finish.

7.2.12 Jointing—Properly installed joints are critical for a successful ground and polished project. The joints should be installed in accordance with ACI 302.1R. The recommended method is use of an early-entry saw to saw cut the joints using a dry-cut blade with a vacuum attachment. If the joints are filled too early, there is significant risk of joint failure due

to slab shrinkage. There is also the risk of joint sealant pene-tration into the slab adjacent to the joint, creating a release seal that will not accept a reactive stain or dye. The timing of joint filling should be considered with respect to the type of product used and advantages and disadvantages of early and late joint filling.

7.2.13 Existing concrete slab considerations—Polished concrete can be successfully achieved on most existing slabs. Proper evaluation is necessary to determine what considerations will affect the polishing process and outcome for the intended use of the floor. Some common consider-ations include:

Fig. 7.2.9c(b)—This mixture contains a medium high to high dose of macrofibers and is ground to Class B, Salt and Pepper. Note that fibers are minimally visible and that this is the same floor as Fig 7.2.9b(a) (courtesy of Diamond Designer Concrete, Inc.).

Fig. 7.2.9c(c)—This mixture contains a high dose of macro-fibers and is ground to Class D, Large Aggregate. Note that fibers are not visible (courtesy of Diamond Designer Concrete, Inc.).

Fig. 7.2.10—Exposed aggregate showing installation screed line (courtesy of James Vermillion).






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(a) Floor use history to consider possible contaminants in the concrete matrix

(b) Existing coating removal, including curing, sealer, or adhesive compound removal

(c) Floor moisture transmission levels(d) Penetrations or bolts(e) Crack repair(f) Slab porosity and hardness(g) Slab curl(h) Flatness and levelness(i) Joint treatments and sealants(j) Presence of contaminants, such as oil7.2.14 Required products: densifying systems—Under-

standing the basic concrete chemistry of densification is a key component to the success of a ground and polished application. Typical densifiers are silicate-based products that react with the surface to produce additional calcium sili-cate hydrate (C-S-H) gel. Other products contain siliconates, which are also used for the protection of concrete. Silicate- and silicone-based products are different component chemi-cals that react differently with the concrete once applied. Figure 7.2.14 offers a basic understanding of this chemical process.

The main difference in silicate products is typically the carrier used to carry the silicate into the substrate. These are most commonly sodium, potassium, and lithium.

Although all three types provide distinct advantages and disadvantages, it is important to understand a few basic points about them when making a selection for a specific project. Some products blend silicates and siliconates together to provide a multipurpose product. Whichever densifier is selected, understand that the harder the surface, the higher the gloss level and the longer wear that will be achieved. Read the manufacturer’s literature carefully and conduct relevant installation testing before choosing a densi-fying product.

The following (7.2.15 through 7.2.20) are basic criteria to use when selecting densifying products. All of them are suit-able for ground and polished concrete floors.

7.2.15 Sodium surface densifier—Used on floors both with and without color, sodium surface densifiers, which have been used for more than 60 years, are the most often used on commercial, architectural, and industrial floors. They are also used for chemical polishing or burnished projects.

7.2.16 Potassium surface densifier—Typically used for architectural concrete where color is applied, potassium surface densifiers are also used on commercial and indus-trial floors and for chemical polishing or burnished projects.

7.2.17 Lithium surface densifier—Typically used for architectural concrete where color is applied, lithium surface densifiers are also used on commercial and industrial floors and for chemical polishing or burnished projects.

7.2.18 Pigmented densifiers—Relatively new to the marketplace, few long-term examples of pigmented densi-fiers are available. Selection of this type of product should be done based on the carrier and the densifying properties the product provides. Many of these manufacturers recommend a coating used in conjunction with the pigmented densifiers.

7.2.19 Safety—Safety requirements for ground and polished concrete vary depending on the individual stages of the process. For example, during the grinding stages, dust extraction equipment should be used if dry grinding. Particle masks (P95 or P100) should be worn by machine operators and their assistants if any dust is present in the atmosphere and during tool changes. Hearing protection should also be worn where appropriate. Protective boots, gloves, and other clothing should be worn at all times.

7.2.20 Sustainability—Ground and polished concrete is a sustainable flooring surface due to its enhanced aesthetic appeal and durable low-maintenance finish. The improved reflectivity of polished finishes can lead to reduced energy costs for lighting. Polished floors contribute to indoor envi-ronmental quality because they do not harbor dust or provide a food source for mold or mildew.

7.3—Sandblast stenciling (abrasive blast stenciling)

Using durable protective materials while blasting away the exposed concrete surface of plain or surface-colored concrete

Fig. 7.2.14—Comparison of reaction of silicate- and silicone-based products.






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creates patterns with texture and color. Free-hand media blasting is used for intricate decorative effects and touch-up repairs. Several blasting media are available, including silica sand, blast slag, metal shot, and glass blasting media. Typical applications include large or small custom logos, exposed surface texture, textured bands for color variance, and textured areas for safety or pedestrian traffic.

