Ž .Construction and Building Materials 15 2001 323�330

Review Article

Masonry walls: materials and construction

Emeritus A.W. Hendry�

Uni�ersity of Edinburgh, 146 � 6 Whitchouse Loan, Edinburgh EH9 2AN, UK

Received 25 May 2001; accepted 30 June 2001

Abstract

This paper offers a review of contemporary masonry wall construction beginning with a brief statement of the applications and advantages of this form of construction. Masonry materials include clay, concrete and calcium silicate in which a wide variety of unit sizes, forms and colours are produced. Mortars are usually cement�sand with either lime or a plasticiser added to improve workability. In recent years new types of mortars have been developed including thin bed mortars for use with accurately dimensioned units and mortars with improved thermal properties. Design considerations for load bearing and non-load-bearing walls are summarised and construction methods and site practices, aimed at improved economy and productivity, are described. A list of key references is included. � 2001 Elsevier Science Ltd. All rights reserved.

Keywords: Masonry; Walls; Units; Mortar; Construction

1. Applications and advantages of masonry construction

Although in the 20th century masonry was displaced for many applications by steel and concrete, it remains of great importance for load bearing walls in low and medium rise buildings and for internal walls and cladding of buildings where the structural function is met by one or other of these newer materials. The market for masonry construction may be divided into

� �housing and non-housing sectors 1 , the latter includ- ing industrial, commercial and educational buildings in addition to a wide variety of buildings used for adminis- trative and recreational purposes. There is also a limited use of masonry construction for infrastructure, e.g. for

� �retaining walls 2 . In all sectors there is a significant requirement for masonry in the repair and mainte-

� �nance of existing buildings 3 . For certain applications the low tensile strength of

masonry is a limiting factor in situations where con- siderable lateral forces have to be resisted. Reinforced

� Tel.: �44-131-447-0368.

masonry can be used to overcome this limitation in buildings in seismic areas and generally where non- load-bearing panels are subjected to substantial wind loads. Walls of cellular or T cross-section are particu- larly suitable for large, single cell buildings where the adoption of such walls is greatly extended by post-ten-

� �sioning 4 . Masonry wall construction has a number of advan-

� �tages 5 the first of which is the fact that a single element can fulfil several functions including structure, fire protection, thermal and sound insulation, weather protection and sub-division of space. Masonry materi- als are available with properties capable of meeting these functions, requiring only to be supplemented in some cases by other materials for thermal insulation, damp-proof courses and the like.

The second major advantage relates to the durability of the materials which, with appropriate selection, may be expected to remain serviceable for many decades, if not centuries, with relatively little maintenance. From the architectural point of view, masonry offers advan- tages in terms of great flexibility of plan form, spatial composition and appearance of external walls for which

0950-0618�01�$ – see front matter � 2001 Elsevier Science Ltd. All rights reserved. Ž .PII: S 0 9 5 0 – 0 6 1 8 0 1 0 0 0 1 9 – 8

( )E.A. Hendry � Construction and Building Materials 15 2001 323�330324

materials are available in a wide variety of colours and textures. Complex wall arrangements, including curved walls, are readily built without the need for expensive and wasteful formwork.

The nature of masonry is such that its construction can be achieved without very heavy and expensive plant. Although dependent on skilled labour for a high standard of construction, productivity has been main- tained by the use of larger units, improved materials handling and off-site preparation of mortar.

The advantages of masonry wall construction are therefore considerable but, as with all materials, ap- propriateness to the application has to be considered, assuming acceptability from the architectural view- point. For example, if the masonry is not to be load bearing it will be necessary to consider the implications of the weight of the masonry as it affects the support- ing structure. If the walls are to be load bearing, it will be important to ensure that their layout is consistent with overall stability and with avoidance of failure in the event of accidental damage. This implies that the function of the building is such that there will be a sufficient number of walls to meet this requirement, as for example, is likely to be the case in a hotel or other similar building. On the other hand, a requirement for wide, open plan space is unlikely to be appropriate for a load bearing wall structure although masonry may be suitable in such a case as a cladding to a steel frame building. From the construction point of view, availabil- ity of the necessary skilled labour, the construction time and its phasing with the overall building schedule will also be relevant factors at the preliminary design stage in deciding to use masonry walls.

