CSIRO5

CSIRO2

National Building Technology Centre

Bulletin 5

EARTH-WALL CONSTRUCTION

FOURTH EDITION

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NATIONAL BUILDING TECHNOLOGY CENTREP.O. BOX 30 CHATSWOOD 2057FAX: 888 9335TELEX: AA123400PHONE: 888 8888

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CSIRO2

National Building Technology Centre

Bulletin 5

Earth-Wall Construction

FOURTH EDITIONG.F. MiddletonRevised by L.M. Schneider1987

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First published 1952Second edition 1976Reprinted 1980Third edition 1981Republished 1982Republished 1983Fourth edition 1987

ISBN 0 642 12289 X

Commonwealth of AustraliaDepartment of Industry, Technology and Commerce

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CONTENTS

Introduction

Section 1 Scope and General1.1 Scope1.2 Site selection1.3 Orientation for solar design1.4 Footings1.5 Damp-proof course1.6 Lintels1.7 Holding-down bolts and top plate1.8 Chimneys and fireplaces1.9 Fixing of doors and windows1.10 Wet areas1.11 Fixing to walls1.12 Coatings1.13 Installation of services1.14 Garden walls and boundary fences1.15 Reinforcement1.16 Cyclone-resistant construction1.17 Earthquake-resistant construction1.18 Frame construction1.19 Protected walls

Section 2 Selection of Soil

2.1 The nature of soil2.2 Artificial soils2.3 Soil stabilisation2.3.1 General2.3.2 Clay stabilisation2.3.3 Cement stabilisation2.3.4 Bituminous stabilisation2.3.5 Lime stabilisation2.3.6 Chemical stabilisation2.4 Assessment of soils2.4.1 General2.4.2 Soils for mud brick (adobe)2.4.3 Soils for rammed-earth (pise)2.4.4 Soils for machine made blocks2.4.4.1 Cement-stabilised pressed blocks2.4.4.2 Unstabilised pressed blocks2.5 Dimensional consistency

Section 3 Design Criteria

3.1 General3.2 Durability3.3 Structural properties3.3.1 Structural values3.3.2 Distance between openings3.3.3 Design for wind loading3.4 Fire resistance3.4.1 Fire rating3.4.2 Combustibility3.5 Air-borne sound transmission3.6 Thermal properties3.6.1 Insulation3.6.2 Thermal mass

Section 4 Rammed-Earth (Pise) Construction4.1 Preparation of soil4.2 Formwork4.3 Compaction4.4 General considerations4.5 Holding-down bolts

Section 5 Mud Brick (Adobe) Construction5.1 Preparation of soil5.2 Moulding blocks5.3 Laying blocks5.4 Holding-down bolts

Section 6 Pressed Soil Block Construction

6.1 Cinva-ram construction6.1.1 Preparation of soil6.1.2 Moulding of blocks6.1.3 Mortar6.1.4 Wall construction6.2 Mechanically pressed-soil block

construction6.2.1 Block-making machines6.2.2 Preparation of the soil6.2.3 Moulding of blocks6.2.4 Mortar6.2.5 Wall construction6.2.6 Holding-down bolts

Appendix

A Method of determining the necessary depth ofembedment at holding-down bolts

B The composition and method of application ofcement-render coats to earth-wall construction

C Bituminous stabilisation of soils

D Accelerated erosion test

E Method for determination of compressivestrength

F Metricated summary of Table 10 from reportBMS 78 Structural, heat transfer and waterpermeability properties of five earth-wallconstructions, National Bureau of Standards,U.S. Department of Commerce, 1941.

G Determination of density of rammed earth

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Cover Photo: Holiday units on Kangaroo Island Courtesy of Terrastone Pty. Ltd.

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Introduction

This publication first appeared as theCommonwealth Experimental Building StationsBulletin 5, Earth-wall Construction by G.F.Middleton (1952).

With metrication of the building industry inAustralia in the 70s a second metricated edition wasproduced in 1976. This second edition containedsome minor editorial changes but no change to thetechnical content other than metrication.

The revival of interest in earth-wall construction thatresulted from the energy crisis of the 70s, thegrowing environmental consciousness and the highcost of borrowing money highlighted the inadequacyof the information in this 2nd edition and thedecision was taken to revise it.

The third edition which was published in May 1981set out evaluation procedures for the mud-brick(adobe) rammed-earth (pise) and Cinva-ram methodsof construction and these procedures were generallyaccepted by Local Government for approval of theconstruction methods.

The Cinva-ram was the only pressed-block machinementioned in the third edition as it was the onlymachine in common use at the time. Mechanicalpresses had been used in the 60s, notably by theNorthern Territory Housing Commission, but theiruse had been discontinued. The Cinva-ram wasdeveloped in Bogota, Columbia, in the early 50s.However, it was not until the mid 70s that the firstmachines, made under licence in New Zealand, wereimported into Australia.

Very significant developments have taken place inearth-wall construction since the third edition waspublished and this fourth edition attempts to takecognisance of these developments and to provideguidance for the industry in the future. The mostimportant of these developments and thecorresponding guidelines are as follows:

while earth-wall construction is generallyaccepted by all levels of government inAustralia some councils still have reservationsabout its durability and structural adequacy andinsist on excessively wide eaves or verandahsand post and beam construction. Sections 3.2and 3.3 should dispel any such doubts.

as stated above, when the third edition waspublished in 1981 the Cinva-ram was the onlypressed-block machine in common use. Avariety of machines are available now andpressed blocks are being producedcommercially in quite significant numbers.Section 6 has been expanded to describe thetypes of machines available and appropriatequality requirements are specified in Section 2.

where other more complete information isavailable and should be used that information isreferred to and the inadequate information inthe third edition has been deleted from thisedition. For example footings for houses shouldbe designed in accordance with AS 2870 usingthe equivalencies given in Table 1.1. Similarlyno attempt has been made to cover solar,earthquake or cyclone design.

The provisions of this Bulletin are of necessitygeneralised and possibly conservative. They shouldnot therefore preclude the use of more specificinformation or more refined design by appropriatelyqualified and experienced persons. Nor are theyintended to inhibit the development of new methodsof construction.

Finally the assistance of Professor Alan Rodger,University of Melbourne, Messrs David Baggs, IanFactor, David Oliver, Brian Woodward and PeterYttrup who reviewed the manuscript and offeredmany constructive comments, and the manyearth-wall builders who have provided information(often without knowing it) is gratefullyacknowledged.

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SECTION 1

SCOPE AND GENERAL1.1 Scope1.2 Site selection1.3 Orientation for solar design1.4 Footings1.5 Damp-proof course1.6 Lintels1.7 Holding-down bolts and top plate1.8 Chimneys and fireplaces1.9 Fixing of doors and windows1.10 Wet areas1.11 Fixing to walls1.12 Coatings1.13 Installation of services1.14 Garden walls and boundary fences1.15 Reinforcement1.16 Cyclone-resistant construction1.17 Earthquake-resistant construction1.18 Frame construction1.19 Protected walls

1.1 Scope

This Bulletin sets out the requirements andcapabilities of the pise (rammed earth), adobe (mudbrick) and pressed-soil block methods of earth-wallconstruction for specifically Australian conditions.

Subject to compliance with these requirements andcapabilities the methods of construction can be usedfor any of the classes of building defined in Part A3of the Building Code of Australia (1986 Draft).

1.2 Site selection

Because of its vulnerability to prolonged contactwith water, earth-wall construction should not beused on a site that is subject to flooding. If there isany possibility of this, the soil should becement-stabilised as a precaution. General siteconsiderations are shown in Fig. 1.1.

1.3 Orientation for passive solar heating

Earth-wall being a high mass type of construction,has the capacity to be utilised to provide bothwarmth and coolness.

To do this the building must be correctly designed,built and managed.

For passive solar heating, orientation of glass areasto the north is essential, the ideal orientation beingwithin 10 degrees of true north.

Solar design is a complex subject and is outside thescope of this Bulletin.

Fig. 1.1-Typical site conditions

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1.4 Footings

Footings for earth-wall for one and two storeyresidential buildings should comply with therequirements of Australian Standard 2870-Residential Slabs and Footings, using theequivalencies set out in Table 1.1.

The footings for non-residential buildings should bedesigned in accordance with the relevant engineeringprinciples.

Table 1.1 Construction equivalencies forfooting design to AS 2870

Earth-wall Construction Equivalent construction inAS 2870

Post and beam with infill earthwalls (stabilised orunstabilised)

Articulated masonry veneer

Load-bearing unstabilisedearth walls with or withoutarticulated joints

Articulated full masonry

Load-bearing cementstabilised earth walls witharticulated joints

Articulated full masonry

Load-bearing cementstabilised earth walls withoutarticulated joints

Full masonry

Note: For the purpose of this table soils stabilised withclay, bitumen, lime and chemicals are considered tobe unstabilised.