7.3.1 Special procedures and tools—Concrete require-ments vary depending on the specific application and desired look. It is important the concrete has sufficient strength to handle the pressures created by the blasting equipment. Concrete should have cured at least 28 days prior to blasting operations. If integral colored admixtures have been used, then a mockup panel should be done to determine the effect the blasting will have on the final appearance of the color. Typically, the color will be lighter after the application and, in some cases, completely removed from the surface. If the surface has received a stain or dye treatment, the color will usually be removed in the blasted areas (Fig. 7.3.1a and 7.3.1b). This will create a three-dimensional look to the surface. Recoloring of the blasted areas is common after the mechanical application is complete. If the area has been treated with a color hardener, use care to not completely remove the hardener, or plan for its replacement where removal is unavoidable.

For new placements intended for sandblasting, apply the hardener at a high rate; usually approximately 1 lb/ft2 (5 kg/m2) with a smooth trowel finish applied. Sandblast templates and stencils can also be used on ground and polished surfaces. In these cases, all polishing steps should be completed, except for application of the protective treatment, which can be done after the sandblasted area is completed. In some cases,

the surface finish will be smooth for interior floors or retail showrooms. Sandblast stencils are also applied to textured or stamped concrete. Use a flexible stencil to maintain good contact with the substrate at the edges of the stencil.

7.3.2 Materials and equipment—Portable abrasive blaster (blast pot), air hoses and nozzles sized appropriately for the task, air compressor, blasting media, protective masking for adjacent areas, hardboard or masonite design templates, hard plastic design templates, vinyl or 0.045 in. (45 mil) thick plastic, and safety equipment could be required when sandblasting.

7.3.3 Hard template applications—The steps for applying a hard template are similar to the steps for applying paper stencils, except that a repeating pattern is achieved by repeatedly moving the hard template during application. These templates are non-adhesive and are typically made of high-density plastic materials.

If using a template for a border, make sure that the border is defined using a saw-cut or scored joint to aid in place-ment. The saw-cut or score line should be the same width as the template being used. Applications vary depending on the equipment and type of template used. Fastening the templates in place is recommended to prevent them from moving during the application. Consult the manufacturer’s directions for complete details.

7.3.4 Vinyl stencil application—After the surface has been fully cured and cleaned, the sandblast template is applied. The area should be sealed with an acrylic sealer. This step is optional depending on the project color requirements, but will help in promoting proper adhesion of the stencil.

The stencil mask should be oriented on the surface and checked for proper alignment. If the stencil is larger than one panel or tile, then the panels should be taped together and positioned as one piece.

With the stencil in place, registration marks should be transferred to the surface and the marks should be half on the stencil and half on the surface to be used as a reference point for positioning the stencil during adhesion. These

Fig. 7.3.1a—Layout and preparation for sand-blasted lettering with dye stencils on polished concrete (courtesy of James Vermillion).

Fig. 7.3.1b—Completed sandblasted lettering with dye sten-cils on polished concrete (courtesy of James Vermillion).






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marks should be placed at regular intervals on all sides of the stencil including marks for top, bottom, and center.

Remove the stencil and clean the area completely using isopropyl alcohol, using caution not to remove the registra-tion marks from the previous step.

Starting at one edge of the stencil at the top or bottom, remove 2 to 4 in. (50 to 100 mm) of the plastic sheet covering the adhesive side of the stencil. Carefully align this edge with the registration marks made for the same edge. Using a plastic smoother, set the stencil in place and care-fully remove any air from the adhesive area. This part of the application will require more than one person depending on the size of the template. One or more persons should be holding the template in place above the area while another one or two persons gently pull back the plastic adhesive sheet. When pulling the protective sheet, the angle of pull should be perpendicular to the surface. As the sheet is pulled back, the stencil is laid in place using the plastic smoother, keeping the registration points lined up, and removing any air bubbles that form. This process should be continued until the entire template has been placed and any air bubbles have been removed.

The use of an open flame torch or heat gun may be required to achieve proper adhesion of the stencil to areas that are textured. Any traditional finish will suffice for receiving a sandblast treatment as long as the surface is durable and fully cured. After removal of air bubbles, the stencil should be burnished to the surface before removal of the protective scrim.

The top protective sheet is then removed and the stencil weeded for blasting. Proper sections of the stencil should be weeded to create either a positive or negative impression. When positive areas are removed (weeded), the decorative treatment is applied to the open areas to produce a posi-tive design; negative weeding removes the areas around the desired pattern, making the treated areas contrast with the masked-off design. This is typically decided in advance of the stencil application. After the stencil has been weeded, the edges should be checked to ensure good contact. Heat may be required to aid in adhesion. The edges should be masked for additional protection of nonblasted areas.

7.3.5 Finishing requirements—The sandblasted area will typically be a smooth surface or smooth trowel finish. For exterior applications, additional texture may be required to meet sufficient slip coefficient numbers (slip coefficient of friction). In extreme cases, stamped or textured concrete is sandblasted for specific design requirements such as logos or surface markers.

