BUILDING AND CONSTRUCTION (BUILDING)
CERTIFICATE IV
NSW TAFE COURSE - 17472
Training Package BCG03
BCGBC4006A
Select, procure and store construction
materials for low-rise projects
TAFE NSW RIVERINA INSTITUTE, ALBURY CAMPUS
Albury Campus , Poole Street, Albury NSW 2640
Ph + 61 2 6058 2800 Fax +61 2 6021 5816
BCGBC4006A
Select, Procure and Store Construction Materials for Low-rise Projects
Contents
Units
1
Factors affecting the performance of building materials
2
Timber & Engineered timber products
3
Mortars, Concrete & concrete products
4
Clay products & stone
5
Plaster, plasterboard, compressed cement products &
insulation
6
Metals & glass
7
Paints & coatings
8
Plastics & adhesives
9
Alternative Materials
Acknowledgement
The composition of these student class notes has been undertaken as to
ensure that the original TAFE OTEN notes (NSW) and any updated
information from the Building Code of Australia 2008 [BCA] (NSW)
provisions, and any other documents, literature and referrals including
Australian Standards, are fully explained and are reflected within these
notes.
This document is acknowledged as a personal revamp of the above
mention information as to provide concise and as current information as
possible to the students. I thank my fellow Riverina Institute Building and
Construction Teachers for their assistance for some of this information.
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UNIT 1
Factors affecting
the selection of
building materials
Learning Outcomes:
Identify and evaluate the properties of building
2
•
The suitability of materials commonly used in the region for low-rise buildings
is identified for a given building system.
•
The properties of materials, their quality and the compatibility and noncompatibility of different materials are identified.
•
The environmental impacts of different materials are identified
•
The impact of allowable tolerances on the conversion of naturally occurring
materials is identified.
•
The tolerances for installing and assembling materials are identified and
checked in regard to the nature of the work being performed and the
requirements of the Australian standards.
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Factors affecting the selection of building materials
In this section you will learn about the characteristics and quality
standards of building materials commonly used in residential scale
buildings. This knowledge will help you to select the most appropriate
materials for your work.
We will examine a wide range of building materials: timber and timber
products, concrete and concrete products, clay and stone, mortars,
plaster and plasterboard, metals and glass, paint and coatings, plastics
and adhesives and alternative materials. Before we examine each of
these materials you will need to know what affects the performance of
building materials in general. This is what you will study in this first
section.
There is a wide range of possible building materials available for our use
and the performance of these materials has an impact on the cost,
aesthetics and function of the building.
A well designed, economical building takes the following factors into
account:
• the properties and behaviour of building materials
• the initial and long-term costs
• the effects on the environment
• how the materials interact with each other.
•
The traditional building materials such as stone, timber and clay have
been used for centuries and the performance of these materials has
changed little over time.
However, with the advent of modern manufacturing processes, the list of
materials available to builders today is far longer than at any other time
in the history of construction.
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With the introduction of cement and concrete, steel, aluminium and
products from the chemical industry, the traditional range has increased
dramatically. Builders today must be aware of many factors affecting the
use of these materials and how they have an affect on the environment.
Table 1, below, lists materials commonly used in residential construction.
While not absolutely complete, it does illustrate the potential variety of
materials available to us.
Material
Adhesives
and jointfillers
Cement
Clay
Cloth
Glass
Grasses
Gypsum
Metals
4
Products and uses
for gluing, sealing and filling cracks and joints
for concrete slabs and other elements; concrete
blocks; cement render on walls; compressed
cement sheets
for bricks and tiles; mud bricks; vitrified clay
(sewer and stormwater) pipes
canvas (for awnings etc)
for windows; skylights; doors; fibreglass
insulation
straw (in mud bricks and rammed earth walls and
in bales in straw bale constructions)
for plaster on walls; grout between tiles;
plasterboard
timber fasteners (such as nails, screws, bolts,
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Paper
Plastics
Soil
Stone
Timber
Select, Procure and Store Construction Materials for Low-rise Projects
brackets, gang-nail plates)
steel/iron (such as zincalume profile sheet steel,
tanks, gutters, downpipes, wire and wire mesh)
steel (beams, columns, brackets and reinforcing)
copper (pipes and electrical wiring)
brass (taps, screws, door and window fittings)
aluminium (door and window frames, gutters,
downpipes)
wallpaper; tar paper
for electrical fittings; paints; wastes, water and
sewerage pipes; plastic sheets (as moisture
barriers)
rammed earth walls and floors
building blocks and slabs; slates; aggregate in
concrete; pebble finish on concrete
floors; doors; window frames; weatherboards;
roof framing; wall framing; shingles; shakes
(similar to shingles, but split not sawn)
Table 1: Materials and their uses in residential construction
We will now look at most of the materials listed above.
