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SSPC-SP COMApril 1, 2000

SSPC: The Society for Protective Coatings

SURFACE PREPARATION SPECIFICATIONS

Surface Preparation Commentary for Steel and Concrete Substrates

1. Introduction

This Surface Preparation Commentary (SP COM) isintended to be an aid in selecting the proper surfacepreparation method, materials, and specification for steel,concrete, and other metallic substrates. A compilation ofstandards, guides, and specifications related to the surfacepreparation and coating of concrete is available as a sepa-rate publication from SSPC. The SP COM is not part of theactual specification, but is included to provide a betterunderstanding of the SSPC surface preparation specifica-tions. In addition, surface preparation specifications otherthan those published by SSPC are referenced.

The SSPC specifications, summarized in Table 1,represent a broad consensus of users, suppliers, andpublic interest groups. Details of the methods used tomeasure many of the properties in this SP COM are de-scribed in SSPC publication 97-07, The Inspection of Coat-ings and Linings, A Handbook of Basic Practice for Inspec-tors, Owners, and Specifiers.

2. Contents

1. Introduction2. Contents3. Importance of Surface Preparation4. Surface Conditions

4.1 New Construction4.2 Maintenance4.3 Surface Contaminants

4.3.1 Rust4.3.2 Mill Scale4.3.3 Grease and Oil4.3.4 Dirt and Dust4.3.5 Moisture4.3.6 Soluble Salts4.3.7 Paint Chalk4.3.8 Deteriorated Paint

4.4 Surface Defects4.4.1 Welds and Weld Spatter4.4.2 Weld Porosity4.4.3 Sharp Edges4.4.4 Pits4.4.5 Laminations, Slivers4.4.6 Crevices

4.5 Rust Back5. Summary of SSPC Surface Preparation Specifica-

tions5.1 SSPC-SP 1, "Solvent Cleaning"

5.1.1 Petroleum and Coal Tar Sol-vents, and Turpentine

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5.1.2 Alkaline Cleaners5.1.3 Emulsion Cleaners5.1.4 Steam Cleaning5.1.5 Threshold Limit Values5.1.6 Paint Removal

5.2 SSPC-SP 2, "Hand Tool Cleaning"5.2.1 Loose Rust, Mill Scale, and Paint5.2.2 Visual Standards

5.3 SSPC-SP 3, "Power Tool Cleaning"5.3.1 Loose Rust, Mill Scale, and Paint5.3.2 Visual Standards

5.4 SSPC-SP 4, "Flame Cleaning of NewSteel"

5.5 SSPC-SP 5/NACE No. 1, "White MetalBlast Cleaning"4.5.1 Visual Standards

5.6 SSPC-SP 6/NACE No. 3, "CommercialBlast Cleaning"4.6.1 Visual Standards

5.7 SSPC-SP 7/NACE No. 4, "Brush-Off BlastCleaning"4.7.1 Visual Standards

5.8 SSPC-SP 8, "Pickling"5.9 SSPC-SP 9, "Weathering Followed by

Blast Cleaning"5.10 SSPC-SP 10/NACE No. 2, "Near-White

Blast Cleaning"5.10.1 Visual Standards

5.11 SSPC-SP 11, "Power Tool Cleaning toBare Metal"5.11.1 Power Tools and Cleaning

Media5.11.2 Power Tools with Vacuum

Shrouds5.11.3 Visual Standards

5.12 SSPC-SP 12/NACE No. 5, “SurfacePreparation and Cleaning of Steel andOther Hard Materials by High- andUltrahigh-Pressure Water Jetting Prior toRecoating”5.12.1 Surface Cleanliness5.12.2 Flash Rusting5.12.3 Visual Standards

5.13 SSPC-SP 13/NACE No. 6, “SurfacePreparation of Concrete”

5.14 SSPC-SP 14/NACE No. 8, “IndustrialBlast Cleaning”5.14.1 Visual Standards

6. Selection of Abrasives, Blast Cleaning Param-eters, and Equipment6.1 Abrasive Characteristics

6.1.1 Hardness6.1.2 Size


6.1.3 Shape6.1.4 Bulk Density6.1.5 Friability/Waste Generation6.1.6 Recyclability

6.2 Factors Affecting Surface Profile6.3 Parameters That Affect Productivity

6.3.1 Particle Size6.3.2 Hardness6.3.3 Shape6.3.4 Specific Gravity6.3.5 Nozzle Pressure6.3.6 Nozzle Type6.3.7 Nozzle to Surface Distance6.3.8 Impact Angle6.3.9 Abrasive Metering6.3.10 Abrasive Cleanliness6.3.11 Embedment

6.4 Abrasive Types6.4.1 Metallic Abrasives6.4.2 Non-Metallic Abrasives

6.5 Blast Equipment6.5.1 Conventional Blasting6.5.2 Vacuum Blasting6.5.3 Abrasive Blast Cleaning Above

760 kPa (110 psi)7. Summary of SSPC Abrasive Specifications

7.1 SSPC-AB 1, "Mineral And Slag Abra-sives"

7.2 SSPC-AB 2, “Specification for Cleanlinessof Recycled Ferrous Metallic Abrasives”

7.3 SSPC-AB 3, “Newly Manufactured or Re-Manufactured Steel Abrasives”

8. Wet Abrasive Blast and Water Jetting Methods8.1 Water Cleaning and Water Jetting without

Abrasive8.1.1 Degrees of Cleaning8.1.2 Profile8.1.3 Water Consumption8.1.4 Equipment8.1.5 Flash Rust

8.2 Wet Abrasive Blast Cleaning8.2.1 Air/Water/Abrasive Blasting8.2.2 Water/Abrasive Blast Cleaning

8.3 Flash Rust and Inhibitors9. Other Cleaning Methods

9.1 Chemical Stripping9.2 Sodium Bicarbonate Blasting9.3 Sponge Jetting9.4 Carbon Dioxide (Dry Ice) Blasting9.5 Electrochemical Stripping

10. Film Thickness11. Visual Standards

11.1 SSPC-VIS 1-89,"Visual Standard ForAbrasive Blast Cleaned Steel"

11.2 SSPC-VIS 2, “Standard Method OfEvaluating Degree Of Rusting On PaintedSteel Surfaces”

11.3 SSPC-VIS 3, "Visual Standard For Power-and Hand-Tool Cleaned Steel"

11.4 SSPC-VIS 4/NACE No. 7, “Interim GuideAnd Visual Reference Photographs For

Steel Cleaned By Water Jetting”11.5 ISO Visual Standards11.6 Other Photographic Standards11.7 Project Prepared Standards

12. Other SSPC Surface Preparation Documents inthis Volume12.1 SSPC-TR 1/NACE 6G194, “Joint Tech-

nology Report on Thermal Precleaning”12.2 SSPC-TR 2/NACE 6G198, “Joint Techni-

cal Report on Wet Abrasive Blast Clean-ing”

12.3 SSPC-TU 2/NACE 6G197, “InformationalReport and Technology Update onDesign, Installation, and Maintenance ofCoating Systems for Concrete Used inSecondary Containment”

12.4 SSPC-TU 4, “Field Methods for Retrievaland Analysis of Soluble Salts on Sub-strates”

12.5 SSPC-TU 6, "Chemical Stripping ofOrganic Coatings from Steel Structures"

13. Non-SSPC Cleaning Specifications14. Surface Preparation of Concrete for Coating

14.1 Industry Standards14.2 Methods of Cleaning Concrete

3. Importance of Surface Preparation

Often, the surface preparation of steel for paintingrequires a three step process: 1) initial pre-cleaning toremove grease, oil, and dirt; 2) cleaning with hand/powertools, pressurized water, chemicals, or abrasive blasting; 3)creation or verification of the proper anchor pattern profile.The life of a coating depends as much on the degree ofsurface preparation as on the selected coating system,because most coating failures can be attributed to inad-equate surface preparation or lack of coating adhesion.Surface preparation, therefore, should receive thoroughconsideration. The primary functions of surface preparationare:

• To remove surface contaminants that can inducepremature coating failure.

• To provide a clean surface with adequate profile forgood coating adhesion.

Where abrasive blast cleaning is not allowed or isimpractical, alternative abrasives or methods of cleaningthe surface must be employed. Chemical stripping willremove paint and is relatively easy to contain. Hence,chemical stripping may be used around sensitive machin-ery or in densely populated areas. (Refer to SSPC-TU 6,“Chemical Stripping of Organic Coatings from Steel Struc-tures.”) Alternative abrasives such as sodium bicarbonate(baking soda) or dry ice (CO

2) can sometimes be used inplaces where conventional abrasives cannot be used. Aclass of abrasives has been developed where each abra-sive particle is contained in a urethane sponge. The sponge

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TABLE 1SUMMARY OF CURRENT SSPC ABRASIVE AND SURFACE PREPARATION SPECIFICATIONS

SSPC SPECIFICATION DESCRIPTIONAB 1Mineral and Slag Abrasives

AB 2Specification for Cleanliness ofRecycled Ferrous Metallic Abrasive

AB 3Newly Manufactured orRe-Manufactured Steel Abrasives

SP 1Solvent Cleaning

SP 2Hand Tool Cleaning

SP 3Power Tool Cleaning

SP 5/NACE No. 1White Metal Blast Cleaning

SP 6/NACE No. 3Commercial Blast Cleaning

SP 7/NACE No. 4Brush-Off Blast Cleaning

SP 8Pickling

SP 10/NACE No. 2Near-White Blast Cleaning

SP 11Power Tool Cleaning toBare Metal

SP 12/NACE No. 5Surface Preparation and Cleaningof Steel and Other Hard Materialsby High- and Ultrahigh-PressureWater Jetting Prior to Recoating

SP 13/NACE No. 6Surface Preparation of Concrete

SP 14/NACE No. 8Industrial Blast Cleaning

VIS 1-89Visual Standard for AbrasiveBlast Cleaned Steel

VIS 2Standard Method of EvaluatingDegree of Rusting on PaintedSteel Surfaces

VIS 3Visual Standard for Power- andHand-Tool Cleaned Steel

VIS 4/NACE No. 7Interim Guide and VisualReference Photographs for SteelCleaned by Water Jetting

Definition of requirements for selecting and evaluating mineral and slag abrasive used for blast cleaning.

Cleanliness requirements for a recycled work mix and a description of the test procedures.

Requirements of chemical and physical properties of steel abrasives.

Removal of oil, grease, dirt, soil, salts, and contaminants by cleaning with solvent, vapor, alkali, emulsion,or steam.

Removal of loose rust, loose mill scale, and loose paint to degree specified, by hand chipping, scraping,sanding, and wire brushing.

Removal of loose rust, loose mill scale, and loose paint to degree specified, by power tool chipping, descaling,sanding, wire brushing, and grinding.

Removal of all visible rust, mill scale, paint, and foreign matter by blast cleaning by wheel or nozzle (dry orwet) using sand, grit or shot. For very corrosive atmospheres where high cost of cleaning is warranted.

Blast cleaning until at least two-thirds of the surface is free of all visible residues with only staining permittedon the remainder. For conditions where a thoroughly cleaned surface is required.

Blast cleaning of all except tightly adhering residues of mill scale, rust, and coatings, while uniformlyroughening the surface.

Complete removal of rust and mill scale by acid pickling, duplex pickling, or electrolytic pickling.

Blast cleaning nearly to White Metal cleanliness, until at least 95% of the surface is free of all visible residueswith only staining permitted on the remainder. For high humidity, chemical atmosphere, marine, or othercorrosive environments.

Complete removal of all rust, scale, and paint by power tools, with resultant surface profile.

Defines four degrees of cleaning for visible contaminants (similar to SP 5, 6, 7, and 10) and three levels ofsurface cleanliness for non-visible soluble salt contamination.

Description of inspection procedures prior to surface preparation, methods of surface preparation, inspection,and classification of prepared concrete surfaces.

Between SP 7 (brush-off) and SP 6 (commercial). The intent is to remove as much coating as possible, butcontaminants difficult to remove can remain on 10 percent of the surface.

Standard reference photographs; recommended supplement to SSPC Surface Preparation SpecificationsSSPC-SP 5, 6, 7, and 10.

A geometric numerical scale for evaluating degree of rusting of painted steel. Color photographs showstaining while matching black and white images depict only rust. Three rust distributions, general, spot, andpinpoint, are depicted.

Standard reference photographs; recommended supplement to SSPC-SP 2, 3, and 11.

Standard reference photographs depict previously rusted steel cleaned by water jetting. Photographs depictthree levels of flash rusting. Recommended as a supplement to SSPC-SP 12.

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contains the abrasive and facilitates cleanup and recycling.An advantage of all wet blast methods is the control of

dust emissions. Wet blast methods may involve wateralone, abrasive injected into the water stream, water in-jected into an abrasive air stream, or a water curtainsurrounding an air/abrasive stream. Power tools with vacuumshrouds have also been proven effective in controlling dustemissions, particularly in removing lead containing paint. Inapplications where the presence of soluble salts on thesteel surface creates a serious problem, such as tanklinings, it may be beneficial to incorporate water into thecleaning process.

To gain maximum benefit from a high performanceindustrial coating, it is not prudent to cut back on the surfacepreparation. Surface preparation is important even when a“surface tolerant” coating is used. When the manufacturerclaims a particular coating will “tolerate” a given amount ofrust, old paint, or other contamination on the steel surface,it is likely that the coating will perform even better if thesurface is prepared to a higher level of cleanliness.

4. Surface Conditions

The initial condition of the surface to be cleaned willdetermine the amount of work, time, and money required toachieve any particular degree of surface cleanliness. It ismore difficult to remove contaminants from rusty steel thanfrom intact mill scale. Therefore, it is necessary to considerthe surface condition prior to selecting the method ofcleaning.

The initial condition of the steel may determine thechoice of abrasive to be used. Steel shot is an economicaland effective choice for removing intact mill scale. How-ever, if the steel is rusted and/or pitted, a more angularabrasive such as steel grit or a nonmetallic mineral abrasivewill more effectively “scour out” the rust.

Although there are almost an infinite number of initialconditions, they can be broadly categorized as follows:

• New construction—steel not previously painted• Maintenance—previously painted steel• Surface contaminants—common to both new

construction and maintenance

4.1 NEW CONSTRUCTION: For new construction thereare four surface conditions based upon the rust gradeclassifications of SSPC-VIS 1-89, “Visual Standard forAbrasive Blast Cleaned Steel” as follows:

Rust Grade A - Steel surface covered completelywith adherent mill scale; little or no rust visibleRust Grade B - Steel surface covered with both millscale and rustRust Grade C -Steel surface completely covered withrust; little or no pitting visible

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Rust Grade D -Steel surface completely covered withrust; pitting visible

4.2 MAINTENANCE: The pictorial standard SSPC-VIS3, “Visual Standard for Power- and Hand-Tool CleanedSteel,” defines conditions E, F and G for previously paintedsurfaces.

Condition E - Light-colored paint applied over ablast-cleaned surface, paint mostly intact.Condition F - Zinc-rich paint applied over blast-cleaned steel, paint mostly intact.Condition G - Painting system applied over mill scalebearing steel; system thoroughly weathered, thor-oughly blistered, or thoroughly stained.

In maintenance repainting, the degree of surface prepa-ration required depends on the new painting system and onthe extent of degradation of the surface to be painted. Theamount of rusting on a surface is based on the numericalscale of 0 to 10 given in SSPC-VIS 2 (ASTM D 610),“Standard Method of Evaluating Degree of Rusting onPainted Steel Surfaces,” where a rating of 10 indicates norust and a rating of 0 indicates totally rusted. SSPC-PAGuide 4, “Guide to Maintenance Repainting with Oil Base orAlkyd Painting Systems,” suggests the minimum surfacepreparation needed for each degree of rusting. The SSPCPainting System Commentary will also help in estimatingsurface preparation requirements.