2. Masonry units and mortar

Masonry walling units in the form of bricks and blocks are produced from clay, concrete and calcium silicate. Natural stone is also used but in current prac- tice only to a limited extent and will not be discussed in this brief review. All units have broadly similar uses although their properties differ in important respects depending on the raw materials used and the method of manufacture. Bricks and blocks are produced in many formats, solid, perforated and hollow. Bricks are

Ž .typically 215 � 102 � 65 mm length � width � height whilst conventionally sized blocks are available in lengths 400�600 mm, heights 150�300 mm and a wide range of thicknesses between 60 and 250 mm.

The following physical and mechanical properties of masonry units are relevant to their use in the construc- tion of walls:

� Colour; � Surface texture;

� Weight; � Absorption and pore structure; � Thermal conductivity; � Thermal and moisture movement; � Fire resistance; � Compressive strength; and � Tensile strength.

� �Clay bricks 6,7 are produced in a variety of colours depending on the mineral content and firing tempera- ture, most commonly in shades of red but facing bricks in yellow, buff and brown and with roughened surface

� �texture are frequently selected. Calcium silicate 8 and concrete bricks are usually light grey and other paler shades and tend to give a more uniform appearance to a wall than clay bricks. Concrete blocks are normally grey but if an enhanced appearance to exposed faces is required this can be achieved by painting, plastering or by the use of special blocks having a surface textured in one of a number of possible ways in the course of manufacture e.g. by tooling the surface or by exposing the aggregate.

The density of clay, calcium silicate and concrete is approximately 2 t�m3 but the weight of units which is of more importance in construction depends on their size, shape and type i.e. whether solid, cellular or perforated. Various lightweight materials are available,

Ž . � �in particular, aerated autoclaved concrete AAC 9 , with a material density in the range 450�850 kg�m3 which enables quite large solid units to be handled without mechanical assistance.

The absorption and pore structure of bricks and blocks varies widely and is important in a number of ways. Thus certain clay bricks which absorb between 4.5 and 7.0% of their weight can be used as a damp- proof course material. Highly absorptive clay bricks, on the other hand, may remove water from the mortar preventing complete hydration of the cement. Absorp- tion is of less relevance in the case of calcium silicate and concrete units but pore structure affects resistance to frost damage.

Thermal conductivity of units is of great importance in satisfying design requirements. There is not a great deal of difference between solid units in clay, calcium silicate and dense concrete but lightweight aggregate and AAC blocks have substantially lower thermal con- ductivity than the heavier materials, typically 0.11 W

Ž .per meter thickness per degree Celsius W�mK as compared to 0.84 W�mK for clay bricks. Hollow and perforated clay and concrete units will have intermedi- ate values depending on their characteristics. In prac- tice, however, the insulating properties of complete walls depend on a number of factors in addition to the thermal properties of the units.

Thermal and moisture movements in masonry walls require to be taken into account in design of walls and

( )E.A. Hendry � Construction and Building Materials 15 2001 323�330 325

� �depend on the characteristics of the units 10 , thus clay units tend to expand in service whilst concrete and calcium silicate units shrink.

Masonry materials are inherently resistant to fire and the critical factor, in this respect, lies in the detail

� �design of the construction 11 aimed at preventing fire passing through defects in or finding a way around a wall.

Having regard to the mechanical properties of ma- sonry units, the most important is compressive strength which, as well as being of direct relevance to the strength of a wall, serves as a general index to the characteristics of the unit. It is measured by a standard- ised test, the result depending to some extent on the conditions prescribed in the particular standard being used. It is important to note also that the apparent compressive strength obtained depends on the dimen- sions and type of the unit. Thus, if a brick and a block of larger overall dimensions but of the same material were tested, a higher figure would be obtained for the

� �brick as a result of the ‘platen effect’ 12 . This results from the restraint to lateral deformation by the testing machine platens having more effect in a squat speci- men like a brick than in a block which is taller in proportion to its thickness. A recent code of practice,

� �Eurocode 6 13 attempts to standardise unit strength by adjusting the standard test value by a factor depend- ing on the unit proportions.

Clay bricks are obtainable in strengths of up to 100 N�mm2 but much lower strengths, say 20�40 N�mm2 are generally sufficient for domestic buildings and for cladding walls for taller buildings. Concrete blocks have lower apparent compressive strengths � in the range 2.8�35 N�mm2 � but the effect referred to above has to be kept in mind in making comparisons. Further- more, blockwork constructed from units of the same nominal compressive strength will generally have a higher strength than the corresponding brickwork.