Principal factors that affect the selection of materials
The selection of materials is affected by a range of factors including:
• economic
• physical
Let’s examine these factors in detail.
Economic factors
Energy content
Building materials are sometimes described as having a certain ‘energy
content’. This refers to the cost of their production.
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Stone (for concrete aggregate), timber or sand are materials having a
‘low energy content’; that is, they do not require a primary manufacturing
process. Some materials, which are by-products of other industrial
processes (eg wood particles, blast furnace slag and pulverised ash),
also have a low energy content.
Materials with a low energy content are cheaper because energy has not
been used in their production.
Other materials require energy in their production, and therefore have a
‘high energy content’. These include, for example, glass, bricks, plastics,
metals and cement. This adds to their cost, and if local supplies of the
raw materials are exhausted or unavailable, then purchase and transport
costs are also added to the overall cost.
Labour and material costs
The initial cost of building will depend almost entirely on the costs of
materials and on the labour costs. The cost breakdown for housing
construction is roughly:
• 5% fee and charges
• 50% materials
• 45% labour
The choice of materials should not depend only on the purchase and
installation cost, but also on the cost of repair, maintenance and
replacement of short life-span products. Less durable materials may be
cheap to buy but repair or replacement costs are usually high.
Cheap materials usually lower the value of a building, whereas more
durable materials, such as stone and brick, mellow with age and give the
structure a more aesthetic appearance.
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Conservation of resources
Most world resources of metals, rainforest timber, fossil fuel and
limestone are non-renewable and limited.
It is therefore important for us as consumers not only to be aware of
those resources which are threatened or have bad effects on the
environment, but also to use those which are, with management, safe
both to our health and to the environment as a whole. Where possible
we should use renewable resources, such as timber from re-planting
programs.
It is also important that world fuel energy is not wasted by unnecessary
processing and transportation. As well as being environmentally
desirable, these savings mean cheaper materials.
Physical properties
Materials have different characteristics, or properties.
These properties are affected by physical, chemical and biological
factors.
Here we will be looking at the following properties:
• density and specific gravity
• strength
• electrical conductivity
• thermal conductivity and capacity
• moisture absorption
• acoustics
Properties that relate specifically to certain building materials will be
looked at in later sections where the particular building material is dealt
with at length (eg optical properties will be dealt with in the section on
glass).
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Density and specific gravity
Different substances have different densities. Iron is much denser than
aluminium which is why a piece of aluminium is much lighter than a piece
of iron of the same size. Ice floats in water because the ice is less dense
than the water. Density is measured by specific gravity.
Specific gravity is the ratio of the mass of a given volume of a liquid or
solid to that of the same volume of water. The density of pure water is
taken as 1 at 4° C.
Strength
A structure (eg a beam or a bridge) must be able to safely support its
own weight plus the load it carries without distortion. Distortion will
reduce the efficiency of the structure or make it break or look
unattractive.
A structure can be made much stronger without increasing its weight, by
being made in a different shape. Structures have greater strength when
used in different ways. For example, in Figure 1 on the next page, the
steel beam on the left (A) is much stronger than either of the other steel
beams to its right (B or C), even though they all contain the same
amount of steel.
Figure 1: Different types of steel sections
Some materials strongly resist being squashed. They are said to have
compressive strength. Concrete, stone and brick are such materials.
Other materials, such as steel, are strong under tension and will resist
being stretched.
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Concrete cracks easily when stretched. It has low tensile strength. The
behaviour of concrete under pressure is illustrated in Figure 2.
Figure 2: The concrete beam cracks on the tension face (underside)
By using steel reinforcing in concrete, we combine the tensile strength of
steel with the compressive strength of concrete, resulting in a product
that is strong in tension as well as being strong in compression (refer to
Figure 3).
Figure 3: Adding steel in the lower half of beam limits cracking
A piece of 25 mm wide galvanised steel strap, which is often used in
bracing timber frames, is very difficult to stretch, but crumples easily
when compressed lengthways. It has high tensile strength and low
compressive strength.