In estimating rust percentages, photographs and sche-matic diagrams of the type shown in SSPC-VIS 2 can serveas practical aids. The Guide to SSPC-VIS 2, published inthis volume, shows black and white schematics of actualrust patterns which serve as guides for judging the percent-age of surface covered by rust (after removal of stains) orrust blisters. The present edition of SSPC-VIS 2 showsthree different configurations of rusting – general, pinpoint,and spot rust, rather than the single configuration that wasavailable prior to 2000.

Comments on surface preparation for maintenancerepainting are given in SSPC-PA Guide 4, “Guide to Main-tenance Repainting with Oil Base or Alkyd Painting Sys-tems.” This guide includes a description of accepted prac-tices for retaining old, sound paint, removing unsoundpaint, feathering, and spot cleaning.

4.3 SURFACE CONTAMINANTS: Typical contami-nants that should be removed during surface preparationare rust, corrosion products, mill scale, grease, oil, dirt,dust, moisture, chloride salts, sulfate salts, paint chalk, andloose, cracked, or peeling paint.

4.3.1 Rust: Rust consists primarily of iron oxides, thecorrosion products of steel. Whether loose or relativelytightly adherent, rust must be removed for satisfactorycoating performance. Rust resulting from the corrosion of

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steel is not a good base for applying coatings because itexpands and becomes porous. So-called “over-rust prim-ers” (also referred to as “rust converters”) do not perform aswell as conventional coatings applied over clean steel, andthe effectiveness of rust converters is unproven.

4.3.2 Mill Scale: Mill scale is a bluish, somewhat shinyoxide residue that forms on steel surfaces during hot rolling.Although initially tightly adhering, it eventually cracks, pops,and disbonds. As a general rule, unless completely re-moved before painting, it will later cause the coatings tocrack and expose the underlying steel. Steel is anodic tomill scale and so corrodes more rapidly in this combinationof “dissimilar metals.”

Mill scale is erratic in its effect upon the performance ofcoatings. Tightly adhered or intact mill scale may not haveto be removed for mild atmospheric exposure. If, however,the steel surface is to be coated with primers with lowwetting properties or exposed to severe environments suchas chemical exposures or immersion in fresh or salt water,then removal of mill scale by blast cleaning to a minimumSSPC-SP 6, “Commercial Blast Cleaning,” is necessary.

4.3.3 Grease and Oil: Even thin films of grease and oil,which may not be readily visible, can prevent tight bondingof coatings. Visible deposits of grease and oil should beremoved by solvent cleaning, SSPC-SP 1, prior to abrasiveblast cleaning. If this precleaning is not done, the abrasiveblasting may spread the grease or oil over the surfacewithout removing it.

4.3.4 Dirt and Dust: Dirt and dust can also preventtight bonding of coatings, and should be removed com-pletely.

4.3.5 Moisture: Steel surfaces must be dry beforeblast cleaning and painting. Moisture may either produceflash rusting before painting or accelerate underfilm corro-sion after painting. Water can also prevent an organiccoating from properly “wetting out” the surface on metal orconcrete surfaces, and may disrupt the curing of the coating.

4.3.6 Soluble Salts: Soluble salts are deposited fromthe atmosphere onto surfaces. If they remain on the surfaceafter cleaning, they can attract moisture which can perme-ate the coating and cause a blister (osmotic blistering).Salts, particularly chlorides, may also accelerate the corro-sion reaction and underfilm corrosion. Methods for measur-ing the amount of salt on the surface are described inSSPC-TU 4, “Field Methods for Retrieval and Analysis ofSoluble Salts on Substrates.” In some circumstances it isdesirable to remove soluble salts by power washing or othermethod prior to abrasive blast cleaning.

4.3.7 Paint Chalk: The sun’s ultraviolet light causes allexterior organic coatings to chalk to some extent. Chalk is

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the residue left after deterioration of the coating’s surfaceorganic binder. All loose chalk must be removed beforecoating in order to avoid intercoat adhesion problems. It isoften specified that, before topcoating, old paint must havea rating of no less than 8 in accordance with ASTM D 4214,“Test Method for Evaluating Degree of Chalking of ExteriorPaint Films.”

4.3.8 Deteriorated Paint: All loose paint must beremoved before maintenance painting. Before removingany old paint, it must be determined whether the paintcontains significant amounts of lead or other toxic material.If so, then special precautions must be taken to protectworkers, others in the area, and the environment.

4.4 SURFACE DEFECTS: Coatings tend to draw thinand pull away from sharp edges and projections, leavinglittle or no coating to protect the underlying steel, therebyincreasing the potential for coating failure. Other featureswhich are difficult to properly cover and protect includecrevices, weld porosity and laminations discussed below.The high cost to remedy these surface imperfections re-quires weighing the benefits of edge rounding or grinding,versus a potential coating failure.

Poorly adhering contaminants, such as weld slag resi-dues, loose weld spatter, and some minor surface lamina-tions, may be removed by abrasive blast cleaning. Othersurface defects, such as steel laminations, weld porosities,or deep corrosion pits, may not be evident until afterabrasive blast cleaning. Therefore, the timing of such sur-face repair work may occur before, during, or after prelimi-nary surface preparation operations have begun.

4.4.1 Welds and Weld Spatter: Weld spatter shouldbe removed prior to blast cleaning. Most weld spatter,except that which is very tightly adherent, can be readilyremoved using a chipping hammer, spud bar, or scraper.Tightly adhering weld spatter may require removal by grind-ing. Weld spatter that is not removed will have a low filmthickness (as on sharp edges) and can disbond from thebase metal, resulting in adhesion failure. Welds can alsohave sharp projections that may stick out of the wet paint.The details on grinding welds are discussed in NACERP0178, “Standard Recommended Practice, FabricationDetails, Surface Finish Requirements, and Proper DesignConsiderations for Tanks and Vessels to Be Lined forImmersion Service.”

4.4.2 Weld Porosity: Areas of unacceptable porosityas defined in the American Welding Society standard AWSD1.1 should be investigated and, if needed, filled withacceptable filler material or closed over with a needle gunor peening hammer prior to painting. Acceptable weldprofiles, arc strikes, and weld cleaning are also addressedin Section 3 of AWS D1.1, “Structural Welding Code.”


4.4.3 Sharp Edges: Sharp edges, such as those nor-mally occurring on rolled structural members or plates, aswell as those resulting from flame cutting, welding, grind-ing, etc., and especially shearing, could have an influenceon coating performance and may need to be removed (e.g.,grinding, mechanical sanding, filing). Care should be takento ensure that during the removal operations, new sharpedges are not created.

4.4.4 Pits: Deep corrosion pits, gouges, clamp marks,or other surface discontinuities may require grinding prior topainting. The surface may also require filling with weldmaterial.

4.4.5 Laminations, Slivers: Rolling discontinuities(laps) may have sharp protruding edges and deep penetrat-ing crevices and such defects should be eliminated prior topainting. Various methods can be used to eliminate minorslivers (e.g., scraping and grinding). All sharp fins, projec-tions, or edges should be removed. Filing may also benecessary.

4.4.6 Crevices: Areas of poor design for corrosionprotection, such as tack or spot welded connections, back-to-back angles, crevices, etc., may require special atten-tion. Where possible, such deficiencies should be correctedby structural or design modification. Where this is notpossible, filling, and/or special surface preparation andpainting procedures may be needed.

4.5 RUST BACK: Rust back occurs when freshly ex-posed bare steel is exposed to conditions of high humidity,moisture, or a corrosive atmosphere. The time intervalbetween blast cleaning and rust back will vary greatly (fromminutes to weeks) from one environment to another. Be-cause of this factor, timeliness of inspection is of greatimportance. Inspection must be coordinated with thecontractor’s schedule of operation in such a way as to avoiddelay. Acceptance of the prepared surface must be madeprior to application of the prime coat, because the degree ofsurface preparation cannot be readily verified after paint-ing.

Under normal mild atmospheric conditions it is best tocoat a blast cleaned surface within 24 hours after blastcleaning. Under no circumstances should the steel bepermitted to rust back before painting, regardless of thetime elapsed. If visible rust occurs prior to painting, sur-faces must be re-cleaned to meet contract cleaning require-ments (e.g. SSPC-SP 10/NACE No. 2). If immediate re-painting is desired by the contractor but the job has norequirements for independent inspection to accept thequality of the cleaned surface, it is incumbent upon thecontractor to verify, using recognized quality control tests,and document the quality of the cleaned surface beforeproceeding with application of the primer.

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Moisture condenses on any surface that is colder thanthe dew point of the surrounding air. It is therefore recom-mended that dry blast cleaning should not be conductedwhen the steel surface is less than 3 °C (5 °F) above thedew point.

Excessive weathering or exposure of steel to chemicalfumes such as chlorides and sulfates prior to blast cleaningshould be avoided since pitting of the steel may increasecleaning costs and makes removal of contaminants diffi-cult. After blast cleaning, even slight residues of chlorides,sulfates, or other electrolytes on the steel surface may beharmful and, for some coatings, may cause prematurecoating failure. If rust back is due to chemical contaminationof the surface, the contaminant should be removed prior tocoating, rather than coating the surface before rust backoccurs.

5. Summary of SSPC Surface PreparationSpecifications

Although these specifications are primarily intendedfor heavy metal or plate, most are also suitable for lightweight or thin section metal. Obviously, caution must beexercised when using methods such as abrasive blastcleaning on thin gage metal since damage by warping fromexcessive peening of the surface may occur. Occasions willarise where these specifications will not result in the type ofcleaning desired. In such cases, the contract documentsmay need to modify the surface preparation specificationsto obtain the result desired. Regardless of which methodsare used, adjacent equipment, pre-finished items, or sur-faces that could be damaged from the method of surfacepreparation must be protected.

Occasionally in maintenance painting the previouspaint is incompatible with the new paint. Under thesecircumstances all paint, regardless of condition, will have tobe removed. A minimum of SSPC-SP 6, “Commercial BlastCleaning” is usually necessary.

Volume 1 of the SSPC Painting Manual devotes sev-eral chapters to mechanical surface preparation, and it alsodiscusses special surface preparation requirements forshops, maintenance, railroads, highways, tanks, vessels,refineries, and various types of plants. This volume shouldbe consulted when choosing a surface preparation specifi-cation.

The “Commentary on Paint Specifications” shows theminimum surface preparation required for each of theSSPC specification paints. Similarly, the “Commentary onPainting Systems” shows the recommended minimum sur-face preparation for each paint system and for the variousindividual alternative primers within each system, in tencommon types of exposure.

The SSPC surface preparation specifications werenumbered according to the chronological order in whichthey were adopted, not according to their degree of thor-

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oughness of cleaning. For example, some time after SSPC-SP 5 (white metal) and SSPC-SP 6 (commercial) wereissued, a need arose for a standard between these two.Hence, the standard for Near-White Blast Cleaning wasdeveloped, but the next available number was SSPC-SP10. Similarly, SSPC-SP 14, “Industrial Blast Cleaning,” is adegree of cleaning between SSPC-SP 7 (brush-off) andSSPC-SP 6 (commercial).

5.1 SSPC-SP 1, “SOLVENT CLEANING”: This sol-vent cleaning specification includes simple organic solventwiping, immersion in solvent, solvent spray, vapordegreasing, alkaline cleaning, emulsion cleaning, and steamcleaning.

Solvent cleaning is used primarily to remove oil, grease,dirt, soil, drawing compounds, and other similar organiccompounds. Inorganic compounds such as chlorides, sul-fates, weld flux, rust, and mill scale are not removed bycleaning with organic solvents.

Many solvents are hazardous. Care must be takenwhen using solvents for solvent cleaning. Special safetyprecautions must be followed with regard to ventilation,smoking, static electricity, respirators, eye protection, andskin contact.

Detergent/water cleaning is a very gentle method ofsolvent cleaning. Aqueous solutions of household deter-gents may be effective in the removal of light deposits ofgrease and oil. They seldom have adverse effects onsubstrates.

Alkaline cleaning compounds cover a wide range incomposition and method of use. It is important that residuesof alkaline compounds do not remain on the surface aftercleaning. The cleaned surface may be tested with litmuspaper or universal indicating paper to see that it is neutralor at least no more alkaline than the rinse water that is used.Various solvent, alkaline, and detergent cleaning com-pounds are discussed in Volume 1 of the SSPC PaintingManual.

5.1.1 Petroleum and Coal Tar Solvents, and Turpen-tine: These types of solvents clean the metal by dissolvingand diluting the oil and greases which contaminate thesurface. All solvents are potentially hazardous and theyshould be used under such conditions that their concentra-tion in air being breathed by workmen is low enough forsafety (see Table 2). When used in closed spaces wherethe safe concentration is exceeded, fresh air masks shouldbe worn. The fresh air intake should be clear of carbonmonoxide or other contaminants from engine exhausts orother sources. The concentration of solvent in air should notexceed the lower limit of flammability as fire or explosionmay result. Some solvents, especially coal tar solvents(aromatics), will also dissolve the vehicle of paints so theycan be removed. It is important that the last wash or rinsebe made with clean solvent in every case or a film of oil orgrease will be left on the surface when the solvent of the last

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washing evaporates. This film may interfere with the bondof the paint to the metal.

Petroleum base mineral spirits (aliphatics), with a mini-mum flash point of 38°C (100°F) should be used as thegeneral purpose solvent for cleaning under normal condi-tions. In hot weather, or when the temperature is 25 to 35°C(80 to 95°F), high flash aliphatic mineral spirits with aminimum flash point of 50°C (122°F) should be used. Invery hot weather, when the temperature is over 35°C(95°F), heavy mineral spirits with a flash point over 60°C(140°F) should be used. Gasoline and V.M. & P. Naphthaare too dangerous for use under ordinary conditions.

Aromatic or coal tar solvents may be used wheregreater solvency is required, but they are more toxic and thesolvents generally available have low flash points. Benzol(benzene) is the most toxic and should not be used, particu-larly in view of its low flash point and attendant fire andexplosion hazard. Xylol, toluol, and high flash naphtha maybe used when their concentration in air that is being breatheddoes not exceed the safe limit (see Table 2). If the concen-tration is greater, fresh air masks should be worn. Becauseof the low flash points of these solvents, fire and explosionhazards are inherent with their use and great cautionshould be taken to ensure safe working conditions.

Chlorinated hydrocarbons may be used. However, dueto toxicity, chlorinated hydrocarbons are not recommendedfor general use except with special equipment and trainedoperators. Chlorinated hydrocarbons should never be usedwhere they may affect stainless steel.

“Safety solvents” are satisfactory for use provided thatthey meet the flash point requirements above and that theyare used under such conditions that the concentration ofchlorinated hydrocarbons in air does not constitute a healthhazard (see Table 2).

5.1.2 Alkaline Cleaners: These cleaners saponifycertain oils and greases, and their surface active constitu-ents wash away other types of contaminants, such as oil.They may be particularly effective in removing paint be-cause the alkali saponifies the dried paint vehicle. Since thesoaps formed are soluble in water, the contaminants aremore easily removed by washing with water after saponifi-cation. Although alkaline cleaners pose no problems to asteel substrate, they may cause significant damage toaluminum, zinc, wood, or concrete.

The most commonly used alkaline cleaner is trisodiumphosphate, but there are other alkalies which are used.Some of these are mixtures with wetting agents and deter-gents. They are available as proprietary products andshould be used in accordance with directions of the manu-facturer.

Because of the paint removal action of many alkalinecleaners, the actual cleaner to be used should be chosenafter consideration of the extent to which the paint may bedamaged.