1.5 Damp-proof course (dpc)

Any of the damp-proof course materials normallyaccepted under building regulations is suitable foruse with earth-wall construction with the exceptionof the damp-proof mortars allowed in some States.The best materials are those that remain flexible andtherefore are unlikely to fracture due to shrinkage inthe wall or minor foundation movement. Suchmaterials include the lead, copper andaluminium-cored bituminous damp-proof courses.

A damp-proof course should be placed at the base ofall earth walls even though a moisture barrier hasbeen placed under a slab-on-ground type footing.

To avoid damage by flooding of slabs duringconstruction and by accident in wet areas earth wallsshould be set on a concrete plinth as shown inFig. 1.3, on a course of burnt clay bricks or cementblocks.

If the wall is to be placed directly on a slab, the dpcshould be upturned and then protected and concealedby a skirting and downturned at least 25 mm at theslab edge as shown in Fig. 1.2.

Fig. 1.2 Detailing of damp-proof course whenearth wall is placed directly onconcrete slab.

1.6 Lintels

Any structurally adequate form of lintel can be used.Lintels must be as wide as the earth wall theysupport. There should be sufficient length to give abearing surface at least 225 mm each side of theopening. The whole structure can be strengthened bykeeping the window and door heads at the samelevel and constructing a continuous reinforcedconcrete lintel completely around the building.Under normal conditions, this precaution is notessential.

1.7 Holding-down bolts and top plate

All forms of earth-wall construction can support notonly conventional roofing systems but also heavytypes, such as sod roofs. With low-pitched metalroofs, concern is not just with support but anchoringthem against uplift.

In cyclone-prone areas, cyclone bolts are mandatory,(see Fig. 1.3). In other areas consideration must begiven as to whether a sufficient weight of wall isbeing harnessed to resist the uplift forces.

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Appendix A outlines a procedure for determining thenecessary depth of embedment of holding-downbolts. The depth of embedment determined inaccordance with Appendix A must be increased byhalf as much again to ensure overall stability of thewall.

The top plate in earth-wall construction shoulddouble as a perimeter beam to increase the stabilityof the walls. In earthquake and cyclone-prone areasspecial precautions are necessary and these areoutlined in Section 3.

The top plate of timber 200 mm 50 mm is beddedon a levelling course of mortar and secured to thewall by either bolts or galvanised steel straps. If

steel straps are used, they should be brought overthe top plate alternately in opposite directions.Details of methods of securing the top plate to thetop of the wall are shown in Fig. 1.4. Fig. 1.5 showsthe method illustrated in Fig. 1.4 (c) being used.

Above the top plate, the roof construction is thesame as for any other form of masonry building.Care must be taken to ensure that the walls are notsubject to lateral loading; raking purlin struts mustbe kept in the plane of the wall supporting them.

Some details of the installation of roof anchoringsystems for the different types of construction aregiven in sections 4, 5 and 6.

Fig. 1.3 Installation of cyclone bolts in adobe walls.

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Fig. 1.4 - Methods of securing the top plate

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Fig. 1.5 Top plate holding-down bolts being built into an adobe wall

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1.8 Chimneys and fireplaces

Brick or stone chimneys are recommended with therequired opening being left in the wall and thefireplace and chimney built in after the walls havebeen completed. Suitable ties, such as galvanisedsteel straps should be placed in the wall duringconstruction and the ends left projecting so that theycan be built into the fireplace masonry as the workproceeds. Fireplaces can be built using the differentearth-wall methods provided that the fireplace itselfis built with burnt clay bricks, a steel or fired brickflue lining is provided and the earth-wallconstruction above roof level is stabilised for addedweather resistance.

The construction of fireplaces is described in theNBTC Note on the Science of Building No. 31.

1.9 Fixing of doors and windows

The reveal of door and window openings may besquare or splayed. With pise construction thesplaying is formed by fillets fixed in the forms.Appropriately shaped adobe blocks are moulded asdescribed in c1.5.2 and illustrated in Fig.5.7. Thesplayed option is not available with pressed-blockconstruction.

Window and door frames may be set in place andthe walls built around them or they can be set inafter the wall is constructed. The method of fixingframes to jambs will depend upon the sequenceused. Some common methods of fixing are shown inFig. 1.6. Alternatively, continuous fixing strips canbe built into the wall as shown in Fig. 1.7. Thefixing strip itself is fixed into the wall by one of themethods shown in Fig. 1.6.

(a) T-nailing block

(b) Wedged nailing block

(c) G.I. face-fixed wall tie

(d) Fixing bracket for steel frames. For added stability and fireresistance frame is filled with mortar

Fig. 1.6Methods of fixing door and window frames to earth walls.Note locating nails in (a) and (b) and clouts in (c) and (d)

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(e) Adobe blocks with integral nailing blocks

(a) Strip being incorporated in rammed earth

(b) Mould for adobe blocks to accommodate fixing strip

Fig. 1.7 Continuous fixing strip

1.10 Wet areasEarth-wall can be used as the main wall constructionin wet areas except where water is likely to be incontact with it for sufficient time for the water to beabsorbed such as at the floor of a shower recess. Insuch areas earth wall should be protected by aprefabricated base or by a suitable durable waterproof membrane. Alternatively a completepre-fabricated shower recess could be installed.In less critical wet areas earth-wall should berendered and tiled or otherwise protected by awater-resistant coating. The base of walls must beprotected by a dpc as described in Par. 1.5.Figs. 1.8 and 1.9 show wet areas in existingbuildings.

1.11 Attaching fixtures to earth wallsProvided appropriate fastenings are used, earth wallsare capable of supporting the weight of pictures,kitchen cupboards and similar static loads.For light fixtures nails at least 50mm long can beused. For heavier fixtures longer nails or screws ofthe type used for fixing roof-sheeting are moresatisfactory. For the screws the wall should bepre-drilled with a masonry drill to half the finaldepth of the thread.Heavy vibrating machines such as clothes driersrequire special consideration.

1.12 CoatingsExternal walls that satisfy the requirements ofSection 2 do not need to be coated for protectionfrom erosion by the weather. Walls that do not meetthese requirements can be made weather-proof bythe application of a cement render coat or by theapplication of a chemical waterproofing agent.The use of cement render has been tried and provento be satisfactory over a period of many years. Thelong-term performance of chemical treatments is notknown except that they generally requirere-treatment at intervals of not more than 10 years.The application of cement render to pise walls anda method of forming the coating integrally with thewall are described in Appendix B.Internal walls should always be sealed to preventdusting and to facilitate cleaning.

1.13 Installation of servicesThe installation of plumbing and electrical servicesis the same as in other masonry construction exceptthat the absence of cavity walls may necessitate thecutting of chases. This can be minimised by layingelectric conduits and water pipes in the horizontaljoints in adobe and pressed block construction, andembedding them in rammed-earth walls as they arecompacted. Horizontal chases should not exceed50 mm in depth.

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Fig. 1.8 - Wet area showing render and tiling

Fig. 1.9 - Bathroom in pressed-soil brick home

Photo courtesy Sun Earth Homes

1.14 Garden walls and boundary fences

Garden walls and boundary fences can be built ofpise, adobe or pressed block and should be given thesame protection from moisture as the walls of abuilding, that is, a concrete base, damp-proof courseand a moisture-proof capping with sufficientoverhang on each side of the wall to throw offwater.

1.15 Reinforcement

Generally the reinforcement of buildings of one ortwo storeys is unnecessary because therecommended minimum thicknesses give adequatestrength to the walls.

1.16 Cyclone-resistant construction

In cyclone-prone areas earth-wall construction, aswith all other forms of construction must be built toresist extreme winds and torrential rain. In suchareas the wall material should have an erosion rateof not more than 0.25 mm/min when subjected tothe accelerated erosion test described inAppendix C. Few soils will meet this requirementwithout being stabilised.

In general the requirement is that there be continuityof strength from the footings to the roofing material.The earth walls have no tensile strength but they dohave considerable mass and this is harnessed bycyclone bolts which are anchored in the footings andpass vertically upwards through the walls and topplate which they hold in place as shown in Fig. 1.3.The nuts should be accessible so that they can betightened at least at the end of the first and secondsummers after construction.

However, there is much more than this tocyclone-resistant const ruct ion and theserequirements are set out in the building regulationsof Queensland and Western Australia and in theDarwin Area Building Manual.

1.17 Earthquake-resistant construction

In areas where there is a risk of earthquake themethod of construction of all forms of masonryincluding earth-wall must be such as to provideresistance to the lateral forces imposed by earthmovement.