Materials that are undergoing force are said to be stressed, and their
change in shape is called strain. An elastic material is one which will
recover its original shape when the stress is removed. A steel spring is
elastic. A piece of chewing gum is not very elastic.
The response of materials to stress will depend on:
• how stress is applied to them
• whether the stress is continuous (eg a load-bearing arch)
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• whether the material is compressed, stretched or twisted
• whether it is affected by moisture or temperature
Revision
Undertake the following Questions
1.
Why does ice float in water?
……………………………………………………………………………
……………………………………………………………………………
……………………………………………………………………………
2.
What are we measuring when we compare things with the density
of pure water at 40C
……………………………………………………………………………
……………………………………………………………………………
……………………………………………………………………………
……………………………………………………………………………
3.
What is the advantage in laying a timber beam across two end
supports as compared to laying the same beam flat across the
same supports?
……………………………………………………………………………
……………………………………………………………………………
……………………………………………………………………………
4.
10
Pair the following statements with the appropriate term:
a). A material’s capacity to resist being squashed
i)
elasticity
b). A materials capacity to resist being stretched
ii)
stress
c). A material’s capacity to return to its own shape
iii)
tensile strength
d). Force applied to a material
iv)
strain
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e). A change in material’s shape as a result of undergoing force
v)
compressive
strength
5.
List & explain the three different types of stress that may affect the
performance of a material?
……………………………………………………………………………
……………………………………………………………………………
……………………………………………………………………………
……………………………………………………………………………
……………………………………………………………………………
…………………………………………………………………
Moisture absorption
Some very porous materials will absorb moisture more readily than
others. However, most materials may take up moisture from the air, from
the ground (eg through poor dampcourses), from damaged roofs or
gutters, or by condensation.
Condensation from moisture in the air will form on surfaces colder than
the air. In the past, traditional building methods allowed water vapour to
travel out of the building. Nowadays, however, condensation often
becomes trapped on the inner surface of water-tight materials (eg flatroof coverings, metal and glass wall-cladding, foil insulation). This can
be prevented by the correct use of vapour barriers (materials which are
designed to prevent surface condensation by being placed on the warm
side of walls or ceilings in such a way that there is no gap in them).
Electrical conductivity
Materials that easily carry electricity through them are said to be
conductors. Materials that do not are non-conductors. For example,
most metals are good conductors and most plastics are not. This is why
electrical wiring is copper and the protective sheathing is plastic.
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Thermal conductivity and capacity
The thermal properties of a material are concerned with how a material
reacts to changes in temperature. The thermal properties include heat
expansion or contraction, insulation, heat storing ability, cooling, and
reaction to frost, snow and ice.
Thermal conductivity is a measure of how fast heat travels through
materials. This rate may be affected by density, temperature, porosity
and moisture content.
For example, a building material that has a moisture content of 20% will
lose two to three times more heat than when it is dry.
Thermal capacity is the ability of a substance to store heat. A brick or a
stone wall, for example, will heat up slowly, hold the heat and lose it
slowly as the outside temperature drops. A thin, light wall, on the other
hand, heats and cools quickly and does not provide a buffer to the
climate. Underground houses provide an ideal thermal situation because
the surrounding soil slowly heats up during summer and is warmest in
winter; it then gradually loses heat again so that, by summer, the soil
temperature is cooler than the outside air.
The choice of materials of various thermal capacities will depend on the
type of climate and the use to which the building is put.
Acoustics
Insulation from noise can be achieved by the use of dense materials, by
avoiding openings directly onto noisy areas and by avoiding direct paths.
For example, a hall with a bend leading from a noisy machine shop to
the workers’ tea room or a hall with lobbies or double doors would both
reduce noise.
Some porous materials are used for modifying the acoustics in a room
but sound can only be prevented from travelling from one space to
another by the use of dense materials or a vacuum.
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On the inside of a building, double-glazed windows, heavy curtains, wallhangings and carpet all help absorb noise. On the outside, walls,
fences, hedges, trees and bushes may be used to reduce traffic or
industrial noise.
Revision
Undertake the following Questions
1.
What is an electrical conductor?
……………………………………………………………………………
……………………………………………………………………………
2.
If thermal conductively is a measure of how fast heat travels
through materials, name four things that can affect it.
……………………………………………………………………………
……………………………………………………………………………
……………………………………………………………………………
……………………………………………………………………………
3.