If no manufactured alkaline cleaner is available, goodresults may be achieved by the use of 15 grams of trisodium


TABLE 2 THRESHOLD LIMIT VALUES (TLV) FOR SOLVENTS4

TLV-TWA1 TLV-STEL2

Substance ppm mg/m3 ppm mg/m3

Acetone 500 1780 750 2375Benzene (Benzol)—Skin 0.5 30 2.5 75Butylcellosolve—Skin 25 120 75 360Carbon Tetrachloride—Skin 5 30 10 125Cyclohexane 300 1050 — 1300Epichlorohydrin—Skin 0.5 10 — 20Ethyl Acetate 400 1400 — —Ethanol (Ethyl Alcohol) 1000 1900 — —Ethylene Dichloride (1, 2-Dichloroethane) 10 40 — 60Ethylenediamine 10 25 — —Furfuryl Alcohol—Skin 10 40 15 60Methanol (Methyl Alcohol)—Skin 200 260 250 310Methylene Chloride (Dichloromethane) 50 350 100 1740Naphtha, Coal Tar3 — — — —Naphtha, Petroleum3 — — — —Perchloroethylene—Skin 50 335 200 1340Isopropyl Alcohol—Skin 400 980 500 1225Stoddard Solvent 100 525 — 1050Toluene 50 375 — 560Trichloroethylene 50 270 100 1080Turpentine 100 560 — 840Xylene (Xylol) 100 435 150 655

[1] TLV-TWA (Threshold Limit Value—Time Weighted Average): The time-weighted average concentration for a conventional8-hour workday and a 40-hour workweek, to which it is believed that nearly all workers may be repeatedly exposed, day afterday, without adverse effect.[2] TLV-STEL (Threshold Limit Value—Short Term Exposure Limit): The maximum concentration to which workers can beexposed for a short time without suffering from irritation, chronic or irreversible tissue damage, or narcosis of sufficient degreeto increase the likelihood of accidental injury, impair self-rescue or materially reduce work efficiency, and provided that thedaily TLV-TWA is not exceeded. Exposures above the TLV-TWA up to STEL should not be longer than 15 minutes and shouldnot occur more than four times per day. There should be at least 60 minutes between successive exposures in this range.[3] In general, the aromatic hydrocarbon content will determine what TLV applies.[4] Reprinted from the American Conference of Governmental Industrial Hygienists booklet entitled “Threshold Limi t Values forChemical Substances and Physical Agents, Biological Exposure Indices” 1999 edition. These TLVs are revised annually. Notethat OSHA limits may be different (sometimes lower). Therefore, ACGIH recommendations can sometimes be illegal.

phosphate per liter of water (2 oz/gal), to which is alsoadded soap or other suitable detergent at 8 to 15 grams perliter (one to two ounces per gallon). This solution is bestused hot; if used cold, it may be advisable to increase theconcentration. This solution is suitable for spraying orscrubbing; if used in dip tanks, the concentration may betripled. If not washed from the surface, this mixture willsoften and eventually loosen most paints.

A soap film left on the surface is just as damaging to thepaint bond as is an oil or grease film; therefore the surfaceshould be thoroughly washed (preferably with hot waterunder pressure) to remove this soap and other residue.Moreover, all alkali must be thoroughly removed from thesurface or the new paint may be saponified and damagedby it. To test the effectiveness of the wash, universal pH testpaper should be placed against the wet steel. The pH of thewashed surface should be no greater than the pH of thewash water.

1

Alkaline cleaners must be used with caution since badburns may result from contact with some solutions. Particu-lar care should be paid to protecting the eyes of workers;safety goggles or eye shields should be worn. Rubbergloves should be worn if the solutions will contact workers’hands. Where alkaline cleaning compounds are sprayed,respirators should be worn.

5.1.3 Emulsion Cleaners: Emulsion cleaners usuallycontain oil soluble soaps or emulsifying agents along withkerosene or mineral spirits. They are usually supplied as aconcentrate which may be thinned with kerosene or mineralspirits and sprayed on the surface to be cleaned. They areemulsified by the action of water under pressure and washedaway along with oil, grease, and other contaminants. Theymay be diluted with water, emulsified, and used in thatcondition. In any event, the directions of the manufacturer

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should be followed.A residue of emulsion is almost always left on the

surface. This residue will leave a thin film of oil on thesurface. If the paint to be applied cannot tolerate a slightamount of oil, the residue must be washed from the surfaceby steam, hot water, detergents, solvents, or alkaline clean-ing compounds.

Alkaline emulsion cleaners, which combine the advan-tages of the alkaline cleaners and the emulsion cleaners,are available.

5.1.4 Steam Cleaning: Steam cleaning may utilizeeither steam, hot water under pressure, or both.

The steam and hot water, when used to clean thesurface, are usually used with a detergent and sometimesalso with an alkaline cleaner. The steam and hot waterthemselves tend to remove the oils, greases, and soaps bythinning them with heat, emulsifying them, and dilutingthem with water. It can then be easily removed by furtherwashing. When detergent is used, its higher affinity for themetal also causes the oil, grease and, in some cases, eventhe paint to loosen, thereby increasing the rate of cleaning.

The new paint will not adhere to the metal if any of theoil, grease, soap, detergent, or alkali is left on the surface.A final washing with clean water is therefore always neces-sary.

5.1.5 Threshold Limit Values: For threshold limitvalues of common cleaning solvents see the AmericanConference of Governmental Industrial Hygienists(ACHGIH) booklet entitled “1999 TLVs and BEIs, ThresholdLimit Values for Chemical Substances and Physical Agents,Biological Exposure Indices” (see Table 2).

5.1.6 Paint Removal: Although not addressed in SSPC-SP 1, many of the methods used to clean the surface mayactually remove paint. A strong solvent used in solventcleaning may cause old paint to disbond. The adhesivenature of the old paint is reduced by chemical action on thepaint. Where complete paint removal is the primary object,caustic soda (sodium hydroxide) or a commercial paintstripper may be used. Steam can be used to remove oldpaint by cooking the vehicle of the old paint so that it losesits strength and its bonding to the metal. Information onchemical stripping can be found in the technology updateSSPC-TU 6, “Chemical Stripping of Organic Coatings fromSteel Structures.”

5.2 SSPC-SP 2, “HAND TOOL CLEANING”: Handtool cleaning is a method of surface preparation often usedfor normal atmospheric exposures, for interiors, and formaintenance painting when using paints with good wettingability. Hand cleaning will remove loose rust, loose paint,and loose mill scale but will not remove all residue of rust orintact mill scale. For cleaning small, limited areas prior tomaintenance priming, hand cleaning will usually suffice.

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It is important to follow the good practices outlined inthis hand tool cleaning specification in order to minimizefailures or to avoid unnecessarily stringent specificationsfor the preparation of surfaces which will be exposed in mildenvironments. Care in hand tool cleaning is also especiallyimportant if the prime coat is to be applied by spray,because a sprayed coating may bridge gaps and crevices,whereas brushing works the paint into these areas.

The hand tool cleaning specification requires that oiland grease, along with any salts, be removed as specifiedin SSPC-SP 1, “Solvent Cleaning” prior to hand tool clean-ing. On welded work, particular care should be taken toremove as much welding flux, slag, and fume deposit as ispossible since these are notorious in promoting paint failureon welded joints. All loose matter should be removed fromthe surface prior to painting. Blowing it off with clean, dry,oil-free compressed air, brushing, or vacuum cleaning aresatisfactory methods.

5.2.1 Loose Rust, Mill Scale, and Paint: Determina-tion of the degree of cleaning required to comply withSSPC-SP 2 is often very difficult. The problem is in estab-lishing whether a residue is “adherent” or “loose.” Thespecification considers the residue adherent if it cannot belifted with a dull putty knife, a somewhat subjective criterion.

One definition of a dull putty knife is: "A dull putty knife isdefined as a commercially available putty knife consisting of aflexible metal blade solidly affixed to a handle. The width of theblade at the point of contact with the surface shall be 1 to 1.5inches. The edge of the blade at the point of contact shall bein the 'as purchased' condition, and shall not be altered bygrinding, sanding, or any other means that would affect thecontour of the edge. The putty knife shall not be used if the edgeis nicked or gouged, or if dry paint or other material is presentalong the edge that would prevent the blade from makingintimate contact with the surface. A blade containing surfacescratches from previous use is acceptable. The putty knifeshall be used at an approximately 45 degree angle to thesurface or lower in an attempt to work it under the edge ofmaterial being tested. The width of the blade, not either of thecorners, shall be used for the testing."

Another possible solution to determining what exactlyconstitutes "loose paint" is to establish a standard of clean-ing through use of a specified cleaning procedure in whichthe type of tool, force, speed, etc., are stipulated. Thesurface for the standard (or the control) should be a flatportion of the surface actually to be cleaned.

It is emphasized that this establishes a standard ofcleanliness, but not a production rate. As long as thesurface is cleaned as well as that in the standard cleaning,the actual production rate is not in question. The standardis of value in resolving differences of opinion as to whetheror not the surface has been properly cleaned.

5.2.2 Visual Standards: If mutually agreed upon,SSPC-VIS 3, ISO 8501-1, or other visual references may beused to supplement the cleaning criteria of this specifica-


TABLE 3Comparison of SSPC and ISO Surface Preparation Standards

Surface Preparation Standard Initial Condition of Steel Pictorial StandardSSPC/NACE ISO SSPC/ISO Descript ion SSPC-VIS 1 ISO 8501-1

SP 5/NACE No. 1White Metal Blast Cleaning

Sa 3 Rust Grade A intact millscale A SP-5, A SP 5-N1, A SP 5-N2,A SP 5-N3, A SP 5-M1, A SP 5-M2A SP 5-M3 (#)

A Sa 3**

Rust Grade B partially rusted millscale B SP-5 B Sa 3**Rust Grade C 100% rusted, no pits C SP-5 C Sa 3**Rust Grade D rusted and pitted D SP-5 D Sa 3

SP 10/NACE No. 2 Sa 2 1/2 Rust Grade A intact millscale A SP-10 A Sa 2 1/2Near White Blast Cleaning Rust Grade B partially rusted millscale B SP-10 B Sa 2 1/2

Rust Grade C 100% rusted, no pits C SP-10 C Sa 2 1/2Rust Grade D rusted and pitted D SP-10 D Sa 2 1/2

SP 6/NACE No. 3 Sa 2 Rust Grade A intact millscale * *Commercial Blast Cleaning Rust Grade B partially rusted millscale B SP-6 B Sa 2**

Rust Grade C 100% rusted, no pits C SP-6 C Sa 2Rust Grade D rusted and pitted D SP-6 D Sa 2

SP 7/NACE No. 4 Sa 1 Rust Grade A intact millscale * *Brush-Off Blast Cleaning Rust Grade B partially rusted millscale B SP-7 B Sa 1

Rust Grade C 100% rusted, no pits C SP-7 C Sa 1Rust Grade D rusted and pitted D SP-7 D Sa 1

SP 14/NACE No. 8 N/A Rust Grade A intact millscale *Industrial Blast Cleaning Rust Grade B partially rusted millscale * B Sa 2**

Rust Grade C 100% rusted, no pits *Rust Grade D rusted and pitted *

SSPC ISO SSPC SSPC-VIS 3 ISO 8501-1SP 2 St 2 Rust Grade A intact millscale A SP2 *Hand Tool Cleaning Rust Grade B partially rusted millscale B SP2 B St 2

Rust Grade C 100% rusted, no pits C SP2 C St 2Rust Grade D rusted and pitted D SP2 D St 2Condition E paint mostly intact E SP2 *Condition F zinc-rich paint F SP2 *Condition G deteriorated paint over millscale G SP2 *

SP 3 St 3 Rust Grade A intact millscale A SP3/PWB, A SP3/SD, A SP3/NG *Power Tool Cleaning Rust Grade B partially rusted millscale B SP3/PWB, B SP3/SD, B SP3/NG B St 3

Rust Grade C 100% rusted, no pits C SP3/PWB, C SP3/SD, C SP3/NG C St 3Rust Grade D rusted and pitted D SP3/PWB, D SP3/SD, D SP3/NG D St 3Condition E paint mostly intact E SP3/PWB, E SP3/SD, E SP3/NG *Condition F zinc-rich paint F SP3/PWB, F SP3/SD, F SP3/NG *Condition G deteriorated paint over millscale G SP3/PWB, G SP3/SD, G SP3/NG *

SP 11 Rust Grade A intact millscale A SP11 *Power Tool Cleaning to Bare Metal Rust Grade B partially rusted millscale B SP11 *

Rust Grade C 100% rusted, no pits C SP11 *Rust Grade D rusted and pitted D SP11 *Condition E paint mostly intact E SP11, E SP11/R *Condition F zinc-rich paint F SP11, F SP11/R *Condition G deteriorated paint over millscale G SP11 *

SSPC-VIS 1 contains photographs for SP 5, SP 6, SP 7 and SP 10. * = no photographSSPC-VIS 3 contains photographs for SP 2, SP 3 and SP 11.# Alternate non-metallic abrasives: A SP 5-N1, A SP 5-N2, A SP 5-N3# Alternate metallic abrasives: A SP 5-M1, A SP 5-M2, A SP 5-M3ISO standards Sa 3, Sa 2 1/2, Sa 2, Sa 1, St 2 and St 3 approximate the corresponding SSPC standards.**ISO 8501-1 photographs (1978 through 1989 printing) may not adequately illustrate the corresponding SSPC surface preparation.ISO photograph illustrating B Sa 2 shows dark areas that could be interpreted as millscale and, therefore, represents SSPC-SP 14 and does not represent SSPC-SP 6.ISO photographs illustrating A Sa 3, B Sa 3 and C Sa 3 do not adequately illustrate the surface texture of typically blast cleaned steel.The United Kingdom Standard BS 7079 Part A1 is equivalent to ISO 8501-1 and depicts the degrees of cleanliness of unpainted steel. BS 7079 Part A2 is equivalent to ISO 8501-2 and depicts the same degrees of cleanliness of previously painted steel.

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tion. Table 3 gives the correlation between the SSPC andthe ISO pictorial standards.

5.3 SSPC-SP 3, “POWER TOOL CLEANING”: Similarto hand tool cleaning, power tool cleaning removes looserust, loose mill scale, and loose paint. Intact materials mayremain. Power tools use electrical and pneumatic equip-ment to provide faster cleaning. They include sanders, wirebrushes or wheels, chipping hammers, scalers, rotatingflaps (rotopeen), needle guns, and right angle or diskgrinders. Some have high efficiency particulate air filter(HEPA) vacuum lines attached to reduce air pollution andcollect debris produced in the cleaning operation. Powertools clean by impact, abrasion, or both. Cleaning of metalsurfaces is less expensive using power tools than usinghand tools. Also, less particulate contamination of theenvironment occurs than from abrasive blasting. Thus,power tools are used frequently for spot cleaning of dam-aged coatings, where contamination of adjacent areas byabrasive is unacceptable, and when a surface-tolerantcoating such as oil-based paint is to be used.

The power tool cleaning specification requires that oiland grease, along with any salts, be removed as specifiedin SSPC-SP 1, “Solvent Cleaning” prior to power toolcleaning. On welded work, particular care should be takento remove as much welding flux, slag, and fume deposit asis possible since these are notorious in promoting paintfailure on welded joints. All loose matter should be removedfrom the surface prior to painting. Blowing off with clean,dry, oil-free compressed air, brushing, or vacuum cleaningare satisfactory methods.

Care is necessary in the use of power tools to preventexcessive roughening of the surface as ridges and burrscan contribute to paint failure because sharp edges may notbe protected by adequate thickness of paint. Excessivepower wire brushing can also be detrimental to the perfor-mance of the paint since the surface (particularly mill scale)is easily burnished to a smooth, slick finish to which paintwill not adhere.