The tensile strength of masonry units � both direct and flexural � has an influence on the resistance of masonry under various stress conditions but is not normally specified except in relation to concrete blocks used in partition walls where typically a breaking strength of 0.05 N�mm2 is required.

Although mortar accounts for as little as 7% of the total volume of masonry, it influences performance far more than this proportion indicates. Mortar requires to have certain properties prior to setting, particularly workability. Hardened mortar has to be sufficiently strong and to develop adequate adhesion to the units and also to set without excessive shrinkage which would reduce the resistance of the masonry to rain penetra- tion or even cause cracking of the units. It should also be capable of accommodating some degree of move- ment in the masonry resulting from creep or thermal effects without cracking. Conventional mortar mixes

� �14 are based on Portland cement, lime or plasticiser and sand, and are graded according to compressive strength. The stronger the mortar the less able it is to accommodate movement so that it is inadvisable to use a stronger mix than is necessary to meet structural requirements. A compressive strength of 2�5 N�mm2 is adequate for most low-rise structures. For special purposes a type of cement other than ordinary Port- land cement may be used, e.g. a sulfate resisting variety for brickwork below damp-proof course level where ground water is contaminated by sulfates.

A workable mortar has a smooth, plastic consistency which is easily spread with a trowel and readily adheres to a vertical surface. Well graded, smooth aggregates enhance workability as do lime, air entrainment agents Ž .plasticisers and proper amounts of mixing water. Lime imparts plasticity and ability to retain water in the mix whilst plasticisers improve frost resistance. Thin bed

� �mortars 15 with a 1:2 cement�sand mix together with water retaining and workability admixtures are increas- ingly used with accurately dimensioned units.

In addition to units and mortar, masonry wall con- struction requires the use of a number of subsidiary components including damp-proof course material, cav- ity trays, wall ties and fixings. Each of these must be as durable as the masonry itself as well as meeting its particular function. Suitable damp-proof course materi-

� �als 16 for general use include bitumen composites, pitch polymer and polythene. Sheet copper or high strength engineering bricks may be used in highly stressed load-bearing walls. Pre-formed cavity trays and roof flashings are available and are to be preferred for ease and accuracy of installation.

In cavity wall construction, the leaves have to be tied � �together with suitable wall ties 17 . Several types are

used and are made in galvanised or stainless steel. The latter are more expensive but are far more durable so that the extra cost, which is marginal in the cost of a wall, is fully justified in external walls in exposed situa- tions. Special ties are available for repairing walls in which the ties have been incorrectly placed or omitted

� �or have become ineffective as a result of corrosion 18 . Fixings are also required between masonry walls and

� �concrete or steel frames 19 which, as well as being resistant to corrosion, must be capable of permitting differential movement between the wall and the main structure. Other components include light ties for con- necting brickwork cladding to timber frames and for

� �supporting timber joist floors from masonry walls 20 .

3. Structural design

Structural design of masonry walls is carried out according to national codes of practice, in the UK BS

� � Ž5628 21 or Eurocode 6 currently issued in the form of

( )E.A. Hendry � Construction and Building Materials 15 2001 323�330326

� �.ENV 1996-1-1 13 . Both these codes are based on limit state principles, safety being assured by the use of characteristic values of loads or actions and material strengths together with partial safety factors, applied as a multiplier to loads and as a divisor to strengths. Characteristic values are intended to represent a 95% confidence limit of not being exceeded in the case of loads and of being attained in the case of strengths. Partial safety factors are to allow for uncertainties in estimating loads and material strengths including short- fall of site from laboratory values. The system is in- tended to achieve a low probability of failure, of the order of 10�6 , and permits some differentiation between load cases, materials and levels of workman- ship. Other countries, including the US, continue to use permissible stresses as the basis of design without

� �stated safety factors 22 . This leads to simpler calcula- tions but without the facility to adjust the design to accommodate perceived differences e.g. in load condi- tions, material properties and workmanship levels.

Primary variables in the calculation of the compres- sive strength of a masonry wall, in addition to the unit strength, include the eccentricity of loading and the slenderness ratio of the wall. Both of these are difficult to assess on a theoretical basis depending as they do on

� �interaction between walls and floors 23 and on the presence of interconnected walls. Allowance for eccen- tricity and slenderness in design requires, in turn, the availability of a capacity reduction factor and a variety of theories on which to base this have been developed.