Apply sandblasting to the exposed areas, moving in a smooth and consistent manner. The tip should be held approximately 4 to 6 in. (100 to 150 mm) from the surface. Blasting should be continued until all exposed areas have been treated consistently. Proper safety equipment should be worn at all times.

Sweep or vacuum the area before removing the stencil. Check the area again for consistent exposure and reblast where needed. Apply any required additional stains or colo-rants before the stencil is removed. After completion of

sandblasting and additional coloring, the stencil is removed and discarded. The area should now be cleaned and properly sealed before use.

7.3.6 Safety—Any time sandblasting is being used, there is a constant danger from exposure to silica particles from the blasting media and from the blasted substrate. Proper respi-rators should be worn with cartridges approved for dust and airborne particles. Protection from the blasting material and forced compressed air should also be considered. Protective clothing heavy enough to resist the blasting pressure should be worn at all times, including heavy gloves, jeans, protec-tive coat or long-sleeve shirt, eye protection, and a full face shield mask.

7.3.7 Sustainability—Given the same performance and safety characteristics, the use of recycled materials as the blasting media for sandblast stenciling is environmen-tally preferable to using virgin raw materials. Sandblasted finishes are deeply etched into the concrete surface and will require less maintenance than other surface coating mate-rials or concrete finishes where abrasion resistance is key.

7.4—Engraved concreteDecorative concrete engraving is the act of modifying

existing (cured) concrete by cutting patterns and texture into the surface. Engraved designs and patterns simulate building materials such as brick, tile, stone, pavers, or a variety of other graphic elements (Fig. 7.4). Geometric patterns with straight, circular, or serpentine lines and custom designs are cut directly into the surface of the concrete. Decorative concrete engraving adds depth and dimension. It is also used as a color separation technique.

7.4.1 Typical applications—Concrete engraving is often used in artistic applications or designs. The technique is used to restore old or uncolored concrete. Using the design tools and templates to create a pattern or texture on the surface can bring a new look to existing concrete. The addition of color and reactive stains or dyes also aids in creating a unique and custom look. Concrete engraving is ideal for specialty logos for retail or resort projects, theme parks, and public-use

Fig. 7.4—Engraving highlights the design of this exterior patio (courtesy of Concrete Mystique Engraving).






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areas subject to high foot traffic, including warning symbols or textures. From tile-patterned flooring to original artistic designs and graphics, engraved concrete can be used for creating numerous textures and patterns. Engraved concrete is also ideal for restoration or makeover projects for vintage concrete.

7.4.2 Concrete requirements—The specific concrete requirements will vary with the application. For example, saw-cutting for control or jointing should be done as soon as practical to prevent cracking in the paving section. If engraving is being done and clean precision cuts are required, waiting for the slab to be fully cured to 3500 psi (24 MPa) or higher is recommended to reduce spalling on the edges. Engraving and coloring on the same slab typi-cally would require that the slab is fully cured to produce the best results. Needlepoint tools severely impact the surface with a very high point load. Concrete surfaces of insufficient strength will experience spalling or microfractures of the substrate, creating a surface more prone to premature wear and damage from freezing and thawing.

Coloring of the cured concrete surface before engraving is typical. Coloring is accomplished by use of a variety of chemical agents, although reactive stains, concrete dyes, and pigments are the most common.

7.4.3 Special procedures and tools—Decorative engraving can be accomplished with many different tools, often adapted from other trades or originally designed for other purposes. Commonly used tools include grinders, diamond blades, crack chasers, needle scalers, vibratory tools fitted with diamond or silica carbide tooling, layout equipment, straight edges, chalk line, soap stone, nonstaining chalk, radius cutting tools or equipment, and hard templates or dies for patterns (Fig. 7.4.3). Concrete engraving tools, whether they are pneumatic or electric, cut the surface with various methods including abrasive diamond blades, sandblasting, shotblasting, micro-rod impaction, and reciprocating stylus. Tools can be used in combination with design templates to achieve exacting graphics and artistic results. Templates can be made of a variety of materials, including single-use adhesive-backed vinyl or reusable nonmarking plastic. Engraving tools can be controlled with tracking systems to make perfect circles, arcs, or straight lines or to efficiently produce patterns such as brick. Intersecting lines and graphic elements are easily controlled with precision tools that have appropriate cutters.

The bottom of the engraved area can be as visually impor-tant as the surface, possibly making accurate depth control essential. Engraved kerfs (cut or incision) range from very narrow to very wide, depending on the design parameters. Kerf depths are typically 1/16, 3/32, or 1/8 in. (1.5, 2.4, or 3 mm) deep. The depth of the engraved lines can be purely aesthetic or functional. Deeper engraving is required to hold sufficient amounts of an epoxy or grout in the recessed area.