5.3.1 Loose Rust, Mill Scale, and Paint: Determina-tion of the degree of cleaning required to comply with thisspecification is often very difficult. The problem is in estab-lishing whether a residue is “adherent” or “loose.” Thespecification considers the residue adherent if it cannot belifted with a dull putty knife, a somewhat subjective criteria.

One possible solution is to establish a standard ofcleaning through use of a specified cleaning procedure inwhich the type of tool, force, speed, etc., are all stipulated.The surface for the standard (or the control) should be a flatportion of the surface actually to be cleaned. It is empha-sized that this establishes a standard of cleanliness, but nota production rate. As long as the surface is cleaned as wellas that in the standard cleaning, the actual production rateof cleaning is not in question. The standard is of value inresolving differences of opinion as to whether or not thesurface has been properly cleaned.

1

5.3.2 Visual Standards: If mutually agreed upon,SSPC-VIS 3, ISO 8501-1, or other visual references may beused to supplement the cleaning criteria of this specifica-tion. Table 3 gives the correlation between the SSPC andthe ISO pictorial standards.

5.4 SSPC-SP 4, “FLAME CLEANING OF NEWSTEEL”: This specification was discontinued in 1982.

5.5 SSPC-SP 5/NACE No. 1, “WHITE METAL BLASTCLEANING”: White Metal Blast Cleaning is generally usedfor exposures in very corrosive atmospheres and for immer-sion service where the highest degree of cleaning is re-quired and a high surface preparation cost is warranted.

Blast cleaning to white metal will result in high perfor-mance of the paint systems due to the complete removal ofall rust, mill scale, and foreign matter or contaminants fromthe surface. In ordinary atmospheres and general use,white metal is seldom warranted.

The use of this grade of blast cleaning without rust backis particularly difficult in the environments where it is mostneeded as a preparation for painting; for example, in humidchemical environments. White Metal Blast Cleaning shouldbe conducted at a time when no contamination or rustingcan occur, and when prompt painting is possible. A goodrule is that no more surface should be prepared for paintingthan can be coated the same day.

When a project specification includes maintenancepainting, if White Metal Blast Cleaning is specified, it willapply to the entire surface.

5.5.1 Visual Standards: If mutually agreed upon,SSPC-VIS 1-89 or other visual references may be used tosupplement the cleaning criteria of this specification. Table3 gives the correlation between the SSPC and the ISOpictorial standards. When using the photographic stan-dards, it should be recognized that the color or hue of thecleaned surface may appear different than the photographsdue to the nature of the steel, the abrasives used, thepresence of existing coatings, and other factors.

5.6 SSPC-SP 6/NACE No. 3, “COMMERCIAL BLASTCLEANING”: Commercial Blast Cleaning should be em-ployed for all general purposes where a high, but notperfect, degree of blast cleaning is required. It will removeall rust, mill scale, and other detrimental matter from thesurface, but will permit a great deal of staining from rust, millscale, or previously applied paint to remain. The surface willnot necessarily be uniform in color, nor will all surfaces beuniformly clean. The advantage of Commercial Blast Clean-ing lies in the lower cost for providing a degree of surfacepreparation that should be suitable for the majority of caseswhere blast cleaning is believed to be necessary. However,if it is possible that Commercial Blast Cleaning will result ina surface unsatisfactory for the service, then Near-WhiteBlast Cleaning or White Metal Blast Cleaning should bespecified.

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When a project specification includes maintenancepainting, if Commercial Blast Cleaning is specified, it willapply to the entire surface. If it is intended that some of theexisting coating be permitted to remain (e.g. because it isthin, well adherent, and compatible with the new coatingsystem), the contract documents should stipulate the ex-tent of the surface to be cleaned in accordance with thisspecification. SSPC-PA 1, “Shop, Field, and MaintenancePainting of Steel,” and SSPC-PA Guide 4, “Guide to Main-tenance Repainting with Oil Base or Alkyd Painting Sys-tems,” cover additional maintenance painting procedures.

5.6.1 Visual Standards: If mutually agreed upon,SSPC-VIS 1-89 or visual references may be used to supple-ment the cleaning criteria of this specification. Table 3 givesthe correlation between the SSPC and the ISO pictorialstandards. When using the photographic standards, it shouldbe recognized that the color or hue of the cleaned surfacemay appear different than the photographs due to thenature of the steel, the abrasives used, the presence ofexisting coatings, and other factors.

5.7 SSPC-SP 7/NACE No. 4, “BRUSH-OFF BLASTCLEANING”: Brush-Off Blast Cleaning should be em-ployed when the environment is mild enough to permit tightmill scale, tight paint (if the surface was previously painted),and tight rust to remain on the surface. The surface result-ing from this method of surface preparation should be freeof all loose mill scale, loose paint, and loose rust. The smallamount of rust remaining should be an integral part of thesurface. The surface should be sufficiently abraded toprovide a good anchor for paint. The low cost of this methodmay result in economical protection in mild environments.

It is not intended that Brush-Off Blast Cleaning be usedfor very severe surroundings. Brush-Off Blast Cleaning isgenerally intended to supplant power tool cleaning wherefacilities are available for blast cleaning. With this methodof surface preparation, as with any other, it is understoodthat the rate of cleaning will vary from one part of thestructure to another depending upon the initial condition ofthe surface. Because of the high rate of cleaning, the costis low relative to the higher grades of blast cleaning. Paintswhich are used should have a fair degree of wetting be-cause of the material that is allowed to remain on thesurface.

When a project specification includes maintenancepainting, if Brush-Off Blast Cleaning of the entire surface isspecified, the existing coating being cleaned should becompatible with the new coating system and should be ofadequate integrity to withstand the impact of the abrasive.If a substantial amount of the coating will be removed by thismethod, then a higher level of cleaning should be specified(e.g. Commercial Blast Cleaning). SSPC-PA 1, “Shop,Field, and Maintenance Painting,” and SSPC-PA Guide 4,“Guide to Maintenance Repainting with Oil Base or Alkyd

1

Painting Systems,” cover additional maintenance paintingprocedures.

5.7.1 Visual Standards: If mutually agreed upon,SSPC-VIS 1-89 or other visual references may be used tosupplement the cleaning criteria of this specification. Table3 gives the correlation between the SSPC and the ISOpictorial standards.

5.8 SSPC-SP 8, “PICKLING”: Pickling is considered adesirable method of removing rust and mill scale fromstructural shapes, beams, and plates when the cost of suchremoval is felt to be justified. Properly accomplished, pick-ling produces a surface that will promote long paint life withmost coatings, but pickling is most commonly associatedwith hot dipped galvanizing.

Where production is sufficiently high to keep the equip-ment in use, pickling results in low cost shop preparation. Itis impractical for field use.

Facilities are extremely limited for pickling of largefabricated members or large structural beams. However,there are a number of facilities for large steel plates andstructural members not exceedingly long. Small scale pick-ling facilities are widely available.

Hydrochloric acid dissolves scale faster than sulfuricacid, but hydrochloric acid is seldom heated because of theextreme difficulty associated with the fumes which evolveupon heating. Any acid which is used should be used witha suitable inhibitor. Considerable use is made of the duplextype of pickling where sulfuric acid is used to remove therust and scale, and phosphoric acid is used for a finalphosphate treatment. Special precautions including freshwater rinsing are necessary to remove residues of unreactedsulfuric or hydrochloric acid.

Design of fabricated steel may require special consid-eration to eliminate pockets or crevices which trap acidduring pickling. This may be avoided by pickling in phos-phoric acid. Pickled steel, like blast cleaned steel, shouldbe painted as soon as possible after cleaning. A moredetailed discussion of pickling is available in Volume 1 ofthe SSPC Painting Manual.

5.9 SSPC-SP 9, “WEATHERING FOLLOWED BYBLAST CLEANING”: This specification was discontinuedin 1971. Weathering prior to blast cleaning has been foundto be a very harmful practice, especially in corrosive envi-ronments, since deleterious surface impurities are muchmore difficult to remove after weathering away of mill scale.

5.10 SSPC-SP 10/NACE No. 2, “NEAR-WHITE BLASTCLEANING”: In many exposures involving a combinationof high humidity, chemical atmosphere, marine, or othercorrosive environment, the use of White Metal Blast Clean-ing was found to be overly expensive due to the dispropor-tionately large amount of work required to remove the last

9


vestiges of streaks and shadows. There are many applica-tions in which these traces can be tolerated without appre-ciable loss in coating life. Therefore the need for a grade ofblast cleaning beyond that of commercial but less thanWhite Metal Blast Cleaning was demonstrated. This Near-White Blast Cleaning specification was developed to fill thisneed.

Near-White Blast Cleaning should be employed for allgeneral purposes where a high degree of blast cleaning isrequired. It will remove all rust, mill scale, and other detri-mental matter from the surface but permits streaks andstains to remain. The surface will not necessarily be com-pletely uniform in color, nor will all surfaces be uniformlyclean. However, it is explicit in this specification that shad-ows, streaks, or discolorations, if any, be slight and bedistributed uniformly over the surface—not concentrated inspots or areas.

The advantage of Near-White Blast Cleaning lies in thelower cost for surface preparation that is satisfactory for allbut the most severe service conditions. Depending uponthe initial condition of the new or previously painted steel,it has been variously estimated that Near-White Blast Clean-ing can be carried out at a cost of 10 to 35% less than thatof White Metal Blast Cleaning. These numbers are esti-mates only and will not hold true in all cases.

The verbal description, calling for at least 95% of thesurface being equivalent to White Metal Blast Cleaning, isbased upon a large number of visual observations and alimited number of light reflectivity measurements. It ishoped that the amount of surface impurity can be quantifiedby specific measurement technique, but efforts to datehave been unsuccessful except on a laboratory basis. It isbelieved, however, that a visual estimate of the amount ofresiduals can be agreed upon between owner and contrac-tor.

When a project specification includes maintenancepainting, if Near-White Blast Cleaning is specified, it willapply to the entire surface. If it is intended that some of theexisting coating be permitted to remain (e.g. because it isthin, well adherent, and compatible with the new coatingsystem), the contract documents should stipulate the ex-tent of the surface to be cleaned in accordance with thisspecification. SSPC-PA 1, “Shop, Field, and MaintenancePainting of Steel,” and SSPC-PA Guide 4, “Guide to Main-tenance Repainting with Oil Base or Alkyd Painting Sys-tems,” cover additional maintenance painting procedures.

5.10.1 Visual Standards: If mutually agreed upon,SSPC-VIS 1-89 or visual references may be used to supple-ment the cleaning criteria of this specification. Table 3 givesthe correlation between the SSPC and the ISO pictorialstandards. When using the photographic standards, it shouldbe recognized that the color or hue of the cleaned surfacemay appear different than the photographs due to thenature of the steel, the abrasives used, the presence ofexisting coatings, and other factors.

5.11 SSPC-SP 11, “Power Tool Cleaning to BareMetal”: Power tool cleaning to remove tightly adherent

20

material produces a surface which is visibly free from allrust, mill scale, and old coatings, and which has a surfaceprofile. It produces a greater degree of cleaning thanSSPC-SP 3, “Power Tool Cleaning,” (which does not re-move tightly adherent material) and may be considered forcoatings requiring a bare metal substrate.

The surfaces prepared according to this specificationare not to be compared to surfaces cleaned by abrasiveblasting. Although this method produces surfaces that “look”like nearwhite or commercial blast, they are not necessarilyequivalent to those surfaces produced by abrasive blastcleaning as called for in SSPC-SP 10 (near-white) or SP 6(commercial).

The SSPC specification “Power Tool Cleaning to BareMetal” helps to bridge the gap between the marginal sur-face preparation described in SP 2 (hand tool), SP 3 (powertool), and SP 7 (brush-off) and the more thorough cleaningdescribed in SP 6 (commercial), SP 10 (near-white), andSP 5 (white metal). It gives the specifier an opportunity toselect a method of cleaning suitable for certain coatings inareas where abrasive blasting is prohibited or not feasible.Examples of circumstances where this specification may beapplied are as follows:

• touch-up of welded or damaged areas oferection assemblies;

• reducing volume of hazardous waste producedby abrasive blasting;

• cleaning around sensitive equipment or machin-ery.

5.11.1 Power Tools and Cleaning Media: A powertool cleaning system consists of a surface cleaning mediumfor abrading the surface and a powered tool for driving thatmedium. The specification distinguishes between mediathat clean the surface and those that produce a profile.Similarly, power tools are classified as surface cleaningtype or profile producing type.

Surface cleaning power tools are those that drive twomain classes of surface cleaning media: 1) non-wovenabrasive wheels and discs; 2) coated abrasive discs, flapwheels, bands, or other coated abrasive devices.

Profile producing power tools are described as thoseon which rotary impact or peening media are mounted, andthose on which steel needles (needle guns) are mounted,although other tools and media that can produce the appro-priate profile are acceptable. In instances where a profilealready exists, such as on previously painted surfaces, onlysurface cleaning power tools and media may be required,so long as the appropriate degree of cleanliness is createdwithout reducing the profile to less than 25 micrometers(one mil). Where an existing profile is reduced to less than25 micrometers (one mil) in the process of cleaning, surfaceprofile power tools are also required to be used to restorethe appropriate profile.

Where there is no existing profile, then both cleanli-


ness and profile must be produced as specified. This mayrequire using both kinds of tools and media, although insome cases a surface profiling tool/medium may adequatelyclean the surface without requiring a separate cleaningoperation with surface cleaning tools/media.

Cleaning of metal surfaces is usually faster and lessexpensive using abrasive blasting than using power tools,without considering the cost of mobilization and contain-ment for the control of dust and debris. However, powertools are used frequently for spot cleaning of damagedcoatings where contamination of adjacent areas by abra-sive is unacceptable. Less particulate contamination of theenvironment occurs than from abrasive blasting. Misuse ofpower tools on metals produces a burnished rather than atextured surface that compromises coating adhesion.

5.11.2: Power Tools With Vacuum Shrouds: Specialpower tools may also have HEPA vacuum lines attached toreduce air pollution and to contain the debris generated atthe point-source during coating removal. The vacuum shroudsurrounds only the tool itself, providing a localized contain-ment of the debris at the point of generation.

The method of operation of vacuum shrouded tools issimilar to that of non-vacuum shrouded tools. This is diffi-cult when cleaning irregular surfaces. As a result, specialcustom shrouds can be fitted onto the ends of the tools.Some tools however, are not amenable to shrouds, andtherefore the collection of debris is not as efficient. Asurface can be cleaned to comply with either SSPC-SP 3,“Power Tool Cleaning,” or SSPC-SP 11, “Power Tool Clean-ing to Bare Metal,” using these vacuum shrouded tools.

5.11.3 Visual Standards: If mutually agreed upon,SSPC-VIS 3 or other visual standard may be used tosupplement the cleaning criteria of this specification. Table3 lists the SSPC-VIS 3 photographs that correspond tovarious initial surface conditions. SSPC-VIS 1 and ISO85011 are not suitable for assessing surfaces cleaned tobare metal by power tools.

5.12 SSPC-SP 12/NACE No. 5, “SURFACE PREPA-RATION AND CLEANING OF STEEL AND OTHER HARDMATERIALS BY HIGH- AND ULTRAHIGH-PRESSUREWATER JETTING PRIOR TO RECOATING”: As is thecase with dry abrasive blast cleaning, high-pressure waterjetting (HP WJ) and ultrahigh- pressure water jetting (UHPWJ) can be used to prepare surfaces to various degrees ofcleanliness. Water jetting is used when abrasive blasting isnot possible or when it is necessary to remove a highpercentage of soluble salt contamination. Claims havebeen made that, if the job is considered as a whole, HP WJand UHP WJ are economically competitive with dry abra-sive blasting. Water jetting does not produce a profile.However, if a profile exists under old paint that is beingremoved, the original profile can be restored by water

2

jetting. Joint technical report SSPC-TR 2/NACE 6G198,“Wet Abrasive Blast Cleaning,” discusses wet methodsusing abrasive.