Further complications arise from imperfections in construction such as lack of verticality, bowing and lack of alignment of walls from one storey to the next. Creep effects may be significant in some walls, in some cases, this may increase the eccentricity at mid-height of a wall but where there are interacting floor slabs the eccentricity may reduce with time. Compressive

� �strength of walls is thus a complex problem 24 and a considerable amount of research work has been carried out on it over many years.

The shear strength of masonry walls has to be con- sidered in the design of multi-storey buildings to resist wind loads and in all situations where seismic effects are encountered. Investigations have been undertaken

� �on large-scale structures 25 and on small specimens to � �develop test methods for material strength 26 .

A further aspect of design which has received partic- ular attention in the UK and Australia concerns the lateral resistance of wall panels to wind loading and also in relation to accidental damage. Although a con- siderable amount of research has been reported on the

Ž � �resistance of masonry walls to wind loads cf. 23 pp. .153�180 it has proved difficult to resolve and the

design method given in the British and European codes is of a semi-empirical nature. Attention was first di- rected to the problem of accidental damage as a result

of a gas explosion although this was not in a masonry structure. In this context it was realised that if a masonry wall carried a high enough compressive load its lateral strength would be sufficient to resist the pressure resulting from a domestic gas explosion and could therefore be assumed to remain in place fol- lowing such an event. Regulations were introduced to ensure that in buildings of five or more storeys, damage resulting from a gas explosion or any other accident would not be disproportionate to the cause. A substan-

� �tial effort 27,28 was undertaken when these require- ments were brought in to demonstrate that with ade- quate design brick masonry buildings would comply. It is, however, not possible to avoid extremely severe damage to low rise buildings of whatever construction from gas explosions although the risk of loss of life is smaller than in multi-storey buildings.

4. Non-structural design factors

The following factors have to be taken into account in the design of masonry walls:

� Movement; � Moisture exclusion; � Durability; � Thermal and acoustic properties; and � Fire resistance.

� �Movement takes place in all masonry materials 29 as a result of applied stress, moisture and temperature change, chemical reactions. These effects, as well as foundation movements, can lead to cracking of the wall � �30 . Movements due to loading may result from stress- ing of the masonry, which may be significant in multi- storey buildings, and may develop either immediately

Ž .after the application of the loads elastic deformation Ž .or over a period of time creep . Movement in adjoin-

ing elements may affect masonry walls, for example, the deflection of supporting beams may induce tensile stresses in the supported wall or horizontal movements in a beam or lintel supported by a wall may induce cracking in the latter. Again, non-structural walls be- neath beams or slabs, but not intended to support them may become loaded as a result of the deflection of these elements resulting in damage to the wall.

Thermal movements depend on the coefficient of expansion of the material and the range of temperature experienced. Coefficients of expansion for various ma- terials are given in codes of practice but the tempera- ture range to be assumed in design is more difficult to establish since it depends on such things as colour, exposure and orientation as well as climatic factors. In the UK, the temperature range experienced by a heavy exterior wall has been quoted as from �20�C to �65�C

( )E.A. Hendry � Construction and Building Materials 15 2001 323�330 327

with a datum temperature from which movements are assumed to take place of 10�C.

Dimensional changes take place after manufacture of masonry units: expansion in the case of clay bricks; and shrinkage in the case of concrete and calcium silicate products. Dimensional changes also take place in service following change of moisture content. If movements are suppressed, very large forces can be set up so that at the design stage provision has to be made for them to take place without resulting in unaccept- able cracking. This is achieved by the selection of suitable materials and by careful detailing rather than by calculation although it may be necessary to estimate

� �differential movement in multi-storey cavity walls 31 and between masonry cladding and a steel or concrete structure in a multi-storey building.

Although masonry materials are relatively stable, some chemical conditions can affect dimensional stabil- ity. Thus, under certain conditions carbonation of open textured concrete products and mortar can result in additional shrinkage to the extent of approximately 25% of the free moisture movement. Portland cement mortar is subject to attack by dissolved sulfates result- ing in disruption of the masonry.