How would the thermal features of a brick construction compare
with those of a timber frame construction?
……………………………………………………………………………
……………………………………………………………………………
……………………………………………………………………………
……………………………………………………………………………
4.
In what way does an underground house provide an ideal thermal
situation?
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……………………………………………………………………………
……………………………………………………………………………
……………………………………………………………………………
……………………………………………………………………………
……………………………………………………………………………
5.
How can surface condensation on walls and ceilings be prevented?
……………………………………………………………………………
……………………………………………………………………………
……………………………………………………………………………
……………………………………………………………………………
6.
List six ways of modifying unwanted noise.
……………………………………………………………………………
……………………………………………………………………………
……………………………………………………………………………
……………………………………………………………………………
……………………………………………………………………………
…………………………………………………………………………….
External factors that affect the performance of materials
Building materials undergo changes over time and the following factors
affect their performance:
• movement caused by applied loads
• movement caused by temperature
• movement caused by moisture
Movements may be substantial and result in considerable stresses. If
these stresses are greater than the strength of the material then,
obviously, cracks or buckling will result.
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Movement caused by applied loads
These loads may occur by design or by accident. They may be caused
by error in structural design or from overloading.
Movement caused by temperature
Most substances are affected by temperature changes, expanding when
heated and contracting when cool, but some are affected more than
others. This is called thermal movement. Figure 4 shows a comparison
of the relative changes due to temperature in a number of materials.
Dark coloured materials set into light coloured ones
Dark coloured materials, when exposed to the sun, can heat up and
expand greatly, causing cracks in the material in which they are set. Or
else the dark materials may themselves crack or buckle. For this reason,
roof surfaces (such as sheet metal) are best finished with a solar heatreflecting surface or paint. Coloured glass in a sunny wall must be able
to move freely, as it will expand and contract with temperature changes.
If the glass is set between metal screws or beading that prevents this
movement, it will crack. Putty or silicone caulk allows such movement.
Long walls
Long walls must be allowed to expand in every direction. Movement
joints are placed at recommended intervals. A long wall butted up to
buildings at each end may distort, causing cracks. The wall could also
fail at weak points, such as over archways or doorways. If the wall itself
does not give under the pressure, then it could cause cracks or bulges in
the walls that it is butted up against at each end.
Polythene
Acrylics
Timber across the grain
Zinc
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Lead
Aluminium
Brass
Copper
Stainless steel
Gypsum plaster
Concretes
Mild steel
Glass
Building stones
Plywood
Bricks of fired clay
Mortars
Asbestos cement
Timber along the grain
LOW
Figure 4: Relative changes in the sizes of
various materials due to thermal movement
Movement caused by moisture
A change in the moisture content of most materials will result in
deformation: they will swell when wet and shrink when dry. These
changes, called moisture movements, can result in warped, twisted,
shrunk or cracked items.
Properties of materials that affect the performance
of materials
Building materials undergo changes over time and the following factors
affect their performance:
• durability of the materials
• fire resistance
• compatibility of different materials
Durability
Since all materials deteriorate over time to some extent, we should be
able to anticipate these changes and take them into account when
designing a structure, whether it is a house, a shed or a cupboard. We
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should foresee normal wear and tear, as well as the occasional very
heavy stress caused by storms, fire, flood or burglary for example.
Durability will be different for different exposures. A coat of paint will last
for many years inside a cupboard or less than a year in a sunny exposed
position in a heavily polluted industrial area. We are all aware of the
effect of salt spray on a car. Buildings are similarly affected, though it is
not always so obvious.
Direct and indirect causes of deterioration include:
• corrosion of metals
• sunlight
• biological agencies
• water and frost
• salt crystallisation
• chemical action
• loss of volatiles
• abrasion and impact (wear)
• vibration
• fire
Corrosion of metals
Deterioration of specific metals will be examined later, in the section on
metals. The effects of metal deterioration on surrounding materials can
be significant, and will be looked at in the context of these materials
when they are dealt with in later sections.
Sunlight
Sunlight causes drying and cracking of timbers. It also fades colours and
pigments and its heating of dark coloured materials can greatly speed up
their breakdown.
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Ultraviolet radiation causes breakdown of clear finishes, stains, paints,
rubber, some plastics and polythenes, tars and bitumen, fabrics and
canvas.