Dust control, for many reasons, is a necessity. All tools should be fitted with dust control and high-efficiency partic-ulate air (HEPA) dust extractors that have adequate airflow for prevention of respirable silica escape. Most engraving tools have shrouds and guards that attach to standard shop

vacuums. Pneumatic tools have combination water/vacuum dust control.

7.4.4 Finishing requirements—Finishing requirements for engraving are the same as other decorative concrete. Existing concrete should be thoroughly cleaned before processing. Any traditional finish can be engraved, including stamped concrete, broom finish, smooth trowel, and salt finish. The only finish not recommended for engraving is an exposed aggregate finish.

7.5—Decorative saw-cutting (scoring)Saw-cutting is traditionally used for contraction joints

or early entry cuts to aid in crack control. Decorative saw-cutting, also known as scoring, is not intended for contrac-tion joints. The placement and pattern can allow for score joints to coincide with cracking contraction jointing. Score joints do not have to be cut as deeply as contraction joints and normally do not create a weakened plane in the concrete. Decorative saw-cutting can be used:

(a) To pattern concrete, create a border or bands, or enclose decorative features

(b) As a decorative feature or texture(c) To keep post-placement color from bleeding into adja-

cent colors(d) To define shapes such as grid patterns for floors,

borders, or cross bands(e) To define features and create artistic abstracts7.5.1 Special procedures and tools—Scoring can be simply

yet effectively done by a skilled tradesman using basic tools such as a circular saw or an angle grinder with diamond or abrasive masonry blade. Saw-cutting can be used on colored or uncolored concrete, textured concrete, or any traditional or specialty finish. Early-entry dry-cutting saws allow the slab to be cut before the formation of shrinkage cracks. Such cutting requires the slab to be cut completely within 24 hours of initial set. Refer to ACI 302.1R for further guidance.

The cutting process historically required water as a coolant, although modern saws are able to make excellent dry cuts. Maximum 1/8 in. (3 mm) wide kerfs are standard, although

Fig. 7.4.3—Crack chaser with vacuum shroud (courtesy of James Vermillion).







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1/4 in. (6 mm) is used in those cases where a colored grout or sealant is used to offset an object within the saw-cut pattern. When scoring patterns are used, the width of the contraction joints should be made with similar equipment and blades. Accurate depth control is limited and largely dependent on the flatness of the surface. Straight unwavering lines require highly skilled operator(s) and saw guides.

Gasoline-powered saws are typically only used outside because of carbon monoxide and carbon dioxide emissions from the engine. Used without adequate ventilation, either carbon gas can be hazardous to the operator and can cause surface damage to the concrete slab by chemical reaction or carbonation of the slab surface, reducing its strength and fitness for decorative treatment.

CHAPTER 8—DECORATIVE OVERLAYS AND REPAIR METHODS

8.1—GeneralDecorative overlays are versatile products that can be used

in new construction or as a repair method. They can create long-lasting and durable new surfaces and are an alterna-tive to removal and replacement of old or damaged concrete. Some overlay materials are self-leveling or spray-applied as thin as 1/16 in. (1.5 mm) up to 1/2 in. (13 mm) or more. During installation, overlays can be artistically embellished by use of inlaid inclusions, integral color, stenciling, and surface texturing or patterning. Subsequent to installation, some overlays can be diamond polished, dyed, and or chem-ically stained.

8.1.1 Preconstruction planning—Decorative overlays are high-performance products that require preparation and planning to ensure a quality project. Protection of existing structures and landscapes should be walked through in advance of the overlay installation. Curing protection and temperature constraints require logistical planning of how materials and personnel will be used. Materials should be laid out close to their final destination and placement crew responsibilities for key positions such as mixer, applicator or nozzleman, equipment operator, and finisher should be established before commencing the work.

In any concrete repair scenario, the repair contractor should understand the source of concrete problems to imple-ment a long-term, durable repair. Contractor prequalifica-tion and examples of previous work performed should be reviewed prior to accepting proposals.

8.1.2 Drawings—Drawings of the repairs or decorative overlay artwork are recommended. They identify and call out the work to be done and help define a project’s scope. Good drawings act as a visual guide to the extent and kind of the work to be done. Drawings should include both a plan view and sectional drawings. Vertical work should also include elevation views. The drawings should note the problem areas and concerns such as cracks, joints, and surface repairs. They can be used to create a schedule of work. Once the work has been identified, it is necessary to consider if the intended repair is restricted by building codes.

8.1.3 Sample sections—Sample sections or sample repair sections can be used in a manner similar to mockup panels. They should be used to establish blemish tolerances and can act as training aids. They should include typical patching for scratches, gouges, and popouts to replicate how a repair will be completed. The expense of creating a sample section should be included as part of the owner’s budgeted expense.

8.1.4 Surface preparation—Surface preparation is the key to the durability of the decorative overlay. Surface prepara-tion usually begins with a visual inspection of the project conditions. When using an overlay as a repair, it is essential to understand the conditions that created the need for repair. The original cause of failure should be corrected before the overlay is installed. Investigative observations recorded on a drawing can be extremely valuable in concrete repairs of this type.