Unsatisfactory foundation conditions are a common cause of cracking in masonry walls which have a limited tolerance for uneven settlement. Conditions requiring particular care include shrinkable clay soils, mining

� �subsidence and filled ground 32 . The prevention of moisture penetration is a critical

factor in the design of masonry walls requiring careful selection of materials in relation to exposure condi- tions, correct detailing and achievement of a good standard of workmanship. Exposure conditions are specified in national codes, for example, in the UK these are given in six categories of severity which are

� �defined in BS 5628 Part 3 33 and related to minimum thicknesses of masonry walling. Certain architectural features, such as overhangs and drips, are advanta- geous in keeping water off a wall. On the other hand, large areas of glazing or impermeable cladding can lead to excessive quantities of rain water running on to the masonry thereby increasing the possibility of rain penetration. Inclusion of damp-proof courses is neces- sary to prevent ground moisture from rising into a wall and the penetration of rainwater at openings and at roof level. Cavity wall construction requires the use of cavity trays to prevent water, which may come through the outer leaf from bridging the cavity. In some cases, where a steel or concrete frame is clad in masonry, this can give rise to complex details which are difficult to build.

Durability may be regarded as the ability of a mate- rial or construction to remain serviceable for an ac- ceptable length of time without excessive or unex-

� �pected maintenance 34 . What constitutes an accept-

able period is not easily defined but the majority of buildings are expected to have a life of many decades. Factors which affect durability include: frost action; salt crystallisation; and the effect of certain biological agencies. Of these, frost damage is likely in most situa- tions to be the most important and results from the freezing of water in the pores of the material. Thus, ice forming first at the surface of a masonry unit entraps water in the sub-surface layers and as this freezes and expands pressure is built up which may be sufficient to cause spalling of the face of the unit. The mechanism of failure is complicated and depends on a number of factors including the pore structure of the material, the degree of saturation and the rate of freezing. Repeated freeze-thaw tests have been devised to give an indica- tion of the resistance of masonry to frost damage but experience is the most reliable guide for any given location. Construction which is persistently wet and is exposed, as for example, in a parapet or free standing wall, is the most vulnerable.

Salt crystallisation is essentially a physical process, somewhat analogous to freezing, whereby salt solution is carried into the masonry from ground water or from pollutants. In warm weather the moisture evaporates and the dissolved salts crystallise in the pores below the surface of the material to form a hard skin which may then flake off to reveal a new surface to the same process.

Atmospheric pollution, resulting from the burning of fossil fuels, can result in masonry being exposed to sulfur and nitrogen acids. Sulfur dioxide is a widespread pollutant which combines with water to produce sul- furous acid which attacks tricalcium aluminate in ce- ment mortar. Certain types of natural stone which have a pore structure comprising many pores of small di- ameter are particularly susceptible to damage by pollu- tion.

Many varieties of algae, lichens, mosses and even � �bacteria 35 as well as higher plants can establish

themselves on the surface of a masonry wall and, having penetrated the pores of the masonry can cause damage by generating organic acids with similar effects to atmospheric pollution.

Where metal components are used in masonry con- struction careful selection in relation to exposure con- ditions is necessary to avoid damage to the wall. A frequent cause of premature failure of cavity walls is the use of thin galvanised wall ties in situations of

� �severe exposure 36 . In such cases ties should be of austenitic stainless steel. Similar considerations apply where light gauge reinforcement is used for example, to control cracking or to provide enhanced lateral resis- tance to wind loads.

Thermal insulation of buildings is an increasingly � �important factor in building design 37 . Masonry walls

built in conventional units of clay; concrete or calcium

( )E.A. Hendry � Construction and Building Materials 15 2001 323�330328

silicate will usually require additional insulation al- though lightweight materials such as AAC may be adequate if sufficiently thick. If thin wall masonry is used, the position of the insulation is important in relation to the thermal behaviour of the wall. Thus, if the insulation is internal the wall will be relatively cold and will retain on average a higher moisture content with reduced thermal resistance. External insulation on the other hand, will result in the masonry being at a higher average temperature and drier with correspond-

� �ingly better insulating properties. Cavity insulation 38 offers a compromise in terms of thermal behaviour and can be augmented by internal insulation in the form of plasterboard. The most commonly used insulation ma- terials include: extruded polystyrene; rigid poly- urethane; and mineral fibre in sheet or roll form. Cavity insulation can also be introduced in the form of beads, fibre or foam.

Calculations relating to insulation are usually based on the assumption of steady state conditions but ther- mal mass has a significant effect on the response of a masonry building to climatic conditions. Representa- tion of dynamic thermal behaviour is possible and

� �could lead to economies in certain conditions 39 but is not often attempted in practice.