Metals, bricks and stones are largely unaffected by sunlight.
Biological agencies
The destruction of timber by termites, borers and fungi will be discussed
in the section on timber.
Certain bacteria in the soil break down sulphur chemicals which cause
corrosion of metals such as iron, steel and lead.
Burrowing animals or birds making nests can tunnel foundations,
undermining footings; they can also excavate loose unsound material
allowing rain in or weakening supports.
Tree roots and vines growing in cracks exert a very strong and
destructive force, expanding and extending cracks in masonry, pipes,
concrete or timber. They also hold moisture, encouraging the growth of
moulds and fungi, and the uneven drying of brickwork (which causes
uneven movements within the wall).
Water and frost
Care should be taken in the selection of materials for use in damp areas
since some building materials react less well in such situations than
others. For instance, limestone and marble slowly dissolve in water.
Timber, chipboards, hardboards and other similar wood products lose
some of their strength, and many flooring materials are less hardwearing when wet.
Water can encourage fungal attack and certain destructive chemical
reactions. Repeated wetting and drying causes surface crazing and
cracking of timbers. Water also often carries destructive acids, salts and
other soluble chemicals.
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Salt crystallisation
Salts that are dissolved in water can come from the sea, the ground and
from some building materials. As moisture evaporates from a surface,
the salts are left behind in the form of powder or crystals, called
efflorescence. Sometimes this is just an unattractive coating, usually
white, but sometimes yellow, green or brown. However, it can be
destructive if allowed to persist for a long time.
Salts crystallising on the surface of a porous material can cause gradual
erosion or flaking. This surface deterioration, called fretting or spalling,
often occurs in soft sandstones, bricks (such as sandstocks) or in mortar
layers in masonry. When moisture rises in the walls of a building these
salts cause paint to bubble and peel. Fixing this problem can involve
costly installation of dampcourses and removal of all affected plaster or
render from the walls.
Chemical action
Chemical reactions in materials can cause swelling, shrinking, weakness
or damaged appearance. This can be due to chemical changes within
the material itself, or changes brought on by attack from outside
chemicals. Heat and moisture aid most reactions.
The presence of aggressive gases, in the air or in factories or dissolved
in rainwater, can mean that some materials may need special protection,
or that other more suitable materials should be used instead.
Groundwater, industrial wastes, soil, ash and wet clays are some of the
substances that can produce soluble sulphates which attack cement
products and metals.
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Loss of volatiles
Volatiles are liquids and gases. Plastics, paints, varnishes, finishes,
mastic, rubber, tar and bitumen shrink and become brittle when their
volatiles are lost.
Abrasion and impact
In situations of abnormal impact or abrasion, suitable materials and
finishes need to be chosen. For example, a concrete path or floor that
will take heavy traffic requires correct concreting techniques to be
followed so as to produce a hard, durable surface.
Vibration
Vibration caused by proximity to machinery or heavy vehicular traffic can
cause problems in light constructions and in those with brittle materials.
Revision
Undertake the following Questions
1.
List three things that can cause deformation of a material or
building component.
……………………………………………………………………………
……………………………………………………………………………
……………………………………………………………………………
2.
Why does dark glass crack when set in a wall in a sunny location
and explain how you would stop it cracking?
……………………………………………………………………………
……………………………………………………………………………
……………………………………………………………………………
……………………………………………………………………………
……………………………………………………………………………
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3.
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How can deformation caused by temperature changes be
prevented in long walls?
……………………………………………………………………………
……………………………………………………………………………
……………………………………………………………………………
……………………………………………………………………………
4.
Give an example of each of the following types of deterioration:
Sunlight:
…………………………………………………………………………..
……………………………………………………………………………
Biological agents:
……………………………………………………………………………
……………………………………………………………………………
Water:
……………………………………………………………………………
……………………………………………………………………………
5.
Select the correct answer for each of the following statements.
a). Efflorescence is related to…………..
(i).
Abrasion
(ii).
Salt
(iii). Rain
(iv). Incorrect mortar
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b). Efflorescence can affect………….
(i).
Soft brick or sandstone
(ii).
Hardbrick or granite
(iii). Timber
(iv). Glass
6.
Are most chemical reactions inhibited or aided by heat and
moisture?
……………………………………………………………………………
……………………………………………………………………………
7.
What precaution should be taken to protect a floor from abnormal
abrasion and impact?