Design for earthquake resistance is a specialistsubject and is outside the scope of this Bulletin.1.18 Frame construction

This form of construction consists of a frame oftimber or steel with adobe or pressed block infillpanels. Rammed-earth could be used but it would benecessary to leave the vertical timber postsfree-standing while the walls were being compactedbetween them. This would negate the mainadvantage of the method which is that the roof canbe built before the walls and so shelter the workarea.

The acceptance requirements for infill blocks is thesame as for those for load-bearing walls. Adequateprovision must be made for the transfer of thehorizontal stresses induced by wind or other lateralloading from the wall to the uprights and rackingloads from the uprights to the infill walls. Acommon problem with frame construction is thedifficulty of maintaining a seal between the timberframe and the infill earth walls.

Fig 1.10 and 1.11 show framed houses duringconstruction.

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Fig. 1.10 - Sawn-timber framed house under construction Courtesy Sun Earth Homes

Fig. 1.11 Sawn-timber framed house under construction

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1.19 Protected walls

Walls are considered to be fully protected fromerosion by the weather if the conditions shown inFig. 1.12 are satisfied. These conditions do notapply in cyclone-prone areas where all externalwalls are considered to be exposed irrespective ofwidth of eaves or verandah.

Note: For definition of terrain see AS 1170 The Wind Loading Code.

Fig. 1.12 Minimum eave or verandah width for walls to be considered to be protected from weather

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SECTION 2

SELECTION OF SOIL

2.1 The nature of soil2.2 Artificial soils2.3 Soil stabilisation2.3.1 General2.3.2 Clay stabilisation2.3.3 Cement stabilisation2.3.4 Bituminous stabilisation2.3.5 Lime stabilisation2.3.6 Chemical stabilisation2.4 Assessment of soils2.4.1 General2.4.2 Soils for mud brick (adobe)2.4.3 Soils for rammed earth (pise)2.4.4 Soils for machine made blocks2.4.4.1 Cement-stabilised pressed blocks2.4.4.2 Unstabilised pressed blocks2.5 Dimensional consistency

2.1 The Nature of the Soil

Soil is the term used to describe the material whichcovers most of the earths land masses. It is derivedfrom the breakdown of rock by weatheringprocesses. A soil may overlay the remains of therock from which it was formed or it may have beentransported by wind, water, glacial action and so onand then deposited in its present location.

Soils represent the end product of the weatheringprocess and are made up of chemically inertfragments. These fragments range in size fromcoarse gravel through fine gravel to sand, silt andfinally to clay. The particles sizes for each of thefractions as defined in Australian Standard 1289 aregiven in Table 2.1.

Not all soils are suitable for earth-wall construction.The problem is to determine by some form of quickassessment which soils are and which are notsuitable. In localities with a long history ofearth-wall construction, such as the Eltham area inVictoria such assessment would not be necessary.Similarly, the soil from the grounds of NBTC hasbeen used for experiments over many years and hasdemonstrated its suitability for adobe blocks.

In most areas of Australia, however, there is neithersuch prior knowledge nor have the people makingthe assessment had any previous experience withsuitable soils and definite guidelines are required.

Table 2.1 Particle sizes of different soil fractions

Gravel Coarse 60 mm - 20 mmMedium 20 mm - 6 mmFine 6 mm - 2 mm

Sand Coarse 2 mm - 600 umMedium 600 um - 200 umFine 200 um - 60 um

Silt Coarse 60 um - 20 umMedium 20 um - 6 umFine 6 um - 2 um

Clay The fraction of a soil composed ofparticles smaller in size than 2 um

The top layer of soil will normally contain a highproportion of vegetable matter in the form ofdecaying leaves, the roots of living plants and thelike. This layer is the topsoil in Fig. 2.1 and is notusually suitable for any form of earth-wallconstruction.

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Below the topsoil is the subsoil and its thickness andcomposition are determined by such variables as theorigin of the soil if transported, the type of rockfrom which it was derived if in-situ, the climaticconditions to which it has been subjected and itsperiod of formation.

Most subsoils consist of a range of particles fromfine sand to clay but the proportion of the differentfractions (the grading of the soil) can give the soilvastly different characteristics. Moreover, in thecase of the clay fraction the characteristics of thesoil depend not only on the amount of clay presentbut also on the type of clay. The assessment of soilsis discussed in more detail in Cl.2.4

Fig. 2.1 Profile of soil in-situ

2.2 Artificial Soils

In a world that is becoming increasingly consciousof the need to preserve the environment and toconserve energy every effort should be made toutilise waste products, especially as this will removethe need for the disposal of these products. Thedifferent methods of earth-wall construction lendthemselves very readily to the use of quarry wastesand other waste materials such as fly ash, minetailings, the washings from river gravel andsand-winning operations and so on.

Expert advice should be sought before suchmaterials are used, firstly to ensure that the mosteconomical but adequate blend of materials isdetermined and, secondly, because some minetailings contain hazardous materials that may requirespecial precautions in handling or might evenproduce construction that would be quite unsuitablefor human or other occupancy. Examples of thelatter would be tailings from asbestos mining andtailings containing cyanide or other toxic chemicalsthat were used in the separation process.

2.3 Soil Stabilisation

2.3.1 General

Soils that lack sufficient cohesion (normallyimparted by the clay content) must be stabilised toachieve the required cohesion.

Stabilising agents in normal use in Australia are:

clay cement bituminous emulsion lime chemicals

In other parts of the world and in former times inAustralia, materials such as cow-dung, rice husksand ant-beds are or were used for this purpose. Inthis publication, as has been mentioned previously,only materials and methods compatible with presentAustralian standards are considered.

In this section all percentages are by weight of drysoil. As a guide the percentages by volume can betaken as half these values as the density of cementis approximately twice that of soil.

2.3.2 Clay stabilisation

Clay stabilisation involves the mixing of a heavysoil with sand or a sand-silt soil. If the two types ofsoil are available the method appears attractive. Inpractice it is extremely labour intensive and shouldbe contemplated only where there is no practicablealternative and where abundant labour is available.

The mixing must be very thorough. This can beeffected in either the very wet or very dry state butit is difficult to get clay into either of these states.

If it is decided to mix the materials in the dry stateboth the sandy soil and the clay must be thoroughlydried. While the clay can still be cut fairly easily itshould be broken down into small clods and whenthese have dried they must be further crushed to afine powder. This fine clay and the sand are blendedin carefully controlled proportions and in quantitiessufficient to cast a trial block or trial section ofwall. From these trials the optimum blend can beselected on the bases of ease of handling and thequality of the finished product.

If the wet method is to be used the clay is placed ina hole or cut-down tank and water added andkneaded into it until it has the consistency of aslurry. This process may take several days. Theslurried clay and sandy soil are mixed, again in arange of proportions, and the resulting mixturesallowed to dry out if necessary before trial blocksare cast or sections of wall are rammed. Theoptimum mix is then selected according to the abovecriteria.

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2.3.3 Cement stabilisation

In earth-wall construction cement stabilisation isused for two purposes - firstly to provide cohesionin a low-cohesion soil and secondly to reduce theeffective clay content of a soil that would otherwisehave too high a clay content.

Soils lacking adequate cohesion are usually sandsilts and they are easily stabilised with relativelysmall amounts of cement. In addition, because thesesoils are usually free flowing, they can be mixedwith the cement in conventional concrete mixerswhich reduces the amount of work involved. Theamount of cement required is a function of thegrading and fineness of the soil particles. Arelatively coarse-grained well graded sand silt mayrequire as little as 2 1/2 per cent of cement while apoorly graded, fine-grained silt may require as muchas 10 per cent. Further, the amount of cementrequired varies with the method of earth-wallconstruction adopted. The higher the cement contentthe more prone the soil-cement mixture will be todevelop shrinkage cracks as concrete does. In themanufacturer of Cinva-ram or adobe blocks theshrinkage would not be a problem, but in pise wallsit would need to be minimised.

The use of cement stabilisation to reduce theeffective clay content of a soil should be consideredonly after thorough evaluation testing. For this formof stabilisation the cement content is higher, rangingfrom a minimum of 5 per cent to as much as 15 percent for full effectiveness.

2.3.4 Bituminous stabilisation

Bituminous stabilisation is little used in Australia.However, for the sake of completeness the sectionon stabilisation with bituminous emulsion containedin the original edition of this Bulletin is reproducedin Appendix C.

2.3.5 Lime stabilisation

Whether or not a soil is amenable to limestabilisation is dependent upon the type and amountof clay it contains and to determine this requiresconsiderable sophisticated testing. For this reasonand also because

the gain in strength is much slower with limethan with cement stabilisation, and

the cost of lime in Australia is virtually the sameas cement, this method of stabilisation has littleto recommend it.