Decorative overlays require a solid substrate that is clean and free of debris or material deposits that inhibit bond. All loose materials, paints, curing compounds, and organic growth should be removed in advance of the decorative overlay. Damaged concrete should be removed from sound concrete. All repairs to both vertical and horizontal surfaces should be performed prior to final surface preparations. Defects should be treated and prepared as specified by the overlay manufacturer.

Alkali cleaners remove oil and other hydrocarbon-based materials. Grease or heavy oil deposits that have penetrated deeply into a slab should first be scraped at the concrete surface followed by the application of an appropriate solvent or enzymatic cleaner. Alkali cleaners can remove most organic deposits. Oxidants can remove vegetation stains and mildew. Muriatic or hydrochloric acid cleaners can remove cement dust and thin layers of laitance.

Mechanical surface preparation is typically required to remove the upper surface of the existing slab. This is achieved by diamond grinding, abrasive blasting, pneumatic hammering, water blasting, or a combination of techniques. Prior to working on the portion of slabs adjacent to structural walls, ensure they are plumb and structurally sound.

Chemical removal of slab surfaces is typically labor-inten-sive. It often requires significant measures to protect the environment and necessitates careful cleanup and disposal of materials. However, it can be a cost-effective option on small projects. Consideration should be given to the pH level of the surface after acid-based cleaning and before applying any new coatings.

8.1.5 Cracks—Existing cracks should be noted on the repair drawing by type and location (refer to 8.1.2). Crack visibility and required repair method will vary depending on the specific crack or project circumstances (Fig. 8.1.5a and 8.1.5b). Some of the various materials available for crack repair include methyl-methacrylates, epoxies, polyureas, modified urethanes, and others. Regardless of the material used, it is important to determine if a crack is stable and unsusceptible to dimension changes. Minor cracks that are static, such as plastic shrinkage cracks, can be sealed and topped over without issue. Cracks penetrating the entire concrete section or that are unstable or subject to changes






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in dimension should be routed and finished similarly to contraction joints. These crack types should be accommo-dated by creating a joint in the topping or they could result in an uncontrolled cracking in the overlay above. The owner should be notified of the presence of unstable cracks, as they necessitate creating a visible joint in the topping course.

8.1.6 Joints—Consideration should be given to joints in the underlayment material and in the final overlay product.

Existing joints in the underlayment should be detailed on the drawings by the type of treatment they will receive.

Some joints are stable with very thin or no visible cracks at their base. When created, these joints allow the existing concrete to shrink or move during the placement and curing process. As with minor or stable cracks, these joints can be filled and topped over without issue. Topping over an unstable joint subject to movement or dimensional changes will result in cracking in the topping unless reinforcement or bridging materials are used to restrict movement in the underlying slab. Bridging material selection is a critical concern when making this type of repair. Coefficients of expansion of interfacing materials should be given serious consideration, as differential movement between adjacent or bonded materials can result in uncontrolled cracking. When sealing joints in advance of the decorative overlay, the joint should be masked to prevent bond of the overlay to the sealant. Damaged or eroded joint nosing should be repaired with a cementitious or epoxy material that satisfies the ultimate use of the slab. Work on existing joints should be performed well in advance of overlay applications.

8.2—Special procedures and toolsThe type of spray equipment most manufacturers recom-

mend for applications are low velocity, low pressure, and are either a hopper-gun type or a slurry pump mixer/sprayer combination.

8.2.1 Hopper guns—A hopper gun is a tool that gravity-feeds mortar, coatings, or toppings to a trigger-activated spray nozzle. Material is held in an open top hopper and powered by compressed air. Hopper guns have the advan-tage of being lightweight and portable. They usually output 7 to 10 ft3/min (0.2 to 0.3 m3/min) at 30 psi (0.2 MPa) and require a separate air compressor operating at low pressures. Quality control valves with gauges to ensure their accu-racy and consistency of pressure are essential. The small hopper often requires repetitive filling and mixing of spray materials.

8.2.2 Grout pumps—Grout pumps come in a variety of sizes and have the advantage of larger capacity. They are more appropriate for large projects and can accurately deliver large volumes of material via flexible hoses and or wheeled equipment to quickly convey materials to where they are needed.

8.2.3 Troweling—Lightly troweling freshly applied overlay material can produces a variably smooth top surface with fissures (differential offsets) produced by the random spray pattern. This process also decreases the surface profile, resulting in a smoother overall texture that is referred to as a travertine marble effect. A trowel with rounded ends (pool trowel) eliminates most trowel marks.

8.2.4 Templates—Templates can be used as described in previous sections. Because the overlay materials are sprayed on, however, they can be made of lightweight materials most consistent with post-placement coloring agents. They are either single-use or reusable and are applied to the base coat of the decorative overlay. While some have adhesives, others are held in place by mechanical means.

Fig. 8.1.5b—Integrally colored crack repair with freehand engraved leaves (courtesy of James Vermillion).

