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Title: Wall

Wall Ceiling Linings
  • In previous units in this subject, building
    materials were divided according to their nature
    of origin (eg clay products). Because both wall
    and ceiling linings and insulation materials can
    comprise any number of different base materials
    or combinations of materials, it seems more
    logical, in this case, to approach this unit
    differentlyaccording to the function which the
    materials perform rather than the nature of the
    raw material.
  • This unit, therefore, is divided into two
    sections the first deals with wall and ceiling
    linings and the second with insulation.

Learning outcomes
  • On completion of this unit, you should be able
  • describe the types of wall and ceiling lining and
    insulation materials most commonly in use in this
  • compare and contrast properties associated with
    the various alternatives
  • recognise suitable applications for the materials

Wall and ceiling linings
  • The terms wall lining and ceiling lining
    refer to the internal wall and ceiling covering
    of the building as opposed to cladding which
    refers to the external wall covering or,
    sometimes, roof covering. Additionally, in this
    unit wall and ceiling lining are defined as being
    distinct from finishes (such as ceramic tiles,
    wallpapers and paints) which are usually applied
    to the wall or ceiling lining.
  • The most common forms of wall lining used in
    Australia are gypsum plasterboard, fibrous
    cement, timber or composite lining boards or
    sheets, plastic coated wall sheeting and solid
  • Timber and composite lining boards and sheets are
    covered in Unit 2. Timber and plastic coated wall
    sheeting is mentioned in Unit 9. In this unit, we
    will concentrate on the other alternatives.

  • The term plaster refers to a jointless and
    usually smooth lining applied to the base wall or
    ceiling structure.
  • Solid plaster was one of the first lining
    materials to be used in buildings. The plaster
    which was made of lime and sand, often with hair
    included, was applied in situ to the masonry wall
    or, in the case of a timber stud wall or ceiling,
    to timber laths which are thin battens fixed
    close together to provide a base.
  • Today, solid or in situ plaster is reserved for
    solid masonry walls timber stud walls are lined
    with plasterboard. However, in situ plastering is
    a wet and messy process and often internal
    masonry is left unplastered (face brickwork, for

  • Plaster comprises a binder, clean sand and fresh
    water, which sets to a comparatively hard, dense
    layer. The properties of the final product depend
    largely on the type and quantity of the binder
  • The binders most commonly used in Australia are
    gypsum plaster, Portland cement and lime (either
    quicklime or hydrated limerefer to Unit 5) or
    organic binders.

Gypsum plaster
  • Calcium sulphate or gypsum plaster can be used
    for undercoats and finishing coats. (Plaster of
    Paris is one type of gypsum plaster.) It is
    derived from naturally occurring gypsum rock
    which has been pulverised and heated to drive off
    most of the chemically combined water, resulting
    in a white, pink or grey powder. When water is
    added to gypsum plaster it sets and hardens into
    a crystalline solid, giving off heat and
    expanding slightly in setting.
  • Two other similar binders are derived from gypsum
    plaster hard wall plasters which provide a
    harder finish and Keenes cement, which is the
    hardest of the gypsum plaster mixes.

Portland cement
  • Portland cement is sometimes used as a binder in
    undercoats and finishing coats where an
    exceptionally hard surface is required. Too rapid
    drying increases the likelihood of cracking, and
    shrinkage must be substantially complete before a
    further coat is applied. Plasters in which limes
    are the only binders are rarely used today as the
    final strength is very low.
  • Lime
  • Workability agents or plasticisers, based on
    non-hydraulic lime or organic materials, are used
    to improve the workability of the mix and
    distribute shrinkage stresses, thus reducing
    visible cracking.

  • Plasters in which limes are the only binders are
    rarely used today as the final strength is very
  • Workability agents or plasticisers, based on
    non-hydraulic lime or organic materials, are used
    to improve the workability of the mix and
    distribute shrinkage stresses, thus reducing
    visible cracking.