There are two relatively rare situations in which theuse of lime is justified. The first is in remote areaswhere limestone is available for the local productionof lime and the only soil available needs to bestabilised and is amenable to lime stabilisation. Thesecond situation is where the only soil available isa clay which is too heavy for the production ofadobe blocks. In this case the influence of the claycontent of the soil can be reduced by treating thesoil with 2 to 3 per cent of lime for 2 to 3 days afterwhich it can be stabilised with 7 to 10 per cent ofcement for adobe block manufacture. Obviously thisis a very labour intensive and expensive process andwould only be used as a last resort.

2.3.6 Chemical stabilisation

Chemical stabilising agents are being developed foruse in road construction and they could well havepotential for earth-wall stabilisation. The distributorsof such materials will need to have them fullyevaluated and provide the necessary information fortheir proper use.

2.4 Assessment of Soils

2.4.1 General

While a well-graded soil, that is, one which hasparticles ranging from sand through fine sand andsilt to clay, will be a bonus for all forms ofearth-wall construction, the optimum clay content inthe soil is dependent upon the type of constructionand the type of clay mineral in the available soil.

Mud brick (Adobe) is the least restrictive with themajority of soils being suitable in their natural state.Those that have too little clay can be stabilised withcement to make them suitable. Those with very highclay content are the least suitable as treatment withlime and cement to make them suitable is a labourintensive and costly operation.

Rammed earth (Pise) is fairly limiting in the rangeof suitable soils. As the walls are constructed inlong sections the drying of clay could causeshrinkage cracking. However, the soil is compactedat a low moisture content so in practice soils havinga significant clay content can be used.

The soil suitable for pressed-soil blocks isdetermined by the machine being used andespecially the method of feeding the moulds. If themoulds are fed by gravity or screw auger afree-flowing sandy soil is essential. If the mould isfilled manually there is no restriction on the soil thatcan be used. In practice it will be found thatrelatively few soils are suited to the production ofsatisfactory pressed-soil blocks without some formof stabilisation.

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The Cinva-ram, while being manually fed, cannotuse a soil with a high clay content and achieve areasonable rate of production. With this machine theamount of soil placed in the mould is very criticaland getting the quantity right with clayey soils is tootime consuming.

The evaluation criteria for each of the methods ofconstruction are discussed in following clauses andare summarised in Table 2.2.

In the south west of the United States themanufacture of adobe blocks has been extensivelymechanised but the process still simulates manualmanufacture and would be subject to the sameevaluation criteria.

At least one manufacturer in Australia is producingextruded-soil blocks. It would seem appropriate totreat these as unstabilised pressed blocks.

Any other novel method of construction or blockproduction would need to be assessed as to the mostappropriate evaluation procedure.

2.4.2 Soils for mud brick (Adobe)A block is made form the chosen soil in accordancewith the casting procedure described in Section 4and allowed to dry for at least 28 days.

At the end of this drying period the block should:

1. be able to be handled without crumbling or beingeasily damaged, and

2. not have developed any crack longer than 75 mmand wider than 3 mm or deeper, irrespective oflength or width, than 10 mm.

For internal walls and protected exterior walls theseare the only criteria to be met.

For exposed external walls the following two furthercriteria must be met.

Subject a typical adobe block to theaccelerated-erosion test described in Appendix D.On completion of the test

3. the area subject to test shall not have, at anypoint, eroded at a rate faster than 1 mm/min., and

4. no water shall have penetrated the blockirrespective of the rate of erosion.

Table 2.2 - Evaluation Criteria

Evaluation procedure Test Limits

Type of Construction

Mud brick (Adobe) Rammed earth (Pise) Pressed blocksStabilised Unstabilised

Specimen preparation No damage whenhandled after drying

for 28 days

No significantcrumbling when form

is stripped

No damage whenhandled after curing

for 14 days

No damage whenhandled drying for 28

days

Visual inspection-cracking None longer than 75and wider than 3 ordeeper than 5 mm

As for mud brick As for mud brick As for mud brick

Dimensional Consistency - plan(max. variation from - heightnominal size-mm)

N/AN/A

N/AN/A

2.5 mm7.5 mm

2.5 mm7.5 mm

Accelerated erosion test (1)- Max. erosion rate (mm/min)- Water penetration

1Nil

1Nil

1Nil

1Nil

Adjusted Characteristic (2)Compression Strength (MPa) N/A 2(3) 2(4) 2(4)

(1) See Appendix D - 1 specimen required(2) See Appendix E(3) 3 specimens required(4) 5 specimens required.

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Criteria 1 and 3 are aimed at detecting soils that aredeficient in clay and hence are easily damaged anderoded, while criteria 2 and 4 are aimed at detectingsoils having too high a clay content and havedeveloped excessive cracking. Such cracking is notalways evident on the surface but nevertheless mayextend for almost the full thickness of the blocks.

2.4.3 Soils for rammed-earth (Pise)Soils most suitable for rammed-earth constructionhave a relatively low clay content and consequentlyhave little inherent erosion resistance.

In former times this was not a problem because itwas normal practice to render such construction andthe render provided the necessary protection fromthe weather.

Today it is more common to leave rammed-earthconstruction uncoated and the necessary resistanceto erosion by the weather is achieved by stabilisingthe soil. If the walls are to be left unprotected thefollowing evaluation procedure will determinewhether or not the walls will be satisfactory.

Compact a test specimen at least 800 mm long,300 mm high and 300 mm thick with thecompacting equipment to be used in the actualconstruction and with the soil at the optimummoisture content as described in Section 4. Thecompaction of a test specimen is illustrated inFig. 2.2.

Remove the mould immediately after completionof compaction and check that the soil shows nosign of crumbling. After drying for one monthcheck that it has not developed any visiblesurface cracks. If it is not intended to render orotherwise protect the wall from erosion orabrasion, subject the test specimen to theaccelerated-erosion test described in Appendix Dand ensure that it has an erosion rate not greaterthan 1.0 mm min and that moisture has notpenetrated to the other side of the specimenduring the test.

To ensure that a soil to be used for rammed-earthconstruction has adequate natural cohesion or can beadequately stabilised specimens prepared and testedin accordance with Appendix E must have anadjusted characteristic compressive strength of atleast 2 MPa.

Fig. 2.2 Preparat ion of rammed-earthspecimen for accelerated erosion test

(a) A mould for the preparation of rammed-earthspecimens

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(b) A rammed-earth test specimen being compacted

2.4.4 Soils for Machine Blocks

2.4.4.1 Cement-stabilised pressed blocks

Cement-stabilised machine-pressed soil blocks havebeen used extensively and have proved to be verydurable if correctly made.

The only quality control required for these blocks isthat sufficient cement has been used to adequatelybond the soil.

Inadequately stabilised soil will result in weak,easily damaged blocks.

The quality control criteria are

1. that the blocks not be able to be damagedmanually, and

2. that they pass the accelerated erosion test, and

3. that when tested in accordance with Appendix Ethey have an adjusted characteristic compressivestrength of not less than 2 MPa.

2.4.4.2 Unstabilised pressed blocks

Unstabilised pressed soil blocks have becomeavailable only very recently and hence there is nolong-term information on their performance.

The accelerated erosion test described inAppendix D will determine whether the blocks haveadequate clay content for erosion resistance andwhether or not they have cracked so as to allowwater penetration. However, this test is carried outwhen the blocks are only 28 days old and in the caseof these blocks they could change structurally overa period of years.

One possibility is that the clay in the blocks willtake in moisture and the blocks will disintegrate byswelling, and another that the clay will progressivelydry out and the blocks will develop the close patternof cracking characteristic of old china.

On the other hand neither of these possibilitiesmight eventuate and the blocks may give completelysatisfactory long-term performance.

In the absence of evidence to the contrary theaccelerated erosion test and a 2 MPa adjustedcharacteristic compressive strength requirement areconsidered the most appropriate evaluation criteriafor these blocks.

Should problems arise with blocks that have metthese requirements they are unlikely to endanger thestructural adequacy of the building.

2.5 Dimensional consistency

Pressed blocks are very regular in shape. Foracceptable appearance they should be laid with aregular bond and with horizontal and vertical jointsof reasonably uniform thickness. To make thispossible block dimensions must conform to thelimits given in Table 2.2.

The length and width of blocks are determined bythe mould dimensions and the variation in block sizeresults from drying shrinkage.

The block height depends upon the stroke of thecompressing ram which may be constant ordetermined by pressure. In the former machine blockdensity and in the latter block height will varydepending upon how uniform the mould feed is.Variation in density will be reflected in a highstandard deviation and hence lower characteristiccompressive strength determined in accordance withAppendix E.