Water cleaning uses pressures less than 70 Mpa (10,000psi) and high-pressure water jetting (HP WJ) uses pres-sures above this value. Ultrahigh-pressure water jetting(UHP WJ) uses pressures above 170 Mpa (25,000 psi).Some members of the water jetting industry want to defineUHP WJ to be above 210 MPa (30,000 psi).

5.12.1 Surface Cleanliness: SSPC-SP 12 definesfour degrees of VISUAL cleanliness which can be summa-rized as follows:

• WJ-1 Clean to the bare substrate; the most thor-ough level

• WJ-2 Almost clean to the bare substrate; verythorough cleaning; randomly dispersed visiblestains of previously existing rust, paint, andforeign matter is allowed on only 5% of thesurface

• WJ-3 Thorough cleaning; randomly dispersedvisible stains of previously existing rust, paint,and foreign matter is allowed on only one-thirdof the surface

• WJ-4 All loose material is uniformly removed

These four conditions of water jetting were meant toparallel the four degrees of abrasive blast cleaning SSPC-SP 5 (white metal), SSPC-SP 10 (near-white), SSPC-SP 6(commercial), and SSPC-SP 7 (brush-off).

Since one of the advantages of water jetting is theremoval of soluble contaminants, SSPC-SP 12 definesthree levels of NONVISUAL surface cleanliness based onthe amount of water-soluble chlorides, iron-soluble salts,and sulfates:

• SC-1 No salts detected• SC-2 Less than 7 µg/cm2 chloride ion contami-

nants, 10 µg/cm2 ferrous ion, and 17 µg/cm2

sulfate ion• SC-3 Less than 50 µg/cm2 chloride and sulfate

contaminants

Methods for measuring the amount of salt on thesurface are described in SSPC-TU 4, “Field Methods forRetrieval and Analysis of Soluble Salts on Substrates.” Thechoice of visual and nonvisual cleanliness is determined bythe existing condition of the surface, the coating to beapplied, and the exposure environment.

5.12.2 Flash Rusting: With any wet method of surfacepreparation, the cleaned surface will eventually exhibit arust bloom or flash rust as the surface dries. Non-uniformrusting with areas of heavy rust usually indicates the pres-

1


ence of soluble salts on the surface. A uniform rust bloommay be an acceptable surface to paint. Visible flash rustingcan be light, medium, or heavy. The coating manufacturermust be consulted to determine the extent of rust bloom thattheir coating can tolerate for the given exposure. Inhibitorscan be added to the water to prevent flash rusting, but thecoating manufacturer must be consulted to verify compat-ibility with the level of inhibitor used.

5.12.3 Visual Standards: If mutually agreed upon,SSPC-VIS 4 (I) or other visual references may be used tosupplement the cleaning criteria of this specification. SSPC-VIS 4 (I)contains photographs showing steel of originalcondition of rust grade C cleaned to WJ-2 and WJ-3, eachwith light, medium, or heavy flash rusting. A parallel set ofphotographs is given for original condition of rust grade D.When using the photographic standards, it should be recog-nized that the color or hue of the cleaned surface mayappear different than the photographs due to the nature ofthe steel, the presence of existing coatings, and otherfactors.

5.13 SSPC-SP 13/NACE NO. 6, “SURFACE PREPA-RATION OF CONCRETE”: This standard gives require-ments for surface preparation of concrete by mechanical,chemical, or thermal methods prior to the application ofbonded protective coating or lining systems. The require-ments of this standard are applicable to all types ofcementitious surfaces including cast-in-place concrete floorsand walls, precast slabs, masonry walls, and shotcretesurfaces.

An acceptable prepared concrete surface should befree of contaminants, laitance, loosely adhering concrete,and dust, and should provide a sound, uniform substratesuitable for the application of protective coating or liningsystems. When required, a minimum concrete surfacestrength, maximum moisture content, and surface profilerange should be specified in the procurement documents.

This standard contains sections on definitions, inspec-tion procedures before surface preparation, the methods ofsurface preparation, inspection, and acceptance criteria forlight service and for severe service.

5.14 SSPC-SP 14/NACE No. 8, “INDUSTRIAL BLASTCLEANING”: Industrial blast cleaning is used when theobjective is to remove most of the coating, mill scale, andrust, but the extra effort required to remove every trace ofthese materials is determined to be unwarranted. Industrialblast cleaning provides a greater degree of cleaning thanSSPC-SP 7 (brush-off) but less than SSPC-SP 6 (commer-cial).

The difference between an industrial blast and a brush-off blast is that the objective of a brush-off blast is to allowas much of an existing coating to remain as possible, whilethe purpose of the industrial blast is to remove most of thecoating. The industrial blast allows defined mill scale,

22

coating, and rust to remain on less than ten percent of thesurface and allows defined stains to remain on all surfaces.A commercial blast provides a higher level of cleaning, andthe surface is free of mill scale, rust, and coatings, allowingonly random staining to remain on no more than 33 percentof each 9 in2 (60 cm2) increment of the surface.

5.14.1 Visual Standards: If mutually agreed upon,visual references may be used to supplement the cleaningcriteria of this specification. SSPC has not yet prepared avisual reference for this recently issued standard. ISO8501-1:1988 has a photograph, B Sa 2, that appears tohave islands of mill scale remaining and therefore wouldconform to SSPC-SP 14. Standard reference photographsof previously painted steel depicting SSPC-SP 14 have notyet been prepared.

6. Selection of Abrasives, Blast Cleaning Pa-rameters, and Equipment

The selection of the size and type of abrasive which willmost effectively and economically produce the desiredsurface finish is not an exact science because of the manyvariables involved. These variables include the following ata minimum:

• The nature of the steel being cleaned, i.e., thehardness and the degree of rusting which mayhave developed prior to blast cleaning.

• The basic purpose for blast cleaning, which mayinclude either new construction or maintenanceand repair programs.

• The type of surface finish desired, i.e., degree ofcleanliness and height of profile required tomeet the specification or requirement of thepaint to be applied. See SSPC report, “SurfaceProfile for Anti-Corrosion Paints,” (SSPC 74-01).

• The type of blast cleaning systems which maybe employed, e.g., centrifugal wheel or air blastrecirculating abrasive systems, or open nozzleairblasting with expendable abrasives.

In general, select the smallest size abrasive that willproduce the desired cleaning results. Usually, this will givethe fastest, most economical cleaning operation.

Non-traditional blast cleaning media may be expend-able or recyclable. Such materials include sponge, dry ice,sodium bicarbonate and ice crystals. All require specializedequipment and may or may not create a surface profile.

General information concerning the chemical and physi-cal properties of cast steel shot and grit, and the physicalproperties of various non-metallic abrasives along withinformation on their usage, are presented in the followingsections.

6.1 ABRASIVE CHARACTERISTICS: Selecting the


TABLE 4PHYSICAL DATA ON NON-METALLIC ABRASIVES

Bulk DensityHard-ness(Mohs)

Shape SpecificGravity

lb/ft3 kg/m3

Color FreeSilica

(wt. %)

Degree ofDusting

Reuse

Naturally Occurring AbrasivesSilica Sand 5 Rounded 2 to 3 100 1600 White 90 + High PoorHeavyMineral Sand

5 to 7 Rounded 3 to 4 125 2000 Variable < 5 Medium Good

Flint 6.5 to 7 Angular 2 to 3 80 1300 Lt. Gray 90 + Medium GoodGarnet 7 to 8 Angular 4 145 2300 Pink Nil Medium GoodZircon 7.5 Cubic 4.5 185 3000 White Nil Low GoodNovaculite 4 Angular 2.5 100 1600 White 90+ Low Good

By-Product AbrasivesBoiler Slag 7 Angular 2.8 85 1400 Black Nil High PoorCopper Slag 8 Angular 3.3 110 1800 Black Nil Low GoodNickel Slag 8 Angular 2.7 85 1400 Green Nil High PoorWalnutShells

3 Cubic 1.3 45 720 Brown Nil Low Poor

Peach Shells 3 Cubic 1.3 45 720 Brown Nil Low PoorCorn Cobs 4.5 Angular 1.3 30 480 Tan Nil Low Good

Manufactured AbrasivesSiliconCarbide

9 Angular 3.2 105 1700 Black Nil Low Good

AluminumOxide

8 Blocky 4.0 120 1900 Brown Nil Low Good

Glass Beads 5.5 Spherical 2.5 100 1600 Clear 67 Low GoodCrushedGlass

6 to 8 Irregular 2.5 63 to91

1000-1500

Gray 67 Low Poor

SodiumBicarbonate

2.5 Powder 2.2 60 960 White Nil None Poor

Sponge 0.016 Granular 0.29-1.45 5 to25

80 to400

Various Nil Low Good

PlasticBeads

3.5 Blocky 55 880 Various Nil Low Fair

Dry Ice Nil Cylinder 62.4 50 800 White Nil Low Poor

appropriate type of abrasive for the job is important be-cause the type of abrasive can have a significant influenceon the appearance of the blast cleaned surface, productiv-ity, and subsequent clean-up. Abrasives vary in hardnesses,particle size distribution, shape, bulk density, friability,waste generation, and recyclability. The following is adiscussion of these characteristics and how these charac-teristics influence abrasive performance. Some physicaldata on non-metallic abrasives are given in Table 4.

6.1.1 Hardness: Metallic abrasive hardness is mea-sured on the Rockwell C scale while non-metallic abrasivehardness is measured on the Mohs scale. Hardness isimportant because the harder an abrasive, the more profileit is likely to generate.

6.1.2 Size: Most abrasive specifications include some

2

form of particle size designation, because particle sizeplays a major role in productivity and in the subsequentprofile generated. The role of abrasive size will be dis-cussed in more detail under the section dealing with pro-ductivity.

6.1.3 Shape: Abrasive particles range from spheri-cal to sharply angular. Spherical to rounded particles cleanby impact, producing a peened surface. Angular to irregu-larly shaped particles clean by scouring or cutting thesurface, producing an etched surface.

6.1.4 Bulk Density: The bulk density of an abrasive isa measure of an abrasive’s weight per unit volume and isusually expressed in kilograms per cubic meter or poundsper cubic foot. For example, the bulk density of sand isapproximately 160 kg/m3 (100 lb/ft3) whereas for steel gritabrasives, it is typically 400 kg/m3 (250 lb/ft3). Bulk density

3


is important when lifting abrasive filled bulk containers.Using the bulk density values for sand and steel shownabove, a 2.8 m3 (100 ft3) container filled with sand weighs4500 kg (5 tons), whereas the same container filled withsteel grit weighs 11,000 kg (12.5 tons).

6.1.5 Friability/Waste Generation: Abrasive friabilityis a measure of an abrasive’s resistance to break down onimpact. The more friable an abrasive, the greater thetendency for the abrasive to break down on impact, therebygenerating more waste and dust.

6.1.6 Recyclability: Recyclability is a property of anabrasive that allows it to be reused many times withoutexcessive breakdown. In order to meet the strict cleanli-ness requirements for recycling, the abrasive must also beable to withstand the rigorous cleaning process for removalof contaminants from the abrasive mix. Most mineral andbyproduct abrasives can be recycled one to three times, butthey have difficulty meeting the strict cleanliness require-ments for recycling. Steel abrasives, on the other hand,show the lowest friability, generate the least amount ofwaste, can be recycled many times, and meet the strictcleanliness requirements for recycling.

6.2 FACTORS AFFECTING SURFACE PROFILE: Sur-

face profile is a measure of surface roughness resultingfrom abrasive blast cleaning. The height of the profileproduced on the surface is measured from the bottoms ofthe lowest valleys to the tops of the highest peaks.

The thickness and generic type of paint to be applieddetermines the allowable minimum and maximum profileheight. The abrasive size is then chosen to achieve thatprofile. SSPC-AB 1, “Mineral and Slag Abrasives,” definesfive abrasive grades yielding profile heights from 13 to 150micrometers (0.5 to 6.0 mils).

SSPC studies have shown that metallic abrasiveslarger than those which will pass through a #16 screen(ASTM E 11) may produce a profile which is too deep to beadequately covered with a single coat of primer. Accord-ingly, it is recommended that the use of larger abrasives beavoided whenever possible. However, when heavy mill

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scale or rust are present, abrasives of a larger size may beneeded. In these cases two coats of primer may be neededinstead of the usual one coat. Alternatively, if the nozzlepressure is increased, a smaller size abrasive may removeheavy paint or scale more effectively than a larger abrasiveat the lower pressure. Higher nozzle pressures may stillproduce larger profiles.

Table 5 gives the range of maximum and averagemaximum profile heights to be expected under normal goodoperating conditions (wheel and nozzle). At nozzle pres-sures in excess of 760 kPa (110 psi), the profile may besignificantly higher.

Profile comparators are available to aid in estimatingthe average maximum profile of surfaces blasted with sand,steel grit, and steel shot. Surface profile can also bemeasured by use of replica tape. Methods for measuringprofile are described in ASTM D 4417, “Test Method forField Measurement of Surface Profile of Blast CleanedSteel” and in NACE RP0287, “Field Measurement of Sur-face Profile of Abrasive Blast Cleaned Steel Surfaces Usinga Replica Tape.” A report, “Surface Profile for Anti-Corro-sion Paints,” (SSPC 74-01) is available from SSPC describ-ing methods of measuring profile and relating profile toblast cleaning conditions and to coating performance.

When the abrasive media impacts the surface it gener-ates surface profile. It is this profile or anchor pattern thatis necessary for most coating systems to adhere to thesubstrate. The depth of the profile is controlled by thefollowing parameters:

• Abrasive Size: The larger the abrasive, thelarger the profile.

• Abrasive Type: Angular abrasives create adeeper profile than round abrasives of the samesize.

• Hardness: The harder the abrasive the deeperthe profile.

• Blast Nozzle Air Pressure: The higher the nozzlepressure the deeper the profile.

• Type of Blast Nozzle: A venturi nozzle generatesa deeper profile than a straight bore nozzle withthe same diameter opening.

yTABLE 5

APPROXIMATE PROFILE HEIGHT OF BLASTED STEEL USING DIFFERENT SIZE ABRASIVES

Abrasive Profile height25 µm1 mil

37 µm1.5 mil

50 µm2 mil

63 µm2.5 mil

75-100 µm3 - 4 mil

Silica sand 30/60 mesh 16/35 mesh 16/35 mesh 8/35 mesh 8/20 meshSteel grit G80 G50 G40 G40 G25Steel shot S110 S170 S280 S280 S330Garnet 80 mesh 36 mesh 36 mesh 16 mesh 16 meshAluminum oxide 100 grit 50 grit 36 grit 24 grit 16 grit

These profile heights are typical if the nozzle pressure is between 620 and 700 kPa (90 and 100 psi).


• Distance of Blast Nozzle to Surface: The closerto the work the deeper profile.

• Angle of Blast Nozzle to Surface: The greaterthe angle from the perpendicular to surface, theless the profile.

Altering any of these parameters during the blastingoperation could affect profile and surface cleanliness. Toavoid undesirable changes in profile and surface cleanli-ness, blasting trials are recommended before changing anyof the parameters noted above.

6.3 PARAMETERS THAT AFFECT PRODUCTIVITY:The productivity of abrasive blast cleaning is determinedprimarily by the eleven parameters described below.

6.3.1 Particle Size: Decreasing abrasive particle sizecan dramatically increase cleaning rate. Increasing abra-sive particle size may be necessary to remove heavycoatings and scale. The general rule is to use the smallestsize abrasive that will do the job.

6.3.2 Hardness: Generally, the harder the abrasive,the better it will perform. However, very hard abrasivesshatter on impact expending most of their energy in particlebreakdown and dust generation. As with selecting abrasivesize, the general rule is to select the minimum abrasivehardness that will effectively do the job.