  • The process of applying solid plaster to a base
    structure is known as rendering. Solid plasters
    are usually applied in two coats. The undercoat
    is often referred to as the scratch coat and
    the finishing coat as the set coat. If the base
    is particularly smooth and the suction uniform, a
    single coat only may be required alternatively,
    a particularly irregular base may require three
  • In some applications the coats may not be of the
    same composition but it is important that each
    coat be well matured before another coat is
    applied, especially if cement is used. A general
    principle to be followed is that each successive
    coat should be weaker than the preceding one.
  • The choice of a plastering system depends upon
    the base to which the plaster is to be applied,
    the performance of the required finish and the
    texture desired.
  • Cement-sand or cement-lime plasters are
    moisture-resistant plasters, while gypsum-based
    plasters should be used internally in dry
    situations only.
  • Mixes containing Portland cement make the hardest
    plasters, and have the greatest resistance to
    impact damage. Keenes plaster is the hardest of
    the gypsum plasters, while lime plaster is the
    softest. Tables 6.1 and 6.2 indicate suitable
    plaster mixes for two- and three-coat internal

  • Table 6.1 Mixes for undercoats for internal
    two-coat and three-coat work

Finishing coat Undercoats (by volume)
Cement setting 1 cement 4 to 5 sand 0.10 lime
Cement lime sand Gypsum plasters 1 cement 5 to 7 sand 0.10 lime
Gypsum plasters 1 plaster 2 to 3 sand (or 1 3 to 1 4.5 by weight)
1 gypsum plaster 1.5 sand 0.10 lime (or 1 2 by weight, plus lime 5 of weight of plaster)
  • Table 6.2 Mixes for finishing coats for internal

Background or undercoat Finishing coats (by volume)
Brick, block, or concrete 1 cement 4 sand 0.10 lime
Cement sand 1 cement 1 lime 5 sand
Cement lime sand 1 cement 1 to 2 lime 6 to 9 sand
Concrete background Cement lime sand (undercoat) Gypsum plaster 1 lime 0.25 to 4 gypsum plaster
  • Porous bases, such as clay bricks and concrete
    blocks, which have a comparatively high suction
    rarely require much preparation other than raking
    of the joints and the removal of loose material.
  • Smooth, dense materials, such as concrete, have
    little suction and offer no mechanical key and
    are either hacked or else treated with a
    spatter-dish, sand-cement mix, often including a
    PVA adhesive, to provide a key.
  • Rough textured surfaces, such as rough concrete,
    provide a good mechanical key and require little

Fibrous plaster
  • Fibrous plaster is made of gypsum plaster
    reinforced with sisal hemp fibre. Nowadays it has
    been replaced by plasterboard for sheeting
    applications but is still used for the more
    complicated decorative mouldings.
  • Fibrous plaster is dimensionally stable and
    easily decorated but is not satisfactory in moist

Gypsum plasterboard
  • Plasterboard is the most commonly used lining for
    timber-framed construction and brick veneer. It
    comprises a core of gypsum plaster reinforced
    with two outside layers of kraft paper, one on
    each face. Some are available with an aluminium
    foil on the back which improves thermal
    insulation performance.
  • Plasterboards are easily decorated and are
    reasonably tough and strong in normal grades but
    are not satisfactory in damp situations. A
    water-resistant board is available which is
    designed to be used in areas where high humidity
    persists and in wet situations where they are
    protected with tiles or a similar impervious
  • Sizes Sheets are available in a broad range of
    sizes. Thicknesses commonly used in domestic
    applications are 10 mm for walls and 13 mm for
    ceilings. However, a 10 mm thick board is now
    available for ceilings also.
  • Fixing The boards are fixed to the studs or
    ceiling joists by gluing or nailing with special
    flat-headed nails. Boards are available with
    either square or recessed edges, the latter being
    used where a flush surface is required. For a
    flush joint, a strip of perforated reinforcing
    paper is embedded in bedding compound in the
    recess and the area is covered with a topping
    cement (see Figure 6.1).