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SECTION 3

DESIGN CRITERIA

3.1 General3.2 Durability3.3 Structural properties3.3.1 Structural values3.3.2 Distance between openings3.3.3 Design for wind loading3.4 Fire resistance3.4.1 Fire rating3.4.2 Combustibility3.5 Air-borne sound transmission3.6 Thermal properties3.6.1 Insulation3.6.2 Thermal mass

3.1 General

Earth-wall construction has its own uniquecharacteristics and it is inappropriate to applyquality control requirements or criteria applicable toother types of construction to it unless it can bedemonstrated that it is valid to do so.

The following sections contain such information asis available or can be conservatively assumed foruse in buildings of one or two storeys.

If it is proposed to use earth-wall for higher buildingor if refinement of design is desired appropriateadditional testing should be undertaken.

3.2 Durability

Earth-wall construction complying with therequirements of this Bulletin should have anunlimited life as it would be immune to thedestructive action of fire, termites and the weather.

As evidence of this durability Fig. 3.1 shows a pisehouse over 100 years old, Fig. 3.2 shows a sectionof Montsalvat, Eltham, built of adobe about 1940,and Figures 3.3 and 3.4 show buildings in Darwinbuilt of cement-stabilised pressed-earth bricks whichwithstood the onslaught of Cyclone Tracy in 1974.

As more direct examples Fig. 3.5 shows a stack ofadobe blocks in the NBTC grounds as originallystacked in 1981 and as they were in 1987; Fig. 3.6shows an adobe shed built by the author also in theNBTC grounds as it was in 1948 and again in 1987.

The only form of earth-wall construction beingconsidered in this Bulletin that does not currentlyhave a long performance history is thatincorporating unstabilised pressed blocks. Howeverthe indications are that such blocks meeting thequality control requirements described here willprove to be satisfactory.

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Fig. 3.1 A pise house over100 years old

Fig. 3.2 A s e c t i o n o fMontsalvat, builtof adobe about 1940

Fig. 3.3 A typical housebui l t by th eN o r t h e r nT e r r i t o r yH o u s i n gCommission fromstabi l i sed-earthbricks

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Fig. 3.4 A block of flats inDarwin built ofs t a b i l i s e d - e a r t hb r i c k s b y t h eNorthern TerritoryHousing Commission

Fig. 3.5

(a) Adobe blocks as stacked inNBTC grounds in 1981 toallow air circulation andfurther drying

(b) The same blocks as theyappear in 1987 after 6 yearsweathering

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Fig. 3.6

(a) Adobe shed in NBTCg r o u n d s s o o n a f t e rcompletion in 1948.

(b) The same shed as itappears today.

3.3 Structural properties

3.3.1 Structural values

Table 3.1 gives conservative structural values fordesign purposes if no testing is carried out andprocedures for arriving at more accurate valuesbased on test results.

A major investigation into the strength of earth-wallconstruction was carried out by the US Departmentof Commerce in 1941 and the results are reported inits report BMS 78. One shortcoming of thatinvestigation was that the same soil was used for allforms of construction and for some it wasinappropriate. Table 10 from that report isreproduced in Appendix F.

3.3.2 Distance between openings

The recommended minimum distance betweenopenings in earth-wall construction is dependentupon the wall thickness and is 1000 mm for 300 mmthick walls. For thicker walls this distance can bereduced by an amount equal to twice the additionalwall thickness. Thus, for walls 450 mm thick thedistance between openings should not be less than700 mm. The values for a range of wall thicknessesare given in Table 3.2. Shorter lengths than thosegiven in Table 3.2 can be used provided the wall isprotected from damage by impact and is notloadbearing.

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Table 3.1 - Structural values for earth-walldesign

Type of stress Safe design stress(kPa)No testing With testing

Compression 250 Cca*/5

Bearing (forbond beams,lintels and soon) 500 Cca/2.5Shear 10 + 10d where d is

depth below top ofwall (m).50 maximum

as for no testing

Tension in blocks 0 Average M.of R.of 5

blocks/10.50maximum

in joints 0 0Flexural

tensile 0 as above

compressive 750 Cca/1.7

* Adjusted characteristic compressive strength determined inaccordance with Appendix E.

Table 3.2 Recommended minimum distancebetween openings for different thicknesses of

wall

Wall thickness M i n i m u m d i s t a n c ebetween openings

(mm) (mm)250 1100300 1000350 900400 800450 700

Table 3.3 Regional wind speeds

City Regional wind speeds(m/s)

Adelaide 42Brisbane 50Canberra 38Darwin 55Hobart 41Melbourne 39Perth 40Sydney 44Townsville 55

3.3.3 Wind loading

Fig. 3.7 gives wall heights and spans for 40, 50 and60 m/s regional wind speeds. The regional wind

speeds for the eight capital cities and Townsville aregiven in Table 3.3 for a 50 year return period.

Walls may contain an opening not higher than H/2and not wider than H/3 provided the window jambsare well bonded to the wall.

For larger openings the jambs must be capable oftransferring the load on the window or door to acontinuous lintel or to the roof structure, and to thefloor structure.

The heights and spans for other wall thicknessesthan those given in Fig. 3.7 can be obtained bydirect interpolation.

The heights only can be increased by a factor of 1.3if the walls are subjected to a static load under allwind conditions of at least 2kN/m.

For two-storey construction where there is aperimeter beam or concrete slab at first-floor levelthe heights in Fig. 3.7 can be taken from the top ofthe beam or slab.

3.4 Fire resistance

3.4.1 Fire rating

NBTC has carried out a fire-resistance test on aload-bearing 250 mm thick adobe block wall. Theresult of the test was that the wall achieved afire-resistance rating of 4 hours in terms ofAS 1530, Part 4-1975. The test is reported fully inEBS Technical Record 490.

NBTC has also carried out a pilot fire test on a150 mm thick Cinva-ram block wall. This failed bypermitting excessive heating of the cold face at3 hours 41 minutes.

On this evidence all forms of earth-wall constructioncould be assumed to have a fire rating of 2 hours.

If fire ratings in excess of 2 hours are required thespecific type of construction should be tested.

3.4.2 Combustibility

Earth-wall construction is non-combustible.

An erroneous result can be obtained for thecombustibility test if the specimen is cut from ablock containing straw and straw is thereby exposed.Care must be taken to ensure that the surfaces of thespecimen tested are similar to those of the finishedwall.

3.5 Air-borne sound transmission

Limited testing indicates that 250 mm adobeconstruction with render on both sides can achievean air-borne sound transmission rating of 50 dbA.

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Fig. 3.7 Maximum height of wall (H) and spanbetween return walls (L) for 250, 300, 375 and450 mm wall thicknesses.

Wall Thicknessmm

Fig. Terrain CategoryMaximum values forwall height (H)and span (L)

Wall height (H)m

Span (L)m

Regional windspeed, m/s

Regional windspeed, m/s

40 50 60 40 50 60

a123

1.251.552.50

0.801.001.85

0.550.701.30

-

-

-

-

-

-

-

-

-

250 b 123

2.502.502.50

2.252.502.50

1.601.952.50

8.008.008.00

6.407.608.00

4.955.708.00

a123

1.501.853.00

0.951.202.20

0.650.851.55

-

-

-

-

-

-

-

-

-

300 b 123

3.003.003.00

2.703.003.00

1.902.353.00

9.009.009.00

7.008.359.00

5.456.279.00

a123

1.902.303.75

1.201.502.80

0.801.001.95

-

-

-

-

-

-

-

-

-

375 b 123

3.753.753.75

3.353.753.75

2.402.903.75

10.0010.0010.00

8.009.50

10.00

6.207.10

10.00

a123

2.252.804.50

1.451.803.30

1.001.252.35

-

-

-

-

-

-

-

-

-

450 b 123

4.504.504.50

4.054.504.50

2.903.504.50

11.0011.0011.00

8.8010.4511.00

6.807.85

11.00

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Thicker or more dense construction as would be thecase with rammed-earth and pressed blocks wouldachieve even higher ratings.

However, where such ratings are required theproposed construction would need to be tested.

3.6 Thermal properties

3.6.1 Insulation

The insulation properties of earth-wall are similar tothose of concrete or brickwork. Actual values aregiven in Table 3.4. Good insulation results from thegreater thickness of earth walls.

Table 3.4 Thermal Transmission of earth-wallconstruction

Wall thickness U-Valuemm W/M2C

250 2.86300 2.56350 2.33400 2.14450 1.97

3.6.2 Thermal mass

For passive solar heating the walls of buildings mustbe able to store heat during the day for re-radiationat night during the winter, or store night coolness tobe able to absorb heat from the air in the roomsduring the day in summer. This ability is known asthermal inertia and is due to a number of propertiesof the wall material which are collectively calledthermal mass.

