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For this homework assignment, you need to read the paper entitled “Masonry walls: materials and construction
Actions ” by Emeritus A.W. Hendry and write a summary of the paper in Minimum of 750 words. You need to TYPE your essay in MS Word . Please note that you need to write the summary in your own language and direct copy from the paper without paraphrasing the sentences will be considered plagiarism and will lead to a “ZERO” grade in this assignment.

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 …

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