Figure 6.1 Fixing
General properties of plaster and plasterboards
  • Thermal insulation Plaster linings are
    relatively thin and make a correspondingly small
    contribution to the thermal insulation of a
  • Fire resistance Normal plasters are
    non-combustible, have no spread of flame and do
    not produce smoke. Special fire-rated
    plasterboards are available for applications
    which require a fire rating. Often, the addition
    of a specified thickness of plaster or render on
    internal masonry walls is used to achieve a
    required fire rating according to the Building
    Code of Australia.
  • Sound absorption Ordinary plasters have fairly
    low sound absorption values but special acoustic
    plasters and plasterboards are available.
  • Sound insulation As plaster linings are
    relatively thin, they contribute significant
    sound insulation to lightweight components only.
    However, plaster can improve sound insulation by
    sealing the surface to porous base structures.
  • Hardness In housing, a fairly soft finish may be
    preferred but harder surfaces are often required
    in public buildings and the choice of system
    should take this into account. Metal angles are
    used to protect vulnerable corners and provide a
    line for the plasterer to work.

General properties of plaster and plasterboards
  • Durability Gypsum-based products are not usually
    waterproof and the durability of the finish
    depends largely on the composition of the
  • Texture Smooth-trowelled surfaces comprising
    either neat gypsum or gypsum with admixtures are
    most common but texture can be provided by
    special trowelling or by including sand in the
    finish. Bagged finishes are popular on masonry
    walls. These comprise a thin sand-cement mix
    which is wiped over the wall surface with a piece
    of hessian. The resultant thin coat allows the
    form of the masonry units to show through.
  • Check progress 1

  • Fibrous cement
  • Fibrous cement sheeting has replaced asbestos
    cement as a lining and cladding material due to
    the health hazards associated with materials
    containing asbestos.
  • Composition
  • Fibrous cement is made from a mixture of Portland
    cement, sand, cellulose fibre and water,
    compressed into sheets, boards or other shapes.
  • Sizes
  • Sheets are available in a number of sizes.
    Thicknesses for domestic use are generally as
    follows as lining material for eaves, verandas
    or carports4.5 mm or 6 mm sheet for internal
    wall and ceiling linings6 mm compressed fibrous
    cement for wet area floors is 15 mm or 18 mm

  • Sheets can be glued or fixed with special
    galvanised flat-head fibrous cement nails to
    timber frames joints can be covered with fibre
    cement cover moulds or PVC sheet holders (see
    Figure 6.3).
  • Figure 6.3 Cover and junction moulds for
    fibrous cement sheets
  • Exposed internal linings can be flush jointed.
    Special recessed-edge sheets are taped with a
    perforated paper reinforcing tape and finished in
    a similar way to plasterboard sheets, with a
    topping cement.

  • Externally, fibrous cement products can be used
    as cladding in the form of boards, sheets or
    shingles. However, internally, because they are
    waterproof, fibrous cement sheets are used
    primarily as a base lining for other finishes
    (such as tiles) in wet areas. Compressed fibrous
    cement sheeting is also used as a base floor
    material for ceramic tile floors in wet areas.

General Properties
  • Thermal insulation Fibrous cement sheets are
    relatively thin and make a correspondingly small
    contribution to the thermal insulation of the
  • Fire resistance Fibrous cement products will not
    burn, have a zero spread of flame index and do
    not produce smoke.
  • Sound absorption Unless special acoustic
    material is used, fibrous cement lining
    contributes little to the sound absorption
    characteristics of a room.