Thermal mass is a characteristic of all forms ofheavy masonry construction and especially earthwall.

(PAGE 25 IN THE HARD COPY IS BLANK)

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SECTION 4

RAMMED-EARTH (PISE) CONSTRUCTION4.1 Preparation of soil4.2 Formwork4.3 Compaction4.4 General considerations4.5 Holding-down bolts

4.1 Preparation of soil

Soil at its natural moisture content is usually fairlyclose to the correct content for compaction. Whenthe soil is dug it should be covered to prevent itfrom drying out or becoming too wet. For every1 cubic metre of completed wall about 2 cubicmetres of loose soil or 1.5 cubic metres of in-situsoil will be required.

The soil must be compacted at the correct moisturecontent. This can be roughly determined by pressingthe soil into a ball in the hand as shown in Fig. 4.1(a) and dropping it from a height of 1100 mmFig. 4.1 (b).If it shatters into many small fragments the moisturecontent is correct Fig. 4.1 (c), but if it breaks intoonly a few large pieces Fig. 4.1 (d) it is too wet.Soil that is too dry cannot be formed into a ball.

This method of moisture determination is onlyapproximate because the actual moisture contentdepends upon the method of compaction. Fig. 4.2shows moisture plotted against density for twodifferent degrees of compaction. It will be seen thatthe greater the effort put into compaction the higherthe density of the compacted soil and the lower themoisture content required.

For a particular job the compactive effort to be usedand the soil will be constant and trials should bemade with soil slightly drier and slightly wetter thanthe content determined by the rough method justdescribed to determine the best moisture condition.If the soil is at the correct moisture content it willnot adhere to the rammer and after about 15 blowson each part of the area being compacted the soilwill give a ringing sound. If the soil is too dry itwill not compact but will shatter around the base ofthe rammer. Soil that is too wet will become spongyand when struck at one point will move nearby.

Layers of loose soil not more than 200 mm deepshould be used irrespective of the method oframming. If layers of greater depth are rammed thelower part of each layer will be insufficientlycompacted. Even with this thickness there is adifference in compaction throughout the layer.Fig. 4.3 shows how the more densely compactedupper part of each layer has resisted erosion moreeffectively than the lower part.

If the soil is to be cement-stabilised the cementshould be added and mixed into the soil and themixture brought to the correct moisture contentimmediately before the mixture is placed in theforms. Stabilised soil that has not been placed andcompacted within 1 hour of the cement being addedmust be discarded.

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(a)

(c)

(b)

(d)

Fig. 4.1 - Determination of the moisture content of soil by the drop test

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Fig. 4.2 - Relationship between compactive effort, moisture content and density of compacted soil

Fig. 4.3 - Different erosion of the top and bottom of layers of rammed earth

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4.2 Formwork

Formwork must be sufficiently robust to withstandthe pressure of the compacted soil.

Finished construction should conform to thefollowing tolerances:

Thickness 5 mm

Height 20 mm

From horizontal 10 mm in 4000

From vertical 10 mm in 3000

Fig. 4.4 illustrates a variety of types of formwork.However commercial construction companies havedeveloped much more efficient formwork systems.Fig. 4.5 shows some types of formwork in use.

Fig. 4.4 Illustrates a variety of types of formwork

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(c) ROLLER supported formwork used for the construction of straight walls and used inconjunction with the formwork illustrated in (d) and (e)

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(d) CORNER FORMWORK (e) PARTITION - WALL FORMWORK

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(a) Type 1 formwork

(b) Roller-supported formwork

(c) Formwork system developed by Terrastone Pty. Ltd.

Fig. 4.5-Rammed-earth formwork in use

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4.3 Compaction

Soil that contains any stone must be placed in theform without the stone separating out. This meansthat it cannot be dumped into the form by afront-end loader but must be shovelled from thebucket into the form. If the stone does separate outit is called segregation and the honeycombappearance produced is called boniness.

The thickness of layer to be compacted will bedetermined by the type of compacting equipmentbeing used but under no circumstance should theloose thickness be greater than200 mm.

The density of the wall should be 98 per cent ofstandard compaction determined in accordance withAustralian Standard 1289.E1.1. A method ofdetermining the density being achieved is describedin Appendix G.

Ramming may be manual or mechanical. Typicalrammers are shown in Fig. 4.6.

Fig. 4.6 - Examples of rammers (manual andmechanical)

4.4 General considerations

Soil that is overwet when placed in the forms shouldbe removed and returned to the stockpile. If it hasbeen cement stabilised it must be discarded.

Both faces of walls should be free from boninessdue to segregation. Small isolated areas may bepatched but walls showing segregation or inadequatecompaction over more than 5 per cent of their areashould be rejected.No through bolt should be loosened or disturbeduntil the full height of the section being compactedis completed. Through-bolt holes should be filledwith the same soil or soil/cement mixture being usedfor construction of the walls.

Cement stabilised walls should be cured for at least7 days by either keeping them moist by mistspraying with water as necessary or by wrapping inplastic. Fig. 4.7 shows the type of finish that can beachieved with off-the-form rammed-earthconstruction. Fig. 4.8 shows an owner-builtrammed-earth house in suburban Sydney, fig. 4.9shows a recently constructed rammed-earth churchat Margaret River, Western Australia, and fig. 4.10shows a six storey loadbearing rammed-earthbuilding in Weilburg, F.G.R., constructed in 1826.The walls of this building are 750 mm thick at thebase and decrease, presumably by 90 mm steps ateach floor level, to 300 mm at the top shown insection in fig. 4.11.

Assuming a density of 2,000 kg/m3 for the walls, afloor height of 3 m, a roof loading of 70 kg/m2, afloor loading of 2.0 kPa and a floor span of 6 m thestress at the base of the wall shown in fig. 4.11 is295 kPa, and on the bearing plates for the floorjoists is 67 kPa and the shearing stress induced bythe bearing plates is 48 kPa.

4.5 Holding-down bolts

Holding-down bolts must be placed in the wall so asto give the required embedment. Care must be takento ensure that they are not displaced by thecompacting operation.

If the rolling form shown in Fig. 4.4 (c) is beingused the holding-down bolts will need to besegmented to avoid being fouled by the yokes of theform.

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Fig. 4.7 -Interior wall of rammed earth

Photo courtesy Ramtec Pty. Ltd.

Fig. 4.8 -

Owner built rammed earth house

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Fig. 4.9 - St Thomas Catholic Church, Margaret River, WA. Photo Courtesy of Ramtec Pty Ltd, Cottesloe, W.A.

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Fig. 4.10 - A six storey loadbearing rammed-earth building at Weilburg, F.G.R. constructed in 1826

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SECTION 5MUD BRICK (ADOBE) CONSTRUCTION5.1 Preparation of soil5.2 Moulding blocks5.3 Laying blocks5.4 Holding-down bolts

5.1 Preparation of soilSoil is at the correct moisture content for mouldingadobe blocks when it no longer adheres to metalutensils or, in technical terms, when it is at its liquidlimit. The liquid limit of a soil is the moisturecontent at which it becomes a fluid. Fig. 5.1(a)shows soil that is still too dry and Fig. 5.1(b) soil atthe correct moisture content. If the soil is too wet itwill slump when the mould is removed.Clayey soils require the addition of straw beforethey are moulded to distribute the cracking that willdevelop as the soil dries just as mesh reinforcementdistributes the shrinkage cracking of a concrete slab.The straw should not be more than 50mm in length,and about as much as can be picked up on one handis required per block. The soil should be slightlyoverwet before the addition of the straw because thestraw will absorb some moisture. At that moisturecontent the straw can be easily and thoroughlymixed into the soil. Fig. 5.2(a) shows, on the left, ablock containing straw that is too long and intowhich the straw has not been effectively mixed,probably because the soil was too dry when it wasmoulded and, on the right, a block into which thestraw has been thoroughly mixed. The two blocks inFig. 5.2(b) show how the straw distributes thecracks in adobe blocks. The block on the rightcontains no straw and has cracked in two while thestraw in the block on the left had dispersed thecracking.A soil that is deficient in clay content and isstabilised with cement is not prone to cracking as itdries so straw is not required. The soil should beeven more overwet before the addition of thecement. The degree of overwetting is bestdetermined by trial moulding of single blocks.

Fig. 5.1 The soil in (a) is too dry for adobe construction and the soil in (b) is at the correct moisturecontent

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Fig. 5.2 The use of straw in adobe blocks. Photograph (a) shows the appearance of adobe blocksone with too much straw and the other with the correct quantity of straw. Photograph(b) shows the crack-distributing effect of straw. Both the blocks were made from the sameheavy clay, but the one without straw has cracked into two pieces.