6.3.3 Shape: Rounded particles are most effective inremoving brittle coatings such as mill scale, whereas angu-lar or irregular shaped particles are more effective in re-moving softer coatings such as rust and paint.

6.3.4 Specific Gravity: The higher the specific gravity,the more energy a given size abrasive particle will impart tothe surface on impact and thus the more productive work itwill do. Generally, a higher specific gravity implies a higher

bulk density.

6.3.5 Nozzle Pressure: The higher the nozzle pres-sure the more productive the blast operation. For example,for each 7 kPa (1 psi) increase there is a 1.5 percentincrease in productivity. Most equipment for dry abrasiveblasting has a practical upper limit of 1000 kPa (150 psi).Due to losses, the actual maximum nozzle pressure will beless than this.

6.3.6 Nozzle Type: It is important to choose the rightnozzle for the job. For example, straight bore nozzles givea tight blast pattern that is best suited for blast cleaningsmall areas such as hand rails, spot blasting, weld seams,etc. Venturi bore nozzles create a wide blast pattern andare best suited for large area blast cleaning. Venturi borenozzles increase nozzle velocity by as much as 100% andtherefore are 35% more efficient compared to straight bore

2

nozzles of the same diameter.

6.3.7 Nozzle to Surface Distance: For optimum clean-ing rate the nozzle to surface distance is around 46 cm (18inches). However, this distance can vary depending on thetype of surface contamination being removed, nozzle pres-sure, abrasive type, and nozzle type.

6.3.8 Impact Angle: An 80 to 90 degree angle is bestsuited for removing mill scale or heavy rust and for cleaningpitted areas; a 45 to 60 degree angle is best for peelingheavy layers of paint or rust; a 60 to 70 degree angle isrecommended for general cleaning.

6.3.9 Abrasive Metering: Each abrasive type has adifferent optimum flow rate through the metering valve.Before starting any blast cleaning job, it is important toconduct a test blast with the metering valve set at lean,moderate, and high abrasive flow rates to find the optimumflow for the given abrasive.

6.3.10 Abrasive Cleanliness: A clean, dry, dust-freeabrasive is essential for optimum productivity. Check theabrasive before starting a job and regularly thereafter forforeign matter, moisture, and dust.

6.3.11 Embedment: Some abrasive products, particu-larly non-metallics, tend to embed in the blast cleanedsurface. Conduct a test blast with the abrasive and evaluatethe blast cleaned surface to be sure the amount of embed-ment does not exceed the job specification requirements.

6.4 ABRASIVE TYPES: Abrasives, the material in theblasting operation that does the work, can be divided intotwo major categories: metallic, generally ferrous, abrasivesand nonmetallic abrasives. The non-metallic abrasives canbe further subdivided into naturally occurring, by-product,or manufactured abrasives.

6.4.1 Metallic Abrasives: Steel shot consists of nearlyspherical particles of steel obtained by granulating a moltenstream of metal with water, air, or other methods. Steel shotwill generally conform to SSPC-AB 3 “Newly Manufacturedor Re-Manufactured Steel Abrasives” in terms of hardness,chemical composition, size, and microstructure.

Cast steel grit consists of angular particles producedby crushing steel shot (SAE J827). Steel grit is available ina wide range of hardnesses, from 30 to 66 on the RockwellC-scale (R

c), produced by varying the tempering time cyclesto which the grit is subjected. Generally, the three hardnessesmost commonly produced are in the ranges of 40 to 50 Rc,55 to 60 Rc, and 60 to 66 Rc. The first two hardness rangesare used for structural steel, and the latter is used primarilyfor selective application where deep, consistent, sharpetched finishes are required, or where moderate etches onextremely hard surfaces are needed.

5


Steel shot will produce a peened surface texturewhereas steel grit produces more of an etched surfacetexture. The etch becomes more pronounced with increas-ing abrasive hardness.

Typical applications of various steel abrasives, refer-ring to rust grade classifications described in Section 4.1are:

• Shot: Commonly used on new steel to removemill scale using centrifugal wheel machines

• Grit (40-50 Rc): Most effective on rust grades Cand D, but also commonly used for rust grades Aand B

• Shot/Grit Mixture (Shot 40-50 Rc/Grit 55-60 Rc):Used on new steel to remove both mill scale andrust. Shot/grit mixes demand careful attentionand close control of abrasive additions by theoperator to maintain the shot/grit ratio.

6.4.2 Non-Metallic Abrasives: Non-metallic abrasivescan be categorized as naturally occurring, by-product, ormanufactured. Naturally occurring abrasives include silicasand, olivine sands, staurolite and other minerals, flint,garnet, zirconium, and novaculite. Byproduct abrasivesinclude those from smelters (i.e., nickel or copper slag) andutility generators (coal or boiler slag) and those from agri-cultural products (e.g., walnut shells, peach shells, orcorncobs). Manufactured abrasives include silicon carbide,aluminum oxide, and glass beads.

Commonly used abrasives for surface preparation ofsteel to be painted are silica sand, coal and smelter slags,staurolite, olivine, and garnet. Some countries have bannedthe use of abrasives with a high free-silica content becauseof possible health hazards. The United States militaryspecification MIL-A-22262(SH), “Abrasive Blasting Media,Ship Hull Blast Cleaning,” allows the maximum crystallinesilica content of the abrasive to be 1.0 percent by weight.This level of silica corresponds to a Class A abrasive asdescribed in SSPC-AB 1, “Mineral and Slag Abrasives.”

6.5 BLAST EQUIPMENT: For the most economicalproduction, the blast cleaning equipment must match thejob.

6.5.1 Conventional Blasting: Air abrasive blastingequipment has five basic components: air compressor, airhose, blasting machine (sand pot), blast hose, and nozzle.The compressor must be large enough to supply the volumeof air needed at the correct pressure, and this depends onfactors such as nozzle size, number of nozzles, and lengthand size of air hose. Nozzles are available in severallengths, designs, sizes of openings, and lining materials.Nozzle lengths of 13 to 20 cm (5 to 8 inches) are generallyused for removing tightly adhering rust and scale. Shorternozzles 8 cm (3 inches) or less are more appropriate for usebehind beams and in other inaccessible places.

26

Where shop cleaning of steel is possible, centrifugalwheel blasting units using recyclable steel abrasive are themost economical. Both centrifugal wheel and air blastingare discussed in detail in Volume 1 of the SSPC PaintingManual.

Non-traditional blast cleaning media (sponge, dry ice,sodium bicarbonate, ice crystals) may be expendable orrecyclable and may or may not create a surface profile. Allrequire specialized equipment (see Section 9).

6.5.2 Vacuum Blasting: Vacuum blast cleaning is lessproductive than conventional blast cleaning and thereforeis used for small localized areas. Vacuum blast cleaningcan achieve the highest levels of surface preparation whileminimizing worker exposure to emissions of dust and de-bris. The tools must be properly operated and fitted with theappropriate shroud in order to maintain the seal betweenthe blast nozzle and the substrate. Compressed air is usedto propel abrasive particles against the surface to be cleaned.The blast nozzle is fitted into a localized containmentassembly (surrounding the nozzle only) which is equippedwith a vacuum. Dust, abrasive, and old paint are sent to arecycler. The cleaned abrasive is returned for re-use. Me-tallic abrasives such as steel grit, steel shot, or aluminumoxide are used.

6.5.3 Abrasive Blast Cleaning Above 760 kPa (110psi): Over the last several years many blast cleaningoperators have been developing techniques that will allowthem to blast clean at nozzle pressures greater than 760kPa (110 psi). The primary driving force has been dramaticincreases in productivity. For every 7 kPa (1 psi) increasein nozzle pressure there is a 1.5 percent increase in produc-tivity. For example, going from 690 to 760 kPa (100 to 110psi) is a 10 percent increase in nozzle pressure but a 15percent increase in productivity. Going from 690 to 860 kPa(100 to 125 psi) results in a 38 percent increase in produc-tivity.

Another important advantage of higher nozzle pres-sures is the ability to use finer abrasives to achieve a givenprofile. Using finer abrasives means more abrasive impactsper unit time, which translates into faster cleaning andhigher productivity. Steel abrasives are recommended forhigh pressure blasting because they do not break down atthese elevated pressures. When using non-metallic abra-sives at elevated pressures, much of the energy impartedto the abrasive particles is dissipated in the pulverizing ofthe abrasive particles, thus reducing cleaning efficiencyand dramatically increasing dust levels.

7. Summary of SSPC Abrasive Specifications

7.1 SSPC-AB 1, “MINERAL AND SLAG ABRASIVES”:This specification defines the requirements for selectingand evaluating nonmetallic mineral and slag abrasivesused for blast cleaning steel and other surfaces for painting.


The specification defines two types: 1) natural mineralabrasives, including sand, flint, garnet, staurolite, and oliv-ine; and 2) slag abrasives, including coal slag, copper slagor nickel slag. The abrasives covered by the specificationare primarily intended for one-time use without recycling.

The abrasives are also classified based on the crystal-line silica content and the profile produced by the abrasive.The surface profile is determined by a blasting test con-ducted on 61 cm x 61 cm (2 ft by 2 ft) steel plates. Otherproperties stipulated include specific gravity, hardness,weight change on ignition, water-soluble contaminants,moisture content, and oil content.

For a given abrasive type, the surface profile is deter-mined by the size and shape of the abrasive particles. Theabrasive supplier is required to furnish a representativesieve analysis of the abrasive used in the profile determina-tion. This sieve analysis then becomes the typical particlesize distribution for subsequent delivery of the abrasive.Additional information on physical properties of non-metal-lic abrasives is given in Table 4.

7.2 SSPC-AB 2, “SPECIFICATION FOR CLEANLI-NESS OF RECYCLED FERROUS METALLIC ABRA-SIVES”: This specification gives the cleanliness require-ments for recycled work mix ferrous metallic abrasives. Thelimits and test methods are given for non-abrasive residue,lead content, water-soluble contaminants, and oil content.

7.3 SSPC-AB 3, “NEWLY MANUFACTURED OR RE-MANUFACTURED STEEL ABRASIVES”: This specifica-tion defines the physical and chemical requirements forsteel abrasives. Abrasive size is determined by the sieveanalysis of SAE J444, “Cast Shot and Grit Size Specifica-tions for Peening and Cleaning.” Abrasive shape, dividedinto shot or grit, is determined by the shape of 90 percent ofthe sample. The minimum specific gravity is 7.0. After 100cycles in a durability test, 80 percent must be retained onthe appropriate take-out screen. Chemical properties in-clude requirements for iron, carbon, manganese, and phos-phorous content as well as conductivity and cleanliness.

8. Wet Abrasive Blast and Water Jetting Meth-ods

Methods of coating removal which involve water may ormay not include abrasive. Several wet abrasive blast meth-

2

ods are described in SSPC-TR 2/NACE 6G198, “SSPC/NACE Joint Technical Report, Wet Abrasive Blast Clean-ing.” The specification for water jetting without abrasives isthe joint surface preparation standard SSPC-SP 12/NACENo. 5, “Surface Preparation and Cleaning of Steel andOther Hard Materials by High- and Ultrahigh-PressureWater Jetting Prior to Recoating.” The joint visual standardis SSPC-VIS 4(I)/NACE No. 7, “Interim Guide and VisualReference Photographs for Steel Cleaned by Water Jet-ting.” SSPC and NACE restrict the terms “blast” or “blast-ing” to refer to processes that involve abrasives. If noabrasives are present, the preferred terms are cleaning orjetting.

In the past, the term “water blasting” has genericallyreferred to the use of 34 to 170 MPa (5,000 to 25,000 psi)water for cleaning where abrasives may or may not beadded. Currently in SSPC, the term “water blasting” indi-cates that an abrasive has been added to the water stream;it is not used as a defined term in either wet abrasive blastor water jetting documents.

8.1 WATER CLEANING AND WATER JETTING WITH-OUT ABRASIVE: Surface contaminants from a surface canbe cleaned with water at pressures from 0.1 to over 300MPa (15 psi to 45,000 psi). Water cleaning in its mostgeneral sense is simply removal of surface contaminantssuch as dirt, soil, and salts from a surface with liquid water.The definitions of low, high, and ultra-high pressure and theuse of “cleaning” compared to “jetting” are based on thenozzle pressure and are related to the water velocity.Pressures below 34 MPa (5,000 psi) are defined as low;pressures above 34 MPa (5,000 psi) are defined as highpressure. The term “jetting” is used when the velocity of thewater exceeds 335 m/s (1100 ft/s) which occurs around 70MPa (10,000 psi). See Table 6.

8.1.1 Degrees of Cleaning: Joint surface preparationstandard SSPC-SP 12/NACE No. 5 (water jetting) definesfour degrees of visual cleaning based on the amount ofvisible contaminants remaining and three levels of cleanli-ness based on the amount of nonvisible soluble salt con-tamination that remains. SSPC-SP 12/NACE No. 5 (waterjetting) does not relate water pressure nor volume to thedegree of visual cleaning.

The visual appearance of a surface cleaned by watery

TABLE 6DEFINITIONS OF WATER CLEANING AND WATER JETTING

Low-Pressure Water Cleaning (LP WC) Less than 34 MPa (less than 5,000 psi)High-Pressure Water Cleaning (HP WC) 34 to 70 MPa (5,000 to 10,000 psi)High-Pressure Water Jetting (HP WJ) 70 to 170 MPa (10,000 to 25,000 psi)Ultrahigh-Pressure Water Jetting* (UHP WJ) Over 170 MPa (over 25,000 psi)

*Joint surface preparation standard SSPC-SP 12/NACE No. 5 is in revision in 2000 and will most likely change theUHP WJ definition to over 210 MPa (30,000 psi) instead of over 170 MPa (25,000 psi).

7


can appear very different from an abrasive blast. If thecoating to be removed is intact, the resultant surface willlook like the original blasted surface, but darker and dull. Ifthe coating is breached or there is rust to be removed, thesurface can be mottled or very non-uniform. Every defect isrevealed. It can show variation in texture, shade, color,tone, pitting, or flaking. A brown-black discoloration of ferricoxide can remain as a tightly adherent thin film on corrodedor pitted steel.

Because water cleaning and water jetting are used inmaintenance, not on new steel, the coating manufacturershould be contacted for details of coating performance overresidual paint, rust, and mill scale.

Water cleaning and water jetting have the advantage ofremoving soluble salts that can later cause underfilm corro-sion or osmotic blistering of the coating. As with any wetcleaning method, it may be necessary to add a soluble saltremover or corrosion inhibitor to the water or a rinse waterwash to achieve the desired nonvisual cleanliness.

8.1.2 Profile: Because water jetting does not providean anchor pattern needed for coating adhesion, watercleaning or water jetting is used primarily for recoating orrelining projects where there is an adequate preexistingprofile. Water alone, under various pressures, can be usedto remove coating materials, deleterious amounts of water-soluble surface contaminants, rust, shot-creting spatter,and surface grease and oil. It can not remove tight mill scaleor tightly adherent magnetite. An existing profile under thepaint or rust can be restored down to the bottom of the pits.

8.1.3 Water Consumption: Low pressure water clean-ing is often called pressure washing or power washing.Pressure washing of an existing coating is done to removesalts and surface contaminants (chalk, dirt, etc,) prior to“cleaning” the surface for painting. The water may or maynot include the use of a soluble salt remover to aid in theremoval of salts and surface contaminants. Cleaning steelfor coatings can be achieved with water pressures as greatas 300 MPa (45,000 psi) or above and water volumes ofonly 6 to 55 liters (1.5 to 15 gallons) per minute. Cautionmust be maintained with water cleaning or water jetting toavoid injuries to personnel and structures.