Fig. 8.1.5a—Patch repair using artistic technique (courtesy of James Vermillion).







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8.2.4.1 Single-use templates—Single-use templates for decorative overlays are often made of paper that has been punched to the desired configuration. They often come in rolls up to 300 ft (91 m) in length and approximately 3 ft (1 m) wide. Single-use templates are removed after the finish coat has cured sufficiently to prevent damage to this coat. Single-use templates typically have adhesives that allow them to adhere to the underlayment; this gives them the advantage of precise alignment and, if carefully applied, they deliver clean crisp lines of delineation.

8.2.4.2 Reusable templates—Reusable templates are usually made of plastic or steel. They are mechanically fastened or taped in place on the base coat of the decorative overlay and removed as soon as the finish coat has cured sufficiently to prevent damage to the coat. After each appli-cation, they should be cleaned and readied for the next use. They create less waste than single-use templates and their costs can be amortized over several uses. They should be carefully secured in place and aligned with previous pattern markings for each area. When practical, use a ledger or straightedge to ensure consistent alignment.

8.2.5 Tape—Tape can be used to complement either the single-use or reusable templates. Tape can also be used alone to produce a desired effect. Tape is applied to the base coat, the finish coat is then applied, and then the tape removed after the finish coat has cured sufficiently to prevent damage to the coat.

8.3—Required products8.3.1 Topping materials—Only cement-based materials

are addressed in this guide. Thin-sprayed decorative over-lays are often polymer-modified cementitious (PMC) prod-ucts. Polymer modifiers increase bond and impart flexural strength to allow for thin applications. Because formulations of these prepackaged products vary, consult the manufactur-er’s information to select the right product for a given appli-cation. The most widely used polymers for PMC mortars are polyvinyl acetates (PVA), styrene-butadiene resins (SBR), poly-acrylic esters (acrylics), ethylene-vinyl acetate (EVA), and styrene acrylics.

Several of these products are re-emulsifiable up to one or more times both during and after the overlay has cured. They should never be used in damp conditions. Be attentive to information regarding color stability, as some products can discolor over time. Typically, acrylic-based products are less susceptible to discoloration problems than SBR-based materials.

Polymer-modified materials are frequently applied with spray equipment while poured or trowel-applied cementi-tious overlay materials often have similar chemistries.

8.3.2 Mortars—Mortars differ from overlays; they can be formulated on site, are not intended to overlay an entire slab, and can be used to repair spalls or surfaces with deeper damage. Most repair mortars use white cement, white sand, and pigments along with polymers to improve their physical properties. Mortars typically have a higher cement-to-aggre-gate ratio than most concrete, so it is often necessary to mix white and gray cements to achieve an acceptable color match

to the existing concrete color. Multiple test patches should be made and component quantities recorded to determine the appropriate patching materials before starting work.

8.3.4 Quality control requirements—Repair materials can be high-performance products that often require a high degree of quality control in their manufacture. Manufac-turers of prepackaged spray-applied repair materials should periodically test, closely monitor, and report on a variety of performance characteristics, including:

(a) Volume changes according to ASTM C1090(b) Modulus of elasticity according to ASTM C469/

C469M(c) Tensile strength according to ASTM C1583/C1583M(d) Bond strength according to ASTM C881/C881M(e) Linear shrinkage and thermal expansion according to

ASTM C531

8.4—ApplicationManufacturer’s recommendations should be carefully

followed for successful overlay and repair projects. Take notes during operations regarding materials, sequencing, and color treatments to guide consistency. Spray-applied materials should be mixed to a workable consistency for the equipment used. Some materials require multiple compo-nents, so mixing and staging of materials should be care-fully planned. To prevent splashing and facilitate mixing, it is good practice to add powdered materials to liquids for blending. Elevation differences of 1/8 in. (3 mm) or greater usually require troweling or otherwise tooling to yield a smooth transition between surfaces.

8.4.1 Consistency—As in any decorative concrete applica-tion, a consistent finish is essential. Decorative overlay and repair materials often require multiple batches to complete a project, which makes consistency in mixing and propor-tioning procedures a critical quality control issue. Some suppliers provide concrete dyes to offset slight color varia-tions. This procedure requires wet samples, the ability to differentiate subtle color variances, and attention to detail. Alternatively, light applications of differing colors can produce pleasing mottled affects that mask variation.

8.4.2 Saw markings—Although saw markings are gener-ally used for establishing crack locations, they can also be used for decorative affects. Saw markings can be filled with sealant or decorative sands, followed by impregnation with a polymer for a decorative affect.

8.4.3 Jointing—Joints are required, depending on the material used, span, underlayment condition, and repair application. Joint sealants and jointing procedures should be matched to the material(s) used and conform to manu-facturer’s recommendations. The width of all exposed joints in the final repair should be reasonably consistent, and the treatment procedures and materials used should produce a uniform appearance.