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5.2 Moulding blocksThere is no standard size for adobe blocks, thechoice depending upon the thickness of the walls,bond requirements, and weight limitations. Theminimum thickness of exterior wall is 250 mm. Toachieve bond the length of block is usually 1.5 timesthe width. The most frequently used height of blockis 100 mm, but 125 mm is also commonly used.With clayey soils small blocks dry more evenly andcrack less as a general rule.The approximate weights of some common blocksizes is as follows:

Dimension Weightmm kg

Width Length Height125 250 90 5.5250 350 100 16250 375 100 17250 375 125 21300 300 125 19300 450 100 23

The sequence of operations in moulding adobeblocks is as follows: Sufficient soil to make about 10 blocks is

brought to the correct moisture content, thestraw or cement is added and the moisturecontent is again checked. The addition ofstraw or cement reduces the effectivemoisture content and the addition of morewater is usually required.Alternatively, if the soil has been made toowet initially some drying is effected by theseadditions.

The soil mixture is placed in the mould andpressed into the corners to ensure sharpcorners and edges. Note that the mould hasparallel sides and is lined with sheet metal.Before being filled with soil the mould islightly oiled. Depending upon the particularsoil the mould will need to be cleaned andre-oiled at intervals or following aninterruption to block-making.

The mould is immediately lifted off theblock. Soil at the correct moisture content formoulding will not cling to the mould and asmooth finish on the blocks will be achieved.There should be no evidence of strawprojecting from the block.

Fig. 5.3 shows these operations and the standard ofblock that should result.Fig. 5.4 (a), (b) and (c) shows the use of a multiplemould for adobe blocks. Such a mould can be usedonly if two people are available to lift it as thelifting action must be smooth and straight up. Anyrocking or horizontal movement of the mould willdamage or distort the blocks.

Fig. 5.5 shows a machine used for the commercialproduction of adobe blocks in New Mexico andFig. 5.6 shows a typical commercial adobe yard inwhich such machines are used. Even though themixing, transporting and moulding operations havebeen mechanised they still simulate the manualmanufacturing processes.

Blocks of different shapes or sizes needed forspecial purposes may be cut or sawn from thestandard blocks but if they are required in largenumbers special moulds would be justified.A textured face can be obtained by substituting thedesired pattern for one plain face of the mould. Suchpatterns must necessarily be fairly coarse to becompletely filled by the soil. Also the moisturecontent of the soil must be very closely controlled toensure that the soil does not adhere to the mould andyet does not slump. Soil containing stone wouldneed to be sieved if it is proposed to use it in thisway. Examples of the effects that can be achievedand of the moulds used are shown in Fig. 5.7(a) and(b).

The area on which adobe blocks are to be castshould be level, well drained and cleared of longgrass. The ground should be firm and free fromloose material. If the blocks are to be cast on aconcrete slab the surface should be covered with alayer of sand to allow the block to dry uniformly.Blocks cast on plastic sheet develop quite significantwarping because of the differential rates of drying oftop and bottom.

After about a week, at most, the blocks are tippedon to one side and allowed to dry for a further weekor so when they can be stacked to dry completelybefore being used. At this stage the blocks should beprotected from rain in such a way that the freecirculation of air is possible. Fig. 3.5 shows blocksstacked in a suitable manner. Blocks should not beused before they have dried for at least four weeksin favourable weather.

Blocks made of soil having a high clay contentshould be dried slowly. This is achieved by coveringthem with shade cloth or bagging in very hotweather. If extreme measures are necessary toprevent cracking of the blocks it might be advisableto look for an alternative source of soil.

Cement-stabilised blocks should not be allowed todry out like straight soil blocks. They should becovered with moisture-proof building paper orplastic sheet for at least 24 hours. Cement-stabilisedblocks can be used when they are 7 days old.

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(a) (b)

(c) (d)

(e) (f)

Fig. 5.3 - The sequence of operations in moulding an adobe block

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Fig. 5.4 The use of a multiple mould for making adobe blocks

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Fig. 5.5 - Mechanical moulding of adobe blocks in New Mexico

Fig. 5.6 - Commercial adobe block yard in New MexicoFigs. 5.5 and 5.6 reproduces from Adobe bricksin New Mexico by courtesy of Edward W. Smith

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Fig. 5.7 - Decorative adobe blocksIn (a) the block has been cast to an ornamentalshape and in (b) the block has been cast withpatterned exterior face

5.3 Laying blocksAdobe blocks are laid in the walls in a mannersimilar to that for stone or concrete blocks. Theyshould be properly bonded, particularly at cornersand the junctions of partition walls. Typical bondingis illustrated in Fig. 5.8.Mud mortar, consisting of the same material as theblocks, is the most suitable and is the mosteconomical. The earth for the mortar should be wellscreened to leave no stones over 6 mm in the mix.Straw should not be included in the mortar.Fig. 5.9 and 5.10 show examples of the quantity ofconstruction that can be achieved by owner buildersusing adobe blocks.

Fig. 5.8 - Typical bonding of adobe blocks

Fig. 5.9 - Owner-built adobe house

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Fig.5.10-Owner-built adobe house Courtesy Ian Factor

5.4 Holding-down boltsHolding-down bolts are installed in mud-brick wallsby one of the following methods: drilling holes in blocks and threading them

over the bolts. pre-casting holes in the blocks and installing

as is done with drilled blocks as shown inFig. 1.5.

casting blocks split longitudinallyand placingone half of the block on either side of thebolt as shown in Fig. 5.11.

Fig. 5.11- Installation of holding-down bolts with split blocks

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SECTION 6PRESSED SOIL BLOCK CONSTRUCTION

6.1 Cinva-ram construction6.1.1 Preparation of soil6.1.2 Moulding of blocks6.1.3 Mortar6.1.4 Wall construction6.1.5 Holding-down bolts6.2 Mechanically pressed-soil block construction6.2.1 Block-making machines6.2.2 Preparation of the soil6.2.3 Moulding of blocks6.2.4 Mortar6.2.5 Wall construction6.2.6 Holding-down bolts

6.1 Cinva-ram construction6.1.1 Preparation of soilFor Cinva-ram block manufacture the soil must befree of particles larger than 6mm and this means thatmost soils have to be screened.After screening the soil is mixed with the requiredamount of cement and brought to the correctmoisture content. Cement should be added to thesoil in batches that can be moulded into blocks inabout an hour as the effectiveness of the cement willbegin to decrease after the time. Soil that has notbeen moulded into blocks 1 hour after the additionof cement should be discarded.The moisture content of the soil-cement mixture isvery important. A simple test is described inChapter 4 and shown in Fig 4.1.6.1.2 Moulding blocksThe Cinva ram is shown in Fig. 6.1. It consists of aheavy steel box with a steel lid. The bottom of thebox is raised by the action of a lever arm. Whenmoved in one direction the lever arm reacts againstthe lid and the block is compressed, and whenmoved in the other, with the lid open, thecompressed block is extruded from the mould.The steps in moulding a block are illustrated in Fig.6.2(a) to (h) and are as follows:

With the lever in the rest position and the lidopen the box is filled with prepared soil-cementmix. A few trials with a particular soil arenecessary to determine whether the soil should beloosely placed in the box or more closely packedby being tamped.

Closing the lid skims off any excess soil. Thelever is brought to the vertical and the rollers seatin the recesses on the top of the lid. Thelever-retaining latch is lifted and the compressionstroke commenced.

The compression stroke is completed with thelever in the horizontal position. If there isinsufficient soil in the box this will require verylittle effort. If the box is too full the lever willnot be able to be depressed to the horizontal. Thecorrect amount of compaction is achieved whenthe lever can be fully depressed without excessiveeffort by one person. The lever should never bepulled down by two or more people.

The lever is returned to the rest position and thelid is opened.

The block is ejected from the mould by pullingthe lever down in the opposite direction.

The block is removed from the mould base andstacked for curing.

The lever is returned to the rest position and thecycle is begun again.

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Fig. 6.1 - The Cinva-ram

(a) (b)

Fig. 6.2 - Steps in moulding a Cinva-ram block

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(c) (d)

(e) (f)

(g) (h)

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Cinva-ram blocks must be protected from rain,drying winds and extreme cold during the initialsetting period of at least 24 hours. Once set theyshould be stacked and wrapped in plastic for afurther 5 days.While it is possible for one person to produceCinva-ram blocks, the rate of production will bemore than doubled if two are employed. Fig. 6.3shows an idealised production layout for Cinva-ramblocks.Two people mixing their own soil, can produceabout 300 blocks in a day. This average figure can

be exceeded as the operators become moreexperienced. With additional people to prepare soil,stack blocks and so on this output can be at leastdoubled.Cinva-ram blocks can be made solid or with frogsand in other shapes by placing different inserts inthe mould. Fig. 6.4 shows an attachment to producehalf blocks. It consists of a cutting blade the heightof the compressed block. During the compressionstroke the blade is forced up through the soil and theblock can be removed in two halves as shown inFig. 6.5.