8.1.4 Equipment: Vacuum shrouds, remote controls,filtration, and collection, in both manual and non-manualsystems, are available. The water stream can be combinedwith a vacuum system to remove the water from the surfaceimmediately, thereby preventing flash rust. After filtrationthe water is then recycled. Dust emissions are low becausethe particulates are wetted and do not disperse in theatmosphere. The environmental risk is low as long as thewater is properly contained or collected.

8.1.5 Flash Rust: Flash rusting is defined in SSPC-VIS

28

4(I)/NACE No. 7 “Interim Guide and Visual ReferencePhotographs for Steel Cleaned by Water Jetting.” Flashrust and rust bloom are evaluated separately from visualcleanliness prior to recoating. If the surface is cleaned bywater jetting, the uniform rust bloom may not be a problemprovided the desired nonvisible cleanliness is achievedand verified by testing. Section 7.3 is a more thoroughdiscussion of flash rusting.

8.2 WET ABRASIVE BLAST CLEANING: The meth-ods, equipment, and other features of wet abrasive blastcleaning are described in SSPC-TR 2/NACE 6G198, “WetAbrasive Blast Cleaning.” Two systems for wet abrasiveblast cleaning are described: pressurized water/abrasiveblasting, which uses water to propel the abrasive, and air/water/abrasive blasting, which uses compressed air topropel the abrasive. The system processes range frommostly abrasive with a small amount of water to mostlywater with a small amount of abrasive.

Wet abrasive blasting is a process that can producesurface cleanliness and anchor patterns (surface rough-ness) similar to those obtained with dry abrasive blasting.The level of surface preparation specified is the same as ifdry abrasive blasting was the process being used, that isSSPC-SP 5, SP 10, SP 6, SP 14, and SP 7. However,because the visual appearance of wet abrasive blastedsurfaces is not necessarily the same as the visual appear-ance of dry abrasive blasted surfaces, care and judgmentshould be exercised by inspectors. There is a separatevisual guide under preparation for wet abrasive blasting.Acceptable variations in appearance that do not affectsurface cleanliness include variations caused by type ofsteel, original surface condition, thickness of the steel, weldmetal, mill or fabrication marks, heat treating, heat affectedzones, blasting abrasives, and differences due to blastingtechnique.

Surfaces cleaned by wet abrasive blasting typicallyappear darker and duller in appearance than surfacescleaned with the same abrasive in dry abrasive blasting.Wide variations in appearance can be observed amongabrasives within a given generic class. See SSPC-VIS 1-89for illustrative photographs for dry blasting.

When the surface is still damp or wet, it will appeardarker, and defects and variations in shading are magni-fied. As the surface dries, streaks will form which are notnecessarily depicted in small unit size photographs, butwhich can be clearly seen on larger areas.

Wetted abrasive should be removed from the substrateafter blasting. This is frequently accomplished with a lowpressure water cleaning to which a soluble salt removerand/or inhibitor has been added.

8.2.1 Air/Water/Abrasive Blasting: Air/water/abra-sive blasting is a cleaning method in which water is injectedinto the air/abrasive stream generated by conventional


airpressurized abrasive blasting equipment, or in which thepremixed abrasive/water combination is forced into theblast air stream generated by a conventional air compres-sor. Other generic terms to describe specific air/water/abrasive blast cleaning methods are water shroud blasting,wet-head blasting, wet blasting, low volume water abrasive

blasting, and slurry blasting.Water helps to remove contaminants from the sub-

strate, to wet the abrasive, and to substantially reducedispersion of fine particulates (dust). Particulates are oftencaused by the breakup of the abrasives, surface corrosionproducts, and paint if the surface has been previouslypainted. Dust suppression is achieved by thoroughly wet-ting the abrasive and other particles to encapsulate themwith a thin film of moisture. The objective is to removecontaminants and suppress the dusting effect caused bythe impact of the abrasive on the substrate, while retainingthe blasting characteristics of dry abrasive, including cre-ation of an anchor profile.

The equipment used for wet abrasive blasting gener-ally consists of conventional dry abrasive blasting equip-ment supplemented with modules to inject water into theabrasive stream, or specialized equipment that creates anabrasive/water slurry that is forced into the compressedblast air stream. Several methods exist for introducingwater into the air stream. With radial water injectors (waterrings) and coaxial water injectors, water is injected near theblast nozzle. A new hybrid process, introduced after SSPC-TR 2 was published, mixes a conventional abrasive airstream with water jets up to 240 MPa (35,000 psi) at thenozzle. The volume of abrasive can be varied.

With slurry blasters, the water is injected into the air/abrasive stream at some point substantially upstream fromthe blast nozzle or at the abrasive hopper, rather than at thenozzle. In the low volume, low pressure water abrasiveblasting system, four parts of abrasive are wetted with onepart of water in a hopper. This slightly wetted abrasive iscarried in a conventional compressed air stream and pro-duces results very similar to dry abrasive blasting. There isminimal water run-off.

8.2.2 Water/Abrasive Blast Cleaning: The methods,equipment, and other features of water/abrasive blast clean-ing are described in SSPC-TR 2/NACE 6G198, “Wet Abra-sive Blast Cleaning.” Water/abrasive blast cleaning is acleaning method in which abrasive is injected into the waterstream generated by conventional fluid pumps. Other ge-neric terms to describe specific water/abrasive blast clean-ing methods are slurry blasting, abrasive water jet (AWJ), orabrasive injected water jetting/blasting (AIWJ).

The typical devices used for this method of cleaningconsist of a fluid pump with a Venturi nozzle of some typein which the water flow draws the abrasive into the waterstream or the abrasive media is injected into the waterstream under pressure. The addition of expendable abra-

2

sives to high pressure water jets improves the productivityof the technique, enables the removal of intact materials,and facilitates the creation of a surface profile.

Because the fluid stream is well defined, these devicesusually cut a narrow blast pattern. However, a new hybridprocess, introduced after SSPC-TR 2 was published, mixesa conventional abrasive air stream using 0.2 to 1.1 kg/min(0.5 to 2.5 pounds/min) with the water jet stream up to 240MPa (35,000 psi) at the nozzle. It uses both a conventionalfluid pump and a compressed air stream and produces adiffuse spread pattern.

8.3 FLASH RUST AND INHIBITORS: Steel that iscleaned with water can rust rapidly. The rate of re-rustingwill depend on the purity of the water, the amount of oxygendissolved in the water, the amount of ionic species left onthe surface, the temperature, and the drying time. In 1991,G.C. Soltz reported that steel will not rust in 100% relativehumidity if all of the salts are removed. [G.C. Soltz,“TheEffects of Substrate Contaminants on the Life of EpoxyCoatings Submerged in Sea Water,” National ShipbuildingResearch Program, March 1991.] Soluble salt removersand/or inhibitors can be added to the water during thecleaning process to reduce the potential of flash rusting.The use of low conductivity water with the removal of allsalts (as measured by field tests) will significantly reducethe amount of flash rust. The amount of flash rust also canbe significantly reduced with the addition of forced airdrying or use of a vacuum shroud which does not allow thewater to remain on the surface as it is drying.

Flash rusting or rust bloom is a light oxidation of thesteel, which occurs as wetted cleaned steel dries off. Flashrusting can form quickly to change the initial appearance. Itis not the rust itself, but the source of the re-rusting that isof concern to the coating manufacturers, as inert ironoxides (rust) are used as pigments. Very dark, splotchy rustspots which appear to be isolated in localized areas usuallyindicate that ionic contaminants are left in pits, under metallips, or in crevices. These non-visible contaminants arefound to be detrimental to coating performance. A light,easily removed rust bloom is considered inert and a sign ofgeneral steel oxidation. Manufacturers can have concernsabout performance when their coatings are applied overloose dust or loose rust. The level of rust bloom that can betolerated in a given environment must be determined for thecoating systems by the coating manufacturers.

Flash rusting is not addressed in the dry abrasive blastcleaning standards except in the notes. Re-rusting of dryabrasive blasted steel, as there is little moisture present, isa sign that non-visible contaminants have been left on thesteel and is still not tolerated by the coatings manufactur-ers. G.C. Soltz has found that, for abrasive blasting, coatingthe surface before it has re-rusted is no assurance that thecoating performance will not be compromised. [G.C. Soltz,“Understanding How Substrate Contaminants Affect the

9


Performance of Epoxy Coatings and How to MinimizeContamination,” SSPC 1998 Proceedings, “Increasing theValue of Coatings”, pp. 208-219.]

Flash rusting by water is addressed in SSPC-VIS 4(I)/NACE No. 7, “Interim Guide and Visual Reference Photo-graphs for Steel Cleaned by Water Jetting.” The referencephotographs depict steel with light, medium, or heavy flashrusting prior to re-coating. Depending on the particularcoating and exposure environment, the coating manufac-turer may allow flash rusting at one of these levels. TheSSPC report, “Maintenance Coating of Weathering Steel,”(92-08), found that coatings can perform quite well over ablasted surface that has a uniform rust bloom.

Inhibitors and/or soluble salt removers can be added tothe water or to a rinse water to temporarily prevent rustformation. Environmental and health concerns in recentyears have prompted changes in the chemistry of rustinhibitors. Acceptable rust inhibitors include polyphosphates,volatile amines, benzoates, nitrites, surface tension reduc-ers, and other proprietary compounds which are formulatedin water-borne paints to reduce rust bloom. Additives suchas soluble salts or film formers can adversely affect thelong-term performance of the coating system. If an additiveis used in the water, it is imperative that the user check withthe coating manufacturer about the compatibility of thecoating with the inhibitor or soluble salt remover. Thiscompatibility can be checked using ASTM D 5367, “Prac-tice for Evaluating Coatings Applied over Surfaces Treatedwith Inhibitors Used to Prevent Flash Rusting of Steel WhenWater or Water/Abrasive Blasted.” At the present timemany coatings manufacturers prefer placing their coatingsover light flash rust rather than adding the uncertainty of aninhibitor or soluble salt remover.

9. Other Cleaning Methods

9.1 CHEMICAL STRIPPING: Paint strippers are fre-quently used to remove paint from industrial structures.Alkaline strippers are more effective in removing oil-based

30

paints, and solvent type strippers are more effective inremoving latex paints. Other coating types require bondbreaking strippers which may be composed of a blend ofsolvents comprised of compounds such as N-methylpyrrolidone (NMP) or dibasic ester (DBE). It may benecessary to use both types to strip alternating layers of oiland latex coatings from a surface. Strippers usually containa thickener to provide more contact time for solvent orchemical attack on the paint. Some are covered with asheet of plastic to increase the contact time. Chemicalstripping is one method of removing old, lead-containingpaint.

An alkaline (caustic) based or solvent based chemicalstripper is applied to the surface using trowels, brushes,rollers, or spray application. After the specified dwell time,the stripper is removed using traditional scrapers, althoughwater cleaning or ice blasting can be used. Mill scale andrust are not removed, and a profile is not generated, but anexisting profile can be restored.

The specific type of stripper must be selected basedupon the generic type of the existing coating system as wellas health, safety, and environmental concerns. Some of thestrippers require a minimum four hours set time whileothers may require a full day. In addition, many of thesolvent strippers involve chemical reactions which gener-ate heat. This heat must be contained in order for thechemical reaction to continue, which may require covers ifambient temperatures are too low.

Paint strippers, applied to horizonal or vertical surfacesby brush or spray, are covered by Federal Specification TT-R-251, “Remover; Paint (Organic Solvent Type)”; Types Iand II are flammable, Types III and IV are nonflammable;and each has two classes, A, low viscosity and B, highviscosity. These are performance specifications and in-clude the conventional paint strippers. Many paint strippersare available for the complete immersion of painted sur-faces, but these are generally specialty items.

Once the strippers have performed the desired soften-ing of the existing coating system, they are frequently

y

TABLE 7REFERENCE PHOTOGRAPHS IN SSPC-VIS 4 (I)

InitialCondition

Degree ofCleaning

Flash Rusting

SSPC-SP 12 None Light Medium HeavyRust Grade C WJ-2 C VIS WJ-2 C VIS WJ-2 L C VIS WJ-2 M C VIS WJ-2 H

WJ-3 C VIS WJ-3 C VIS WJ-3 L C VIS WJ-3 M C VIS WJ-3 HRust Grade D WJ-2 D VIS WJ-2 D VIS WJ-2 L D VIS WJ-2 M D VIS WJ-2 H

WJ-3 D VIS WJ-3 D VIS WJ-3 L D VIS WJ-3 M D VIS WJ-3 H WJ-2 - Almost clean to the bare substrate; very thorough cleaning; randomly dispersed visible stains of previously existing rust, paint, and foreign matter is allowed on only 5% of the surface

WJ-3 - Thorough cleaning; randomly dispersed visible stains of previously existing rust, paint, and foreign matter isallowed on only one-third of the surface


removed by a scraper. Water cleaning or ice blastingmethods increase the volume of waste due to the additionof the water. Even for the removal of non-lead containingcoatings, the resulting waste stream may be classified ashazardous due to either the caustic or the solvent compo-nent. Information on chemical stripping can be found in thetechnology update SSPC-TU 6, “Chemical Stripping ofOrganic Coatings from Steel Structures.”

9.2 SODIUM BICARBONATE BLASTING: A relativelynew, low dusting method of blast cleaning uses a slurry ofwater and sodium bicarbonate, a water soluble non-reac-tive salt, to remove paint from a surface. The portable unitcan be wheeled from one location to another. Once in place,the system requires a source of compressed air (typically600-700 kPa [85-100 psi] at the nozzle), clean water, anddrainage. In most cases, special ventilation or dust collec-tion is unnecessary. The operator can vary the angle ofattack, standoff, and dwell time to strip layer by layer or allat once.

This blast media is a formulation of sodium bicarbonateand is free from silica dusts and toxic fumes. The media isclaimed to be effective in:

• removing surface rust from screws and othermetal parts without imbedding itself into thematerial being stripped

• removing coatings down to the metal or onelayer at a time

• controlling layer removal, allowing for an extrameasure of safety when used on galvanized orother specialty protected metals

• removing grease, oil, paint, and dirt from flat orcontoured surfaces, cooling towers, motor parts,and hard-to-reach equipment parts.

This system was developed for removal of aircraftcoatings and similar materials from surfaces which do notrequire “profiling”. It also reduces dusting.

For blasting alone, productivity depends on the coatingbeing removed and the degree of cleaning. Removal ratescan be as high as 11 m2/h (120 ft2/h) for removal of thindeteriorated films. Removal of deteriorated thicker filmsmay be much slower, on the order of 2 to 5 m2/h (20 to 50ft2/h). Intact films may not be dislodged using sodiumbicarbonate blasting.

9.3 SPONGE JETTING: Another low dusting methodof cleaning, sponge jetting, involves the use of specializedblasting equipment that propels a manufactured urethanesponge against the surface to be cleaned. The spongeparticles are approximately 3 to 6 mm (1/8 to 1/4 inch) indiameter and are available in a mild grade for degreasingand aggressive grades for paint or mill scale removal. Theaggressive grades have the sponge formed around an

3

abrasive. Abrasives include staurolite, garnet, and steelgrit.

The productivity is lower than traditional abrasive blastcleaning (30-50% of the productivity), but typically will behigher than power tool cleaning to bare metal and vacuumblast cleaning. White metal quality of preparation is pos-sible and a surface profile of approximately 50 micrometers(2 mils) can be achieved. The dust generated is low be-cause the cells of the sponge help to suppress the dust, andthe paint tends to be dislodged in larger chips rather thanbeing pulverized, as is the case with traditional abrasiveblast cleaning.

9.4 CARBON DIOXIDE (DRY ICE) BLASTING: In thisdust free method, liquid carbon dioxide is formed intopellets of dry ice using specialized equipment. The CO

2

pellets are approximately the size of rice. The pellets areconveyed through a blast hose using compressed air in amanner similar to open abrasive blast cleaning. The pelletsexit through a specialized nozzle assembly.