Condensation in buildings, which may result in da- � �mage to decorations and mould growth 40 , can be

caused by inadequate insulation and ventilation. As a precaution against this it is normal practice to incor- porate a vapour control layer in the form of a plastic sheet on the warm side of the insulation and to avoid thermal bridges through the insulation.

Masonry construction is generally effective in rela- � �tion to sound insulation 41,42 between occupancies

and in reducing noise nuisance from traffic. This de- pends essentially on mass but sound transmission is complicated and careful attention to detail is required to avoid the effectiveness of a wall being reduced by flanking transmission. In certain spaces, such as assem- bly halls, the reflective surface properties of masonry walls may require treatment with absorbing material to provide an acceptable acoustic ambience.

Masonry materials are incombustible and therefore inherently effective in providing fire protection for the

� �periods of time specified in building regulations 43 . Again care in detail design is essential, for example, in providing fire stops in cavities, where services pass through a wall and with perimeter details which must be such that fire will not simply by-pass the wall.

5. Masonry wall construction

Conventional methods of masonry wall construction remained virtually unchanged until quite recently, at- tracting criticism that masonry buildings take too long

to construct and that it is difficult to find the necessary skilled labour, partly because of unattractive working

� �conditions on site 44 . Efforts to improve the position have centred essentially on the use of new types of unit, innovations in site practice and pre-fabrication � �45 .

As already noted, many new types of units have been developed in recent years with improved thermal properties, greater uniformity in dimensions and in a greater variety of sizes and types. Larger, dimensionally accurate units together with the use of thin bed mor- tars, which are spread more rapidly than by traditional methods, permit significant improvements in productiv- ity. The use of large units of dense concrete or calcium silicate implies mechanical handling and the use of small cranes for this purpose is common in a number of European countries. It is now almost universal practice for units to be delivered in polythene wrapped packs of 500 bricks or equivalent number of blocks which can be moved from the delivery vehicle by crane or fork lift truck close to where they are to be laid, thus saving labour and avoiding damage or saturation by rain.

A further development in the supply of materials offered by block manufacturers in Europe is to deliver units as a package along with subsidiary materials � �46,47 for the construction of particular walls in a building thus reducing site handling and storage. On all but very small sites, mortar is delivered in pre-mixed form, ensuring accuracy of gauging and avoidance of waste.

In addition to these well established improvements � �in construction methods, a research project 48 is in

hand in the UK aimed at ‘re-engineering’ or standard- ising conventional bricklaying which will remain impor- tant for building facing brickwork into the indefinite future. The general aim is to improve productivity which may also result from the introduction in the US

� �of self-raising work platforms 49 which offer an alter- native to conventional scaffolding. It is claimed that these devices save considerable construction time and costs.

Attempts in various countries to effect improvement by the use of pre-fabricated wall panels go back at least

� �to the 1960s 50 . These met with limited success but pre-fabrication using mechanised brick laying is still undertaken in Germany. The advantages include pro- duction under factory conditions with consequent achievement of a high standard of work with available labour and acceleration of site construction. The disad- vantages lie in the high cost of plant and factory space leading to the requirement for long, continuous pro- duction runs for economic viability. There are also limitations in building design imposed by the size and shape of the panels and the problem of making connec- tions between them. The practical possibility of using pre-fabricated brickwork columns rather than walls has

( )E.A. Hendry � Construction and Building Materials 15 2001 323�330 329

� �been demonstrated 51 , overcoming the need for ex- pensive, specialised plant and some of the other prob- lems associated with this method of construction. A system of on-site, automated block laying has been devised in the USA and also marketed in Ireland under

� �the name EZ-BLOK 52 . Up to 11 hollow concrete blocks are laid end-to-end on a roller staging table and lifted simultaneously by crane using a device which clamps them together. They are placed on the wall on which a mortar bed has been pre-laid using a mortar pump. A special applicator connected to the mortar pump is used to fill the head joints. The system is designed to eliminate heavy lifting and to improve productivity.

6. Concluding comment

Masonry wall construction has undergone consider- able change in the course of the last few decades with the introduction or extended use of lightweight materi- als and new types of units. The main objectives under- lying these developments has been the need for im- proved thermal insulation and increased rate of con- struction whilst retaining the advantages of this form of construction in terms of durability, appearance and flexibility of application. Provided that economy in comparison with alternative materials can be achieved there would appear to be an excellent future for the continued use of masonry construction.