……………………………………………………………………………
……………………………………………………………………………
……………………………………………………………………………
Fire resistance
Fire is usually the fastest, most destructive and dangerous way in which
a building can be damaged or destroyed. It is a very important
consideration for both city and country dwellers.
Government bodies test materials and publish regulations and codes
which are implemented by local councils concerned about fire hazards in
public or private buildings.
Fire hazard indices (published by the Experimental Building Station as
‘Notes on the Science of Building’, Nos 66, 98, 136, 137, 142) are lists
based on extensive experiments on structures and materials.
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NSB 66 Fire aspects of combustible wallboards and finishes
NSB 98 Lightweight fire resisting construction
NSB 136 Fire doors, fire shutters and fire windows
NSB 137 Fire hazards of furniture and furnishings
NSB 142 Fire hazards in the home
Fire resistance ratings are also determined by laboratory tests. The
ratings indicate the time for a material to fail in a burning building. They
are expressed as hours and minutes.
Fire is a chemical reaction which needs fuel, heat and oxygen. Moist
solids and liquids give off vapour when they are heated and it is this
which burns as a flame. Solids can only burn at or near the surface.
Open-textured materials burn more quickly because they have more
surface area, while fine dusts (eg from coal, wood, flour, aluminium and
many plastics) become explosive when suspended in air.
In a fire, materials may melt, burn, weaken, expand, shrink or crack.
Flame and building collapse cause injury and death. However, smoke
and gases are equally dangerous (even when flames are not present),
causing confusion, unconsciousness, panic, loss of vision and
asphyxiation.
Solids can smoulder in a confined space for a long time on only one-third
of their normal oxygen supply and then, on the sudden entry of air (a
door being opened, for example), burst explosively into flame. This is
called flash-over.
Combustibility
Materials that ignite, that give off flammable gases or that show
considerable self-heating when exposed to a set heat in a furnace, are
called combustible.
Non-combustible materials, on the other hand, do not feed the fire, and
flame does not spread over them. Non-combustibility does not mean fire
resistance. Table 2 lists some combustible and non-combustible
materials.
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Non-combustible materials (such as steel) may expand and disturb
attached structures, or lose strength and collapse. Other noncombustible materials may spall (flake) and shrink or crack. On the other
hand, some combustible materials (such as timber) can often provide a
useful degree of fire resistance.
Combustible
Timber
Cork
Hardboard
Chipboard
Wood laminates
Gypsum plaster board
Bitumen felts
All plastics and rubbers
Glass fibre/mineral wool with
combustible bonding agents
Non-combustible
Fibrous cement products
Compressed cement sheets
Bricks
Stones
Concretes
Metals
Glass fibre and mineral wool
containing less than 4–5%
bonding agent
Table 2: Some combustible and non-combustible materials
Fire resistance is expressed as the amount of time in hours and minutes
a component survives a fire test of set temperature before it can no
longer perform its function. It is considered to fail the test when any of
the following occur:
• It collapses.
• It forms holes or cracks through which flame can pass.
• It gets hot enough to ignite other combustible materials it is in
contact with and which the fire hasn’t yet reached.
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How certain materials behave in fire
Timber
Timber easily ignites at about 221–298°C. However, some timber
(particularly large pieces, at least 100 by 75 mm in section or larger) are
resistant to the fire, once the surface has been charred. Many Australian
hardwoods have this characteristic and, in fact, have proved to be more
fire resistant in buildings than steel. However, all timbers do burn readily
if temperatures stay high enough. Therefore, timber buildings are not
classified as fire resistant.
Timber has good thermal insulation, preventing materials not in contact
with the fire from heating up to extreme temperatures. When hot, timber
does not expand in length (unlike steel) and neither does it markedly lose
strength.
Laminated timber structures glued with synthetic resins have similar fire
resistance to solid timber, although resistance will vary according to the
type of timbers and glues.
Stone
Stone blocks and slabs are usually satisfactory in fires, but overhanging
features and lintels are liable to fail. Free quartz (eg in granites)
explodes suddenly at 575°C and should not be present in any stone that
is required to be fire resistant. Sandstones behave better than granite,
but in drying they may shrink and crack, with 30–50% loss of strength.
Plastics
Although many plastics are made in fire-retardant grades, all are
combustible and some give off large quantities of toxic smoke. PVC
(polyvinyl chloride) melts at fairly low temperatures, and most
thermoplastics (plastics that can be heated and shaped) char above
400°C and burn at 700–900°C.