8.4.4 Curing—Polymer-modified cementitious overlays are self-curing in calm air, but should be protected from wind. Wind can cause intense plastic shrinkage cracking, so wind protection is an important consideration. Membrane-forming curing compounds are not required. Water curing






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with sprinkling and mats can distort the repair color. The overlay can be destroyed if watered when it is not fully set. The best solution to curing is to plan for wind protection and, when using two-coat systems, apply the finish coat as soon as the base coat is dry to the touch.

8.4.5 Sealing and waterproofing—The use of sealers with decorative overlay and repair materials is much the same as presented in 3.9. Sealer or waterproofing materials some-times contain solvents that negatively react with the poly-mers present in polymer-modified cementitious products. Material compatibility should be addressed in advance of the application of the sealer or waterproofing material. They should be resistant to ultraviolet (UV) light exposure and allow vapor transmission. Sealers should be UV-resistant when styrene-butadiene resin (SBR) is the polymer modifier because SBR is especially susceptible to ozone attack. Most waterproofing materials penetrate into material being sealed and do not alter the profile of the decorative overlay.

8.5—Touch-ups and post-repair aesthetic treatments

8.5.1 Touch up with chemical stains—Chemically stained surfaces that exhibit wear paths or areas where the concrete has been damaged or patched are difficult to re-stain success-fully. It is difficult to clean and apply stains to wear paths or small areas without overlapping it onto undamaged areas, causing unwanted discoloration. If design considerations allow, the entire area should be lightly abraded to remove or mask the damaged areas, then re-stained. The use of concrete dyes is effective for touch-up or repair of an acid-stained area that has been damaged.

8.5.2 Treatment of patches—Due to differences in chem-ical composition, patches will produce a different color than that of the surrounding concrete when chemically stained. The entire area can be renovated by use of a self-leveling cementitious topping after the underlying concrete is patched and the stain reapplied to the topping. Tests should be performed in advance to determine how well the topping will react with the chemical stain. Some topping materials react extremely well and others do not. Trowel-grade mate-rials such as microtoppings are also suitable for this type of resurfacing. The nature of the bond between the topping and patching materials is often different than the surrounding slab. The surface of repaired areas should be prepared in accordance with 8.1.4.

8.5.3 Surface topping repairs—Cracks or tears in topping materials should be filled or sealed in accordance with manufacturer’s recommendations. Mineral buildup or staining from ponding in low areas cause discoloration, so acceptable flatness tolerances should be specified via the FF or FL methods or other reasonable gauge. Use hand tools or textured mats to ensure the texture of a patch matches the surrounding surfaces. Misaligned templates, pattern lines, or both, are corrected with a small hand grinder with a tuck-point blade.

CHAPTER 9—MAINTENANCE

9.1—GeneralConcrete, like all materials, should be properly maintained

to reach its maximum service life. Maintenance require-ments vary, so designers should consult the manufacturer’s recommendations before specifying a specific decorative application. Special consideration should be given to the concrete’s exposure to the elements, service condition, and potential for wear to the concrete surface. Minimal use of deicers is recommended, as they can chemically attack deco-rative treatments and increase freezing-and-thawing cycles that can lead to surface damage.

Decorative concrete is durable and sustainable and will withstand abuse that many other building materials will not. In many instances, it is an art form and many projects are credited for using art as part of the design. With this in mind, maintenance is of the utmost importance. Cleaning and sealing decorative finishes will extend the service life of most decorative concrete finishes.

9.2—Coatings and sealersDepending on product formula and exposure to wear,

coatings and sealers will have different maintenance needs. Cleaning with mild soap and water is generally recom-mended; consult the sealer manufacturer for their specific cleaning recommendations. Carefully follow the manufac-turer’s recommendations for coating and sealer maintenance and a prescribed schedule. Sealed surfaces should be peri-odically recoated as the coating wears off the surface. Some interior surfaces should be maintained with a commercial-grade floor wax. Wax should be applied only after floors have been cleaned to avoid build-up of dirt and wax. Some materials require resealing or the application of salt-resistant coatings every 12 to 24 months. Commercial applications subject to high wear require more frequent maintenance.

9.3—Stained concreteChemically stained concrete flatwork should be main-

tained by periodic sweeping and washing with water using a standard garden hose. Areas of heavier soil are cleaned with a pH-neutral commercial detergent and wet-mopped or scrubbed with a stiff-bristle brush. Larger areas can be cleaned with a pressure washer or a walk-behind scrubbing machine. Care should be taken to ensure the washing process does not damage the concrete’s finish.

9.4—Color hardened and densified concreteHardened and densified concrete is very tough and, unlike

topically applied materials, should not require periodic recoating. As with any decorative treatment, it is important that manufacturer-recommended maintenance procedures and schedules are followed. No wax is required or recom-mended, but a neutral to medium high (9.5 or 10) pH cleaner containing a small amount of replenishment densifier formu-lated into the product is used to prevent loss of gloss and premature wear.