7. General references

The books listed in Section 8 will be found useful for general reference in the areas indicated by the titles. Text references are identified where appropriate through the review. A considerable number of these are Building Research Establishment Digests which give information in a form suitable for use by designers as well as references to source publications. Attention is also drawn to the proceedings of various internatio- nal masonry conferences and to the journals of the

Ž .British Masonry Society, Masonry International and Ž .The Masonry Society USA which are primary sources

for research results.

8. Bibliography

Manual for the design of plain masonry in building structures. Institution of Structural Engineers, London, 1997.

Amrhein J. Reinforced masonry engineering hand- book 5th edition. The Masonry Society, Boulder Co., 1995.

Curtin W.G., Shaw G., Beck J., Bray W.A. Structural masonry designers’ handbook, 2nd edition, Blackwell Science, Oxford, 1995.

Drysdale R.G., Hamid A.A., Baker L.R. Masonry structures: behaviour and design, 2nd edition, The Ma- sonry Society, Boulder Co., 1999.

Hendry A.W. Structural masonry, 2nd edition, Macmillan, London, 1998.

Hendry A.W., Sinha B.P., Davies S.R. Design of masonry structures, 3rd edition E. and F.N. Spon, Lon- don, 1997.

Hendry A.W., Khalaf F.M. Masonry wall construc- tion, E. and F.N. Spon, London, 2000.

Matthys J.E. editor, The masonry designers’ guide, 2nd edition, The Masonry Society, Boulder Co., 1999.

Orton A. Structural design of masonry, Longman Scientific and Technical, Harlow, 1992.

Thomas K. Masonry walls. Butterworth-Heinemann, London, 1997.

References

� �1 Masonry 2007. Department of the Environment, London 1997. � �2 Thomas K. Masonry walls. Butterworth-Heinemann, Oxford

1996. � �3 Sowden AM. The maintenance of brick and stone masonry

structures. London: E. and F.N. Spon, 1990. � �4 Hendry AW, editor. Reinforced and prestressed masonry. Har-

low: Longman Scientific and Technical, 1991. � �5 Hendry AW, Khalaf FM. Masonry wall construction. London:

Spon Press, 2000. � �6 Bricks: note on their properties. Brick Development Associa-

tion. Publ. TIP 7. � �7 De Vekey RC. Clay bricks and clay brick masonry. Digest 441.

Watford: Building Research Establishment, 1999. � �8 Calcium silicate brickwork. Digest 157. Building Research Es-

tablishment, Watford 1992. � �9 Autoclaved aerated concrete. Digest 342. Building Research

Establishment, Watford 1989. � �10 Estimation of thermal and moisture movements and stresses.

Digests 227, 228, 229. Building Research Establishment, Wat- ford 1979.

� �11 Standard method for determining fire resistance of concrete and masonry construction assemblies. ANSI�ACI216.1- 97�TMS-0216-97. The Masonry Society, Boulder Co., 1997.

� �12 Khalaf FM, Hendry AW. Masonry unit shape factors from test results. Proc Br Masonry Soc 1994;6:136�9.

� �13 Eurocode 6: design of masonry structures. Part 1-1 General rules for buildings. Rules for reinforced and unreinforced ma-

Ž .sonry. ENV 1996-1-1 CEN Brussels, 1995. � �14 Building mortar. Digest 362. Building Research Establishment,

Watford 1991. � �15 Aircrete thin joint mortar building systems. Digest 432. Build-

ing Research Establishment, Watford 1998. � �16 Damp-proof courses. Digest 380. Building Research Establish-

ment, Watford 1993. � �17 de Vekey RC. Ties for masonry walls: a decade of develop-

ment. Watford: IP 11�00 Building Research Establishment, 2000.

� �18 Installing wall ties in existing construction. Digest 329. Building Research Establishment, Watford 2000.

( )E.A. Hendry � Construction and Building Materials 15 2001 323�330330

� �19 Ties for masonry cladding. IP 17�88. Building Research Es- tablishment, Watford 1988.

� �20 Joist hangers. BRE Publ. GBG 21. Building Research Es- tablishment, Watford 1999.

� �21 Code of practice for use of masonry. Part 1 Structural use of unreinforced masonry. BS 5628 Part 1, British Standards Insti- tution, London, 1992.