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Clay products
Most clay products perform well in fires, having been made at kiln
temperatures higher than most fires reach.
Brickwork failure is often caused by expansion of enclosed or adjoining
steelwork.
Concrete
Ordinary Portland cement concrete disintegrates at 400–500°C.
However, how the concrete performs depends very much on the
presence of reinforcement and the type of aggregate it contains.
Metals
Metals used in building are non-combustible, but they lose strength when
heated. Aluminium, lead and zinc melt in building fire temperatures. As
previously mentioned, the expansion of the hot metal can cause
problems. Also, the high thermal conductivity of metals means that the
temperature of surfaces remote from a source of heat will approach the
temperatures near the fire, causing fires to spread.
Steel
Mild steel behaves in an interesting way when heated. Up to 250°C, it
gains strength, then gradually returns to normal strength by 400°C. After
that, it rapidly weakens so that, at 550°C (referred to as the critical
temperature), it begins to fail.
Generally, structural steelwork must be protected with fire-resistant
encasements, such as concrete or brickwork.
Glass
Although glass is non-combustible, it readily transmits heat and often
shatters unpredictably at an early stage in a fire. Toughened glass is not
fire-resistant.
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Glass fibre and rockwool
Resin-bonded glass fibres are combustible. Glass fibres themselves
melt at about 600°C.
Fibrous cement
This material tends to shatter when heated, sometimes explosively. It
does not contribute to making a fire-resistant structure.
Paints
Generally, paint films are combustible and may help spread flame over
surfaces. However, as they are thin, they only contribute a small amount
to the fire load. When applied to combustible materials, certain paints
can reduce the spread of flames. They delay but never prevent the
spread of flame.
Revision
Undertake the following Questions
1.
Fire resistance ratings are lists
(a) Produced by insurance companies
(b) Showing the costs of fires on certain materials
(c) Indicating how long a material takes to fail in burning buildings
(d) Showing which towns have a good fire-fighting record.
2.
Fire is a chemical reaction, needing what three (3) things?
……………………………………………………………………………
……………………………………………………………………………
3.
Name four (4) ways that substances may be affected by fire.
……………………………………………………………………………
……………………………………………………………………………
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4.
Select, Procure and Store Construction Materials for Low-rise Projects
What specific dangers to people are posed by smoke and gases in
a fire in which no flame is present?
……………………………………………………………………………
……………………………………………………………………………
5.
What is the difference between a non-combustible item and a fireresistant item?
……………………………………………………………………………
……………………………………………………………………………
……………………………………………………………………………
6.
List five (5) combustible and five (5) non-combustible materials.
……………………………………………………………………………
……………………………………………………………………………
……………………………………………………………………………
……………………………………………………………………………
7.
Which materials display good thermal insulation in a fire?
……………………………………………………………………………
……………………………………………………………………………
8.
Name three (3) metals that will melt at building fire temperatures.
……………………………………………………………………………
……………………………………………………………………………
9.
Why should structural steel be protected with fire-resistant
encasements when it does not burn?
……………………………………………………………………………
……………………………………………………………………………
……………………………………………………………………………
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Compatibility of materials
The large range of new materials on the market today, many of which
are chemically based, plus widespread pollution, has led to new
chemical and physical problems with materials. A material may break
down many times faster than normal in the presence of another
particular substance.
Problems do not always show up until a product has been on the market
for a number of years. Incompatibility of building materials can be
grouped roughly under the following headings:
• corrosion of metals
• stains and discolouring effects
• problems with surface finishes
• chemical reaction between materials
Corrosion of metals
Galvanic reactions: These occur between metals that have different
levels of electro negativity. This is often seen as corrosion of one metal
or a deposition of metal scale on the other metal. Offcuts or filings of
metals left around in moisture can cause rapid destruction of nearby
metal building components. Some common galvanic reactions are listed
below.
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GALVANIC SERIES OF METALS
Anodic End
When two metals are in
contact, the less noble will be
corroded, while the more noble
one is protected.
The further the two metals are
apart on the chart, the more
reactive they are to each
other.