Fig. 6.3 - ldealised production layout for Cinva-ram production

Fig. 6.4- Cutting attachment for the Cinva-ram Fig. 6.5 - Half size Cinva-ram blocks cast withfor casting half blocks cutting attachment

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6.1.3 MortarThe mortar is usually the same soil as used for theblocks blended with cement and with hydrated limeto give workability. A suitable mix consists of onepart of cement, two of lime and nine of soil.6.1.4 Wall constructionExternal Cinva-ram walls must be two bricks thick,that is, 300 mm. The two leaves should be laid instretcher bond with ties or header blocks to connectthe leaves together. Internal walls are of single leaf150 mm in thickness. The top plate is fixed to aCinva-ram wall with threaded rods brought upthrough the centre of the wall. Flat-iron straps asused in cavity brick construction can be used withCinva-ram block external walls as the straps can beconcealed in the vertical joint between the twoleaves. Fig. 6.6 shows the bonding of Cinva-ramblock walls. Fig. 6.7 shows a house built of Cinva-ram type blocks and Fig. 6.8 shows demonstrationwalls of Cinva-ram blocks in the NBTC grounds.6.1.5 Holding-down boltsThe installation of holding-down bolts in Cinva-ramtype walls presents no problem as they can bebrought up between the two leaves.Alternatively the machine can be modified to castholes in the blocks as shown in Fig. 6.9.

6.2 Mechanically pressed-soil block construction6.2.1 Block-making machinesThe pressed-block making machines fall into twobroad categories, those which mechanically feed thesoil into the mould and those which have to bemanually fed.The mechanically fed machines are capable of muchhigher production rates but are more selective in thetypes of soil they can process.As a general rule mechanically fed machines arelimited to soils that are free flowing at the optimummoisture content for compaction. With manually fedmachines there is no restriction on the soil placed inthe mould. However not many soils appear toproduce satisfactory blocks and the full evaluationprocedure described in Section 2 needs to befollowed before a commitment to full scaleproduction is made.Fig. 6.10 shows some of the machines available inAustralia for the commercial production of pressed-soil blocks.

6.2.2 Preparation of the soilThe method of preparation of the soil will bedependent upon the soil itself and the machine inwhich it is to be used.

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Fig. 6.7 - A house built of Cinva-ram type blocks

Fig. 6.8- Demonstration walls built of Fig. 6.9 - A Cinva-ram block cast with holes forCinva-ram on the NBTC grounds cyclone bolts or vertical reinforcement

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(a) mechanically fed machine

Fig. 6.10 - Pressed-soil block making machines

(b) manually fed machine (mould inset)

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Factors that must be considered are whether or not the soil needs to be screened whether or not the soil requires cement

stabilisation the moisture content of the soil rate of production of the machine the method of mixing the soil the method of feeding the soil into the mould or

into the machines receiving hopper.If cement is to be mixed into the soil it should onlybe mixed in batches that can be moulded into blockswithin 1 hour of the cement being added to the soil.Soil that has not been moulded into blocks within1 hour of the cement being added should bediscarded.Because of the relatively small amount of soil usedin each block and the rate of production it isessential that each batch of soil be very uniformbefore being fed into the machine.6.2.3 Moulding of blocksThe procedure for moulding blocks peculiar to themachine being used must be followed.After moulding blocks should be stacked andprotected from damage by the weather.

Cement-stabilised blocks should be kept wrapped inplastic to cure for at least 7 days and longer ifpracticable.6.2.4 MortarThe mortar is usually the same soil or soil/cementmixture as used for the blocks with any particleslarger than 3mm sieved out.Because of their regular shape and hence thinnermortar joints it is common practice to useconventional mortars with pressed blocks. Forexposed walls steps must be taken to ensure thatsuch mortars are waterproof.6.2.5 Wall constructionPressed blocks are usually the full thickness of thewall and of a length that give adequate bonding atcorners.

Fig. 6.11 shows pressed block construction inprogress and Figs. 6.12 and 6.13 show the quality offinish that can be achieved.6.2.6 Holding-down boltsMechanically pressed soil blocks are usually boredto take holding-down bolts.If the inner face of the wall is to be renderedgalvanised straps can be used and concealed by therender.

Fig. 6.11 - House incorporating pressed-soil blocks under construction

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Fig. 6.12-Timber framed house with cement-stabilised pressed-soil blocks as in-fill walls Courtesy Sun Earth Homes

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Fig. 6.13-House with load-bearing cement-stabilised pressed-soil block walls Courtesy Sun Earth Homes

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APPENDIX A -METHOD OF DETERMINING THENECESSARY DEPTH OF EMBEDMENTAT HOLDING-DOWN BOLTS.Fig. A.1 - Section of wall harnessed byholding-down bolt.

Fig A.1 shows the section of wall harnessed by eachholding-down bolt. The weight of soil so harnessed is givenby:

W = dst (D - s/4) (A-1)where W is the weight of wall harnessed (kg)d is the density of the wall (kg/m3)s is the spacing of the holding-down bolts (m)D is the depth of embedment of the bolts (m) andt is the thickness of the wall (m)

The weights of some commonly used roofing systems aregiven in Table A.1 and the uplift pressure induced by arange of wind spaces on a 10-degree pitched roof is givenin Table A.2.

Table A.1 - Weight per square metre of some commonroofing systemsMaterial* Weight Per Square MetreAluminium, corrugated sheeting 9.25Slate 41.0Steel, corrugated 12.25Tiles, terra-cotta 65.5Concrete 60.5* Roof framing 100 50 softwood rafters at

450 c/cs and 38 25 softwood battens at 300 c/cs

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Table A.2 - Uplift pressure on a 10-degree pitchedroof subject to a 20-60 m/s wind.Wind speed (m/s) Uplift pressure ** (kPa)20 0.1230 0.5440 0.9650 1.5060 2.16** Higher pressures will occur at eaves and corners.Table A.3 - gives an indication of the uplift forcethat must be resisted by the holding-down bolts of a10-degree roof.

Table A.3 - Uplift force per m of a 10 degreepitched roof for different spans.

Uplift force (kN)Span Wind Speed (m/s)(m) 40 50 605 4.8 7.5 10.810 9.6 15.0 21.615 14.4 22.5 32.420 19.2 30.0 43.2

From the values in tables A.1, A.2 and A.3 and EqnA-1 it is possible to check the depth of embedment oftie-down bolts required for the proposed construction.

APPENDIX B -THE APPLICATION OF CEMENT-RENDER TOEARTH-WALL CONSTRUCTIONB.1 GENERALThe procedure described in this Appendix wasdeveloped for rammed-earth but has been used withequal success on adobe and pressed-soil blockconstruction.B.2 METHODS OF KEYING RENDER TOWALLRender can be keyed to earth walls by the followingmethods:(a) roughen the wall surface and moisten it slightly,

then apply a cement-rendering scratch coat ofplaster. Next, while this is still green, nail it tothe wall with flat-headed nails a little longer andthinner than normally used for nailing wood and,finally, apply the finishing coat.

(b) bore cone-shaped indentations about 25 to35 mm deep at 150 mm centres with areamer-type bit. In the centres of theindentations drive spring-head roofing nailsuntil the heads are flush with the wall surfaceas shown in Fig. B.1. Care is necessary duringrendering to ensure that the render is forcedbehind the nail heads as shown in Fig. B.2. Themethod is equally applicable to internalrendering except that the indentations can be at300 mm centres.

(c) large-mesh wire netting stapled to the wall.B.3 RENDER MIXA render mix that has proved to be satisfactory onearth walls consists of

1 part normal portland cement4 parts clean sand

A small amount of lime or other plasticiser may beadded if the mix lacks workability.B.4 APPLICATION OF RENDERThe render is applied in two coats, each about 6 mmthick. The wall is moistened and the first coat isthrown against the wall to provide a rough surfacefor the second coat.The second coat is applied with a trowel to producea smooth finish or it may be spattered on to producea rough-cast finish.Cement render should not be applied to walls whenthe sun is shining on them, and should be kept moistfor 1 to 2 days after completion.B.5 INTEGRAL CONSTRUCTION OF RENDERCOAT AND RAMMED-EARTH WALLA method of forming the render coat integrally witha rammed-earth wall was used by the author toconstruct the demonstration walls in the NBTC