General Properties
  • Sound insulation The sheets have a greater
    density than plasterboard but are thinner and
    therefore do not significantly affect sound
  • Hardness Care should be taken during handling
    and storage to prevent edges from chipping since
    the material is particularly brittle. When
    painted or otherwise finished, however, a hard
    surface finish can be obtained.
  • Durability Fibrous cement sheets are unaffected
    by sunlight, moisture or termites and should not
    split or rot. Hence its suitability for external
    and wet area applications.
  • Check progress 2

Thermal insulation
  • The question of thermal insulation really forms
    part of the problem of energy efficient design of
    the building as a whole, which includes
    consideration of the following points
  • orientation of the building to maximise the use
    of solar energy (see Figure 6.4)
  • location in relation to summer breezes (see
    Figure 6.5)
  • protection from winter winds (see Figure 6.6)
  • location and treatment of windows (see Figure
  • use of wide eaves or pergolas which shade windows
    and walls from summer sun but allow entry of
    winter sun (see Figure 6.8)
  • use of solar energy in the design to heat floors
    or walls (see Figure 6.9)
  • interior planning (see Figure 6.10)
  • prevention of heat loss through unnecessary gaps
    (see Figure 6.11)
  • design of floors (see Figure 6.12)
  • the colour of the exterior of the house.

Figure 6.4 Paths of the sun in winter and summer
Figure 6.5 Location in relation to summer breezes
Figure 6.6 Protection from winter winds
Figure 6.8 The use of wide eaves or pergolas
Figure 6.10 Interior planning
Thermal insulation
  • Thermal insulation can assist by improving the
    thermal efficiency of the structural components
    of the house by reducing heat loss or gain
    through the major surfaces, such as the walls and

Heat transfer
  • Heat is transferred by
  • conductionheat is led from the side of the
    material at a higher temperature to the side at a
    lower temperature
  • convectionwhen air is heated it expands and
    begins to circulate and heat up colder surfaces
    by losing some of its heat to them
  • radiationwhen air comes in contact with a warm
    object, heat is transferred to the atmosphere.

Thermal resistance
  • A materials ability to resist the flow of heat
    is called its thermal resistance or R-value.
    The higher the R-value of a material, the greater
    its ability to resist the flow of heat.
  • The Energy Authority of NSW provides data on
    recommended R-values for different areas in NSW.
    For instance, if you live in Coffs Harbour the
    recommended minimum level of thermal insulation
    is R1.5 but if you live in Cooma, which is
    colder, the recommended minimum level is R3.0
    (see Figure 6.13).
  • The heat flow through a wall or ceiling is not
    reduced in direct proportion to the R-value of
    any insulation added above the recommended level
    in fact the extra benefit to be gained diminishes
    fairly rapidly beyond this level. Thus, there is
    not much point in installing insulation to a
    value beyond the recommended R-value for your

Types of Insulation
  • Thermal Insulation
  • This type of insulation uses the heat-reflective
    properties of aluminium foil which prevents heat
    transfer by radiation. The following types are
  • Foil laminated to reinforcing membranes, supplied
    in rolls of varying widths. This is used for roof
    sarking and wall sheathing.
  • Laminated foil layers separated by partition
    strips. When the foil is installed over ceiling
    joists the partition strips separate the two
    layers and provide an additional air space to
    increase the effectiveness by decreasing
  • Foil laminated to bulk insulation.
  • Foil-backed plasterboard.
  • Solar reflective film which can be applied
    directly to glass panes.
  • Metal reflective-treated fabrics for blinds,
    curtains and so on.

Bulk Insulation
  • This is normally a cellular material with
    entrapped air bubbles which slow down heat
    transfer by conduction. Several forms are

Batts and blankets
  • Insulation batts and blankets are available in
    the following materials
  • Mineral wool (fibreglass or rockwool),
    manufactured from inorganic raw materials that
    are melted at above 1000C and spun into fibres
    which are then bonded together to form flexible
  • Urethane foam sheet, made from foamed
  • Expanded polystyrene sheet (EPS), made from
    foamed polystyrene.

Loose fill
  • Cellulose fibre, manufactured from waste paper.
  • Exfoliated vermiculite, manufactured from a
    micaceous material.
  • Mineral wool, manufactured as explained above.

In situ foam
  • Urea formaldehyde is pumped in as a mixture of
    chemicals using special equipment. The mixture
    foams up in situ and forms a rigid foam filled
  • Urethane foam is pumped as fluid foam into the
    space where it sets chemically to form a rigid
  • Expanded polystyrene beads are mixed on site with
    a bonding agent and injected into the cavity.