Cathodic End
CORRODED
Magnesium Alloys
Zinc
Commercially pure Aluminium
Cadium
High-strength Aluminium Alloys
Iron and Steel
Tin
Brasses (Copper-Zinc Alloys)
Copper
Bronzes (Copper-Tin Alloys)
Monel Metal
Silver Solder
Nickel (passive)
Stainless Steel (passive)
Silver
Gold
Platinum
PROTECTED
• Lead used with zinc or aluminium promotes corrosion. Therefore,
metal roof-flashings need to be carefully chosen.
• Steel screws or nails should not be used with aluminium or zinc
roofing, unless they are zinc or cadmium coated.
• Copper should not touch or drain onto zinc, aluminium, zincalume or
galvanised materials.
• Lead-based or graphite paints should not be used on aluminium.
Water-metal corrosion: Most iron or steel rusts on contact with air and
moisture. Protection is provided by galvanising or coating with zinc,
aluminium or PVC plastic.
Galvanised pipes: For water supplies these are reasonably durable
where water is hard or not acidic. But if water is low to moderately hard,
corrosion occurs quite rapidly at joints with brass or other copper alloys.
This can be reduced with effective diameter pipes, and eliminated with
plastic connectors.
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As heat speeds up corrosion, different metals should not be mixed in hot
water systems. Copper and brass are permanently resistant to water.
Aluminium: This becomes encrusted in coastal atmospheres. Mortar,
cement or concrete pit the surface of aluminium if splashed on it.
Industrial atmospheres: These are usually acidic and corrode all metals.
Stains and discolouring effects
Copper: Water dripping off copper causes green stains.
Rust: Water running off exposed iron or steel will stain surrounding
surfaces.
Eucalypt timbers: When wet, many eucalypt timbers produce brown
stains on masonry.
Efflorescent salts: When these move through porous brick, stone, mortar
or concrete, they cause surface crusts called efflorescence.
Problems with surface finishes
When finishes won’t stick to the surface they are applied to, it is usually
due to the two being unsuitable for each other. The surface may either
be too smooth or it may be powdery or flaky; or there might be a
chemical incompatibility between the surface and the finish. This will be
dealt with in more detail in the section on paints.
A few special points about surface finishes are:
• Many silicone sealants will not accept paint.
• Acid-resisting grouts (for floor-tiles) cannot be satisfactorily cleaned
from the tile surface.
• Primers, undercoats, finish paints, lacquers, varnishes and stains
should all be used according to manufacturers’ instructions as many
are incompatible with certain materials.
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Chemical reactions between materials
Salt: This is highly corrosive to iron and steel. Porous masonry and
ceramics (such as some stone, brick, terracotta and concrete) can be
severely affected by salt penetration.
Milk: Milk contains lactic acid, which is very destructive to concrete in
dairies and special surface treatment is needed.
Ammonia: Ammonia, present in some adhesives, can damage copper
and brass.
Lead and galvanised steel: These metals will corrode in wet conditions
when in contact with cement mortar or concrete.
Other factors that affect the performance of materials
Building materials undergo changes over time and the following factors
affect their performance:
• testing of materials
• handling and storage of materials
• tolerances
Testing of materials
The testing of materials is carried out by the manufacturer or supplier
before delivery (eg stress testing of timber). Upon delivery, an inspection
should be carried out with respect to the quality and suitability for the
construction situation it is intended.
Concrete is one material which is tested on site (the slump test), and
later laboratory tested for compressive strength at 28 days. Materials
such as paints, adhesives, glass and the like have been developed and
trailed under strict laboratory controls and conform to Australian
Standards.
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You, as the builder or supervisor of a building project, need to be
informed of all the information relating to products being used. Details
such as handling, storage, application, installation and warranties should
be kept in a product file and updated to provide ready access to this
information to avoid warranty problems associated with incorrect
handling and installation.
Handling and storage of materials
Planning for storage and handling of materials on site is an important job
for building staff. Many materials are easily damaged if due care is not
taken in handling, and some can deteriorate if exposed to moisture and
direct sunlight.
Materials should be stored in accordance with manufacturers’
instructions; for example, stacked flat, off the ground, in a dry area or in a
secure area for flammable or toxic materials.
Transportation to the site and unloading arrangements need to be given
careful consideration and appropriate equipment must be organised.
When handling materials on site, safe working practices must be
followed and all OH&S regulations implemented.
Tolerances
All building work in Australia is covered by the Building Code of Australia
and many Australian Standards. These standards have been developed
for most building materials and detail tolerances, application, testing
(if applicable) and method of installation. These tolerances should be
followed and best industry practice adhered to.
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