An advantage of CO2 blasting is a reduction in thevolume of debris created as the abrasive sublimes uponuse. As a result, the waste involves only the paint beingremoved. Carbon dioxide is also non-conductive and willnot create a spark, and therefore can be considered for usein areas where any sparking is unacceptable.

Disadvantages are that the abrasive does not appearto be hard enough to productively remove heavy coatings,rust, or mill scale. More than just stains of old primer willremain on the surface. Tight coatings are difficult to removewithout frosting the surface. The equipment is also expen-sive.

9.5 ELECTROCHEMICAL STRIPPING: A very recentmethod of paint removal is electrochemical stripping. Byapplying cathodic current to a painted metal substrate,disbonding of the coating is achieved. The benign electro-lyte is contained in a liquid-absorbent material to which acounter electrode is attached. This combination, often com-bined with a liner, is applied to the painted metal surface,with magnets in the case of steel. If the paint is intact it mustbe scored to initiate current flow. After electrochemicaltreatment for 0.5 to 2 hours at 8 to 10 volts, the pads areremoved and paint fragments are recovered. No particlesbecome airborne making this method attractive for leadpaint removal.

Banks of conducting pads may cover an area up to 14m2 (150 ft2) and can be run simultaneously. This methodwas developed particularly for application on highway struc-tures to remove lead based alkyd-type coatings, but it maybe employed for paint removal on other objects.

10. Film Thickness

It is essential that ample coating be applied after blast

1


cleaning to adequately cover and protect the peaks of thesurface profile. The method of measuring dry film thickness(DFT) described in SSPC-PA 2, “Measurement of DryCoating Thickness with Magnetic Gages,” takes into ac-count the effect of surface profile so that the measured DFTis approximately the thickness of the coating over thepeaks. Thus, the depth of the surface profile should beconsidered in determining the amount of coating to beapplied. For example, if a 50 micrometer (two mil) DFT isdesired, it will require a larger volume of paint to fill thevalleys in a 75 micrometer (three mil) profile than to fill thevalleys in a 25 micrometer (one mil) profile and still have 50micrometers (two mils) over the peaks. Because of theexistence of rogue peaks, a greater coating thickness mayneed to be specified when coating deeper profiles.

11. Visual Standards

Note that visual standards, when used in conjunctionwith SSPC specifications, give only an approximation of thefinal surface condition, because the visual standards are

based on one specific set of steel conditions and cleaningoperations. These conditions will not be identical to theconditions faced on other projects. It is cautioned, there-fore, that any visual standards should be considered asupplement to, and not a substitute for, surface preparationspecifications. The use of the visual standards in conjunc-tion with SSPC specifications is required only when theyare specified in the procurement document covering thework. It is suggested, however, that the visual standards bespecified in the procurement document. Although they willnot precisely match the appearance of the steel on everyproject, they are a valuable aid in establishing the generalappearance described by the surface preparation specifi-cations, and are especially useful in depicting the relativedifferences between the various grades. Even when visualstandards are included in the procurement document, how-ever, it must be recognized that the written standardsprevail.

SSPC has visual standards for degrees of blast clean-ing (SSPC-VIS 1), for the amount of rust on a paintedsurface (SSPC-VIS 2), for hand and power tool cleaning(SSPC-VIS 3), and for water jetting (SSPC-VIS 4). SSPCcommittees are currently preparing a visual standard forwet abrasive blasting. Other associations, such as ISO, aswell as individual companies, have visual standards. Thefollowing sections summarize the SSPC visual standards.

11.1 SSPC-VIS 1-89,”VISUAL STANDARD FORABRASIVE BLAST CLEANED STEEL”: SSPC-VIS 1-89provides standard reference photographs for four rust grades(preblast conditions) and four degrees of blast cleaningthoroughness when using silica sand as the abrasive.SSPC-SP 5, 6, 7, and 10 are depicted over each initialcondition. SSPC-VIS 1-89 is a separate publication; how-ever, a written “Guide to SSPC-VIS 1-89” is included in this

32

volume. The appendix of SSPC-VIS 1-89 includes supple-mentary photographs depicting the appearance of whitemetal surfaces prepared from alternative non-metallic andmetallic abrasives.

11.2 SSPC-VIS 2, “STANDARD METHOD OF EVALU-ATING DEGREE OF RUSTING ON PAINTED STEEL SUR-FACES”: This standard defines a rust grade scale whichgoes from 10 (no rust) to 0 (totally rusted). The 2000 editionof SSPC-VIS 2 defines three rust distributions:

• General Rust – consisting of various size rustspots randomly scattered over the surface

• Spot Rust – where the rusting is concentrated ina few large spots

• Pinpoint Rust – where each rust spot is verysmall and scattered across the surface.

This visual standard consists of 27 color photographsdepicting rust grades 1 to 9 for each rust distribution. Thephotographs were computer enhanced to show the exactpercentage of rust defined in the written standard. For eachcolor photograph, there is a corresponding black and whiteimage showing only the rusted areas. The previous editionof SSPC-VIS 2 had been jointly adopted by the AmericanSociety of Testing and Materials as ASTM D 610. The setof 27 color photographs that show rust staining and repre-sent a more realistic picture of the painted surface isavailable from SSPC as a separate document. The writtendescription and the black and white images are containedin this volume.

11.3 SSPC-VIS 3, “VISUAL STANDARD FOR POWER-AND HAND-TOOL CLEANED STEEL”: This standard pro-vides color photographs for the various grades of hand andpower tool cleaning (SSPC-SP 2, 3, and 11) for variousinitial conditions of the steel. Seven initial conditions aredepicted (four rust grades and three painted surfaces).While a guide to the standard is included in this volume, thephotographs are only available as a separate supplement.

Written specifications are the primary means to deter-mine conformance with cleaning requirements; photographsshould not be used as a substitute for the written specifica-tions.

11.4 SSPC-VIS 4/NACE No. 7, “INTERIM GUIDEAND VISUAL REFERENCE PHOTOGRAPHS FOR STEELCLEANED BY WATER JETTING”: This guide depicts twoinitial rust grade conditions cleaned to two degrees of waterjetting cleanliness (SSPC-SP 12 conditions WJ-2 and WJ-3), each with three levels of flash rusting after cleaning.Table 7 gives the matrix identifying each picture.

11.5 ISO VISUAL STANDARDS: The InternationalOrganization for Standardization (ISO) in conjunction withSwedish Standards Institution (SIS) has issued a booklet of


photographs (ISO 8501-1:1988/SIS SS 05 59 00) depictingthe appearance of surfaces prepared by hand and powertool cleaning, abrasive blast cleaning (four degrees) andflame cleaning. The methods of cleaning are depicted overvarious rust grades of unpainted steel. ISO 8501-2 depictsa similar set of surfaces where the substrate was previouslypainted steel.

11.6 OTHER PHOTOGRAPHIC STANDARDS: TheProduction Technical Society (Japan) has printed colorillustrations of wash primed and zinc-rich primed steelbefore and after weathering and re-cleaning. The photo-graphs of the Shipbuilding Association of Japan illustratethe appearance of painted, unpainted, welded, and flame-cut steel before and after various degrees of damage orweathering.

British standard BS 7079 Part A1 is equivalent to ISO8501-1 (unpainted steel) and BS 7079 Part A2 is equivalentto ISO 8501-2 (previously painted steel).

NACE International had previously developed visualaids for evaluating the degree of cleanliness of blast cleanedsteel (TM-01-70 and TM-01-75), but they were withdrawn in1995. Visual standard NACE No. 7 is jointly issued asSSPC-VIS 4 described above.

11.7 PROJECT PREPARED STANDARDS: Preparedsteel will often appear differently from the photographicstandards due to variations in initial surface conditions,abrasives being used, and so forth. Because of difficultiesin comparisons, it is sometimes recommended that thecontractor prepare blast cleaned samples representative ofthe steel to be blasted which, by mutual agreement of theowner and the contractor, are representative of the requiredsurface cleanliness and appearance. Suggested dimen-sions of the reference steel panels are approximately 15 x15 x 0.5 cm (6 x 6 x 3/16 inch) minimum. The blast cleanedpanels should be completely protected from corrosion andcontamination, and maintained as visual reference stan-dards for the duration of the project. As an alternative to testpanels, portions of the structure being prepared can beused.

12. Other SSPC Surface Preparation Documentsin This Volume

12.1 SSPC-TR 1/NACE 6G194, “JOINT TECHNOL-OGY REPORT ON THERMAL PRECLEANING”: Thermalprecleaning is used in conjunction with other surfacepreparation methods, such as abrasive blast cleaning, to

remove soluble salts from the pits of heavily corroded steel.The oil and gas industry as well as the rail car industry usethermal precleaning extensively. This report describes theparameters used for dry heat and wet heat. It also listsmethods for verifying the surface cleanliness.

12.2 SSPC-TR 2/NACE 6G198, “JOINT TECHNICALREPORT ON WET ABRASIVE BLAST CLEANING”: Thisdocument covers procedures, equipment, and materialsinvolved in a variety of air/water/abrasive, water/abrasive,and water-pressurized abrasive blast cleaning systems.Various types of wet blast systems are described andcompared. SSPC-TR 2 discusses selection of abrasives,water delivery systems, inhibitors, and equipment opera-tion and maintenance. (See Section 7.2.)

12.3 SSPC-TU 2/NACE 6G197, “INFORMATIONALREPORT AND TECHNOLOGY UPDATE: DESIGN, IN-STALLATION, AND MAINTENANCE OF COATING SYS-TEMS FOR CONCRETE USED IN SECONDARY CON-TAINMENT”: This state-of-the-art report covers the de-sign, installation, and maintenance of polymeric coatingsystems that are applied and directly bonded to concrete issecondary containment applications. This report is intendedto inform manufacturers, specifiers, applicators, and facilityowners who are required to contain chemicals and/or pro-tect concrete in these applications.

A chemical resistant coating is often applied to con-crete to extend the service life of the secondary contain-ment structure and properly contain the chemicals. Thisreport focuses on those aspects of the design, materials,and procedures that are specific to coating for concrete insecondary containment applications, making reference toother publications when appropriate. While there are nu-merous successful commercial products and designs forcontainment of chemicals, this report focuses on concretestructures that are coated with thermoset polymer coatingsystems. Other potentially effective containment systems,such as acid-resistant brick and thermoplastic liners, arenot described in this report.

12.4 SSPC-TU 4, “FIELD METHODS FOR RETRIEVALAND ANALYSIS OF SOLUBLE SALTS ON SUB-STRATES”: This technology update describes methods forestimating the amount of soluble salt on a surface. Twotypes of retrieval methods, the cell method and the swab-bing or washing method, are applicable to field retrieval.The “total” extraction method involves immersion of thesurface in boiling water and, hence, is useful only in alaboratory.

SSPC-TU 4 gives detailed procedures for obtaining aliquid sample and for analyzing it to determine the level ofsoluble salt. Test kits are available to simplify the extractionand analysis. The SSPC standard on water jetting, SSPC-SP 12, defines three levels of soluble salt contamination ornon-visible surface cleanliness.

12.5 SSPC-TU 6, “CHEMICAL STRIPPING OF OR-GANIC COATINGS FROM STEEL STRUCTURES”: Thisdocument defines chemical strippers and discusses their

33


use for removing conventional organic coatings from steelstructures. Chemical stripping involves application of achemical to existing paint, allowing it to dwell for a period oftime to attack the organic binder, removing bulk paint/stripper residues, and properly cleaning the steel substrateprior to repainting. This technology update describes meth-ods used to identify the type of stripper that will work mosteffectively, and typical application and removal options. Italso presents containment and disposal options for stripperwastes.

13. Non-SSPC Cleaning Specifications

The recommendations, specifications, and guides of anumber of other associations reference the SSPC surfacepreparation specifications, including: American Associa-tion of State Highway and Transportation Officials(AASHTO); American Institute of Steel Construction (AISC);American Iron and Steel Institute (AISI); American Petro-leum Institute (API); American Railway Bridge and BuildingAssociation (ARBBA); American Water Works Association(AWWA); Canadian Institute of Steel Construction (CISC);Painting and Decorating Contractors of America (PDCA);Steel Plate Fabricators Association (SPFA); and the TexasStructural Steel Institute (TSSI). They are also used bymany state highway departments and other federal, state,and local agencies.

Governmental agencies have been active in preparinggood surface preparation specifications, but most of thesedeal with thin metal and do not particularly apply to struc-tures. The US Army Corps of Engineers Civil Works Divi-sion has issued CW-09940, “Guide Specifications for Paint-ing Hydraulic Structures and Appurtenant Works.” Thisspecification covers the cleaning and treating of structuralsteel as well as the application of paint and the paints to beused. It makes use of the SSPC surface preparation speci-fications.

Federal Specification TT-C-490, “Cleaning Methodsand Pretreatment of Ferrous Surfaces for Organic Coat-ings,” covers various types of surface preparation andpretreatments.

For internal use, the U.S. Department of the Navy,Naval Sea Systems Command, has prepared Chapter 631,“Preservation of Ships in Service (Surface Preparation andPainting) NAVSEA-S9086-VD-STM-OOOC/H-631,” whichincludes surface preparation specifications in addition topainting specifications and paint systems. Detailed specifi-cations for pickling are included.

The International Organization for Standardization (ISO)has included written definitions and photographs depicting

34

the appearance of uncoated steel surfaces cleaned byflame cleaning (ISO 8501-1: 1988). This book also includesphotographs for uncoated steel surfaces cleaned by handand power tools and by abrasive blasting. A parallel stan-dard ISO 8501-2 depicts degrees of cleaning over previ-ously painted surfaces.

The British Standards Institution standard BS7079:Parts A1 and A2, “Preparation of Steel SubstratesBefore Application of Paints and Related Products” is es-sentially equivalent to ISO 8501-1 and ISO 8501-2.

14. Surface Preparation of Concrete for Coating

14.1 INDUSTRY STANDARDS: There are several rela-tively new SSPC publications for surface preparation andcoating of concrete included in this volume:

• SSPC-SP 13/NACE NO. 6, “Surface Preparationof Concrete”

• SSPC-TU 2/NACE 6G197, “Informational Reportand Technology Update: Design, Installation,and Maintenance of Coating Systems forConcrete Used in Secondary Containment”

• SSPC-Guide 11, “Guide for Coating Concrete.”

The International Concrete Repair Institute (ICRI) hasdefined nine concrete profiles, thirteen methods of achiev-ing them, and five different coating thickness ranges. ICRIhas also developed a set of rubber replica specimens forthe nine different profiles. These rubber replicas and theaccompanying document, ICRI Guideline No. 03732, “Se-lecting and Specifying Concrete Surface Preparation forSealers, Coatings, and Polymer Overlays,” are availablefrom SSPC. NACE and ASTM have also issued standardson surface preparation, repair, coating, and inspection ofconcrete. These are referenced in the SSPC documentslisted above.

14.2 METHODS OF CLEANING CONCRETE: Con-crete may be cleaned by many of the same methods usedto clean steel for painting. However, care must be exercisedso as not to damage the concrete surface. Concrete may becleaned with detergent/power washing, alkaline or steamcleaning, chemical cleaning, abrasive blasting, high-pres-sure water cleaning, or mechanical cleaning with pneu-matic tools, scarifiers, and scabblers. Efflorescence mustbe removed from cementitious surfaces by dry wire brush-ing or other mechanical means before any washing occurs.Water will merely dissolve the efflorescence and force itinto the concrete.

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Documents

sspc specifications

sspcsp com

sspc publication

cleaning of steel

water cleaning

wet abrasive blast cleaning

blast cleaning parameters

cleaning methods