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9.5—Maintenance plan and closeout documentation

The installer should consult with the product manufac-turers when creating the maintenance plan for the final work. The plan should include recommended procedures, products, technical data sheets, and Material Safety Data Sheets for products recommended. The maintenance instruc-tions should be delivered with the document packet to the owner or owner’s representative. Include a statement on the job completion sign-off sheet acknowledging delivery and understanding of the maintenance requirements.

CHAPTER 10—REFERENCESAmerican Concrete InstituteACI 117-10—Specification for Tolerances for Concrete

Construction and Materials and CommentaryACI 301-10—Specifications for Structural ConcreteACI 302.1R-04—Guide for Concrete Floor and Slab

ConstructionACI 305R-10—Guide to Hot Weather ConcretingACI 308.1-11—Specification for Curing ConcreteACI 318-11—Building Code Requirements for Structural

Concrete and CommentaryACI 360R-10—Guide to Design of Slabs-on-GroundACI 544.5R-10—Report on the Physical Properties and

Durability of Fiber-Reinforced Concrete

ASTM InternationalASTM C33/C33M-11—Standard Specification for

Concrete AggregatesASTM C469/C469M-10—Standard Test Method for

Static Modulus of Elasticity and Poisson’s Ratio of Concrete in Compression

ASTM C531-00(2012)—Standard Test Method for Linear Shrinkage and Coefficient of Thermal Expansion of Chem-ical Resistant Mortars, Grouts, Monolithic Surfacings, and Polymer Concretes

ASTM C881/C881M-10—Standard Specification for Epoxy Resin Base Bonding Systems for Concrete

ASTM C979/C979M-10—Standard Specification for Pigments for Integrally Colored Concrete

ASTM C1090-10—Standard Test Method for Measuring Changes in Height of Cylindrical Specimens of Hydraulic Cement Grout

ASTM C1583/C1583M-13—Standard Test Method for Tensile Strength of Concrete Surfaces and the Bond Strength or Tensile Strength of Concrete Repair and Overlay Mate-rials by Direct tension (Pull of Method)

ASTM E1155-96(2008)—Standard Test Method for Determining FF Floor Flatness and FL Floor Levelness Numbers

ASTM F1869-11—Standard Test Method for Measuring Moisture Vapor Emission Rate of Concrete Subfloor Using Anhydrous Calcium Chloride

ASTM F2170-11—Standard Test Method for Deter-mining Relative Humidity in Concrete Floor Slabs Using In Situ Probes

Cited referencesASCC, 2003, “Hard Trowel Finish on Air-Entrained

Concrete,” Position Statement #1, American Society of Concrete Contractors, St. Louis, MO, 1 p.

Lerch, W., 1957, “Plastic Shrinkage,” ACI Journal, V. 53, No. 8, Aug., pp. 797-802.







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As ACI begins its second century of advancing concrete knowledge, its original chartered purpose remains “to provide a comradeship in finding the best ways to do concrete work of all kinds and in spreading knowledge.” In keeping with this purpose, ACI supports the following activities:

· Technical committees that produce consensus reports, guides, specifications, and codes.

· Spring and fall conventions to facilitate the work of its committees.

· Educational seminars that disseminate reliable information on concrete.

· Certification programs for personnel employed within the concrete industry.

· Student programs such as scholarships, internships, and competitions.

· Sponsoring and co-sponsoring international conferences and symposia.

· Formal coordination with several international concrete related societies.

· Periodicals: the ACI Structural Journal and the ACI Materials Journal, and Concrete International.

Benefits of membership include a subscription to Concrete International and to an ACI Journal. ACI members receive discounts of up to 40% on all ACI products and services, including documents, seminars and convention registration fees.

As a member of ACI, you join thousands of practitioners and professionals worldwide who share a commitment to maintain the highest industry standards for concrete technology, construction, and practices. In addition, ACI chapters provide opportunities for interaction of professionals and practitioners at a local level.

American Concrete Institute38800 Country Club DriveFarmington Hills, MI 48331U.S.A.Phone: 248-848-3700Fax: 248-848-3701

www.concrete.org






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The AMERICAN CONCRETE INSTITUTE

was founded in 1904 as a nonprofit membership organization dedicated to public service and representing the user interest in the field of concrete. ACI gathers and distributes information on the improvement of design, construction and maintenance of concrete products and structures. The work of ACI is conducted by individual ACI members and through volunteer committees composed of both members and non-members.

The committees, as well as ACI as a whole, operate under a consensus format, which assures all participants the right to have their views considered. Committee activities include the development of building codes and specifications; analysis of research and development results; presentation of construction and repair techniques; and education.

Individuals interested in the activities of ACI are encouraged to become a member. There are no educational or employment requirements. ACI’s membership is composed of engineers, architects, scientists, contractors, educators, and representatives from a variety of companies and organizations.

Members are encouraged to participate in committee activities that relate to their specific areas of interest. For more information, contact ACI.

www.concrete.org







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Guide to Decorative Concrete · hardscapes. Using color and texture introduced concrete as a landscape feature in addition to its functionality. An example is flatwork textured and

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