� �22 MSJC Building code requirements and specification for ma- Žsonry structures ACI 530�ASCE 5�TMS 402 and ACI

.530.1�ASCE 6?TMS 602 , The Masonry Society, Boulder Co., 1999.

� �23 Hendry AW. Structural masonry. 2nd edition London: Macmil- lan Press Ltd, 1998:123�43.

� �24 Hendry AW. Comments on the design of masonry bearing walls according to ENV 1996-1. Proc Br Masonry Soc 1998;8.

� �25 Sinha BP, Maurenbrecher AHP. And Hendry A.W. Model and full-scale tests on a five storey cross-wall structure under lateral loading. Proceedings of the Second International Brick Ma- sonry Conference, Stoke on Trent 1971:201�208.

� �26 Hendry AW. Shear strength criteria and related tests for brick Ž .masonry. Adv Struct Eng 1997;1 2 :135�41.

� �27 Astbury NF, West HWH, Hodgkinson HR, Cubbage PA, Clare R. Gas explosions in load-bearing brickwork structures. Stoke on Trent: British Ceramic Research Association, 1970. Special Publication No. 68.

� �28 Sinha BP, Hendry AW. The stability of a five-storey brickwork cross-wall structure following the removal of a section of main load-bearing wall. Struct Eng 1971;49:467�74.

� �29 Grimm CT. Design for masonry volume change. The Masonry Society, Boulder Co. 1999.

� �30 Cracking in buildings. Digest 75 Building Research Establish- ment, Watford, 1966.

� �31 Hendry AW, Sinha BP, Davies SR. Design of masonry struc- tures. 3rd edition London: E. and F.N. Spon, 1997.

� �32 Site investigation for low rise buildings: the walk-over survey. Digest 348. Building Research Establishment, Watford, 1989.

� �33 British standard code of practice for use of masonry. Part 3. Materials and components, design and workmanship. BS 5628 Part 3, British Standards Institution, London, 1985.

� �34 Harding JR, Smith RA. Brickwork durability. BDA Design Note 7. Brick Development Association, Windsor, 1986.

� �35 Control of lichens, moulds and similar growths. Digest 370. Building Research Establishment, Watford, 1992.

� �36 Replacing wall ties. Digest 401. Building Research Establish- ment, Watford, 1995.

� �37 Energy efficiency in dwellings. Digest 355. Building Research Establishment, Watford, 1990.

� �38 Cavity insulation. Building Research Establishment, Watford, 1980.

� �39 Abdou OA. The dynamic thermal performance of masonry wall assemblies of similar thermal resistance. Proceedings of the 8th International Brick�Block Masonry Conference, Berlin, 1991.

� �40 Surface condensation and mould growth in traditionally built dwellings. Digest 297. Building Research Establishment, Wat- ford, 1985.

� �41 Sound insulation: basic principles. Digest 337. Building Re- search Establishment, Watford, 1988.

� �42 Sound insulation of separating walls and floors. Digest 333. Building Research Establishment, Watford, 1988.

� �43 De Vekey RC. The fire performance of insulated cavity walls. Proc Br Masonry Soc 1998;8:234�9.

� �44 Egan J. Rethinking construction. London: Department of the Environment and the Regions, 1998.

� �45 Hendry AW. Rationalisation of masonry construction. Masonry Ž .Int 1993;7 2 .

� �46 Bau-Erfolg: mauerwerkesysteme. KLB Klimatleichtblock, An- dernach, 1999.

� �47 Berkers WGJ. Building with calcium silicate elements. Proc Br Masonry Soc 1995;7:176�9.

� �48 Fanning A, Hobbs B, Dawood N. Standardisation of brickwork construction: business process re-engineering strategies for conventional brickwork. Proceedings of the 12th International Brick and Block Masonry Conference, Madrid, 2000.

� �49 FRSM Trade brochure. FRACO, ST. Mathias-sur-Richelieu, Quebec, 2000.

� � Ž .50 West HWH. Industrialised building in six parts . I, II Claycraft Ž . Ž . Ž . Ž . Ž . Ž .37 1 & 12 1964, III �VI Claycraft 38 3 , 6 , 10 , 12 1965.

� �51 Knight T. Fast track innovation. Brick Bulletin Autumn, 1995. � �52 On site automation EZ-block automated block-laying system.

Masonry Construction, Addison Ill. July, 2000: 42.