Structural and decorative insulation
  • This type of insulation comprises a complete wall
    or ceiling lining system combining thermal
    insulation and often acoustic modification with a
    decorative lining. Several forms are available
  • Fibreglass panels laminated with decorative
  • Wood wool panelsdecorative boards made from wood
    straw bonded with a cement-like adhesive.
  • Compressed straw panels, manufactured from pine
    or straw fibres which are compressed and bonded
  • Expanded polystyrene, as above with decorative

General properties of insulation materials
  • Thermal performance
  • The type and thickness of the insulation is
    selected according to the required R-value and
    the application. Reflective foil as insulation in
    horizontal applications should be laid face down
    as settling dust renders the upper face
    ineffective. The R-value should be marked on the
    product and manufacturers product information
    should comply with SAA Standards and Test
  • Acoustics
  • Some insulation will also contribute to the
    acoustic performance of the room, especially in
    the case of some of the decorative panels.
  • Fire resistance
  • Some insulation materials are combustible.
    Urethane foam, expanded polystyrene and cellulose
    fibre insulation must contain fire-retardant
    chemicals. Combustible insulation should be
    covered with an appropriate non-combustible
    lining such as gypsum plasterboard.

General properties of insulation materials
  • Safety
  • Most bulk insulation materials should be handled
    with care to avoid dust formation. Gloves and
    long clothes should be worn when installing
    fibreglass to avoid contact with glass fibres,
    which may irritate the skin. In all cases it is
    advisable to wear a mask covering the mouth and
    the nose.
  • Suitability
  • The type of construction will limit your choice
    of insulation system. For instance, loose-fill
    insulation is generally only suitable on flat
    surfaces. In situ insulation may make access to
    the roof space extremely difficult. Loose-fill
    insulation is good for difficult corners.

Where to insulate
  • Because heat rises, most heat loss occurs through
    the ceiling. Figure 6.14 illustrates the
    proportion of heat loss through
  • (Note that the figures given have been calculated
    specifically for the Canberra region and may not
    apply to other areas although the general pattern
    these figures reveal would apply for this type of
    construction elsewhere.)

Figure 6.14 Heat loss through a building
Where to insulate
  • Although the percentage figure for heat loss
    through the walls is the highest, in terms of
    unit area the diagram suggests that (for this
    type of construction) the greatest heat losses
    are in fact through the ceiling and, next, the
    floor. Consequently, the first place to consider
    insulating is above the ceiling (see Figure 6.15).

Figure 6.15 Insulation above the ceiling
Where to insulate
  • If the floor is a raised timber floor the
    sub-floor space should be enclosed, allowing for
    the required ventilation, and bulk insulation can
    be supported between the joists or reflective
    foil can be placed over the joists (see Figure

Figure 6.16 Insulation below the floor
Where to insulate
  • In extremely cold climates rigid foam insulation
    around the edges of the slab is advantageous (see
    Figure 6.17).

Figure 6.17 Insulation around the edges of the
Where to insulate
  • In timber walls bulk insulation can be placed
    between studs (see Figure 6.18).

Figure 6.18 Insulation between the studs
Where to insulate
  • Foam in-situ insulation can significantly
    increase the thermal performance of cavity brick
    walls (see Figure 6.19).

Figure 6.19 Insulation between walls
Where to insulate
  • The thermal performance of windows can be
    increased dramatically with double glazing or
    even triple glazing in extremely cold climates.
  • Full length drapes with pelmets will also greatly
    reduce heat loss.

Figure 6.20 Drapes and pelmets Check your
progress 3
Where to insulate
  • Although materials can be introduced to improve
    the thermal performance of the building, total
    energy efficiency requires attention to the
    design of the building as a whole. Some of the
    aspects which deserve attentionmainly those
    which can be easily attended tohave been touched
    upon in this unit.

  • You should now be able to list the types of wall
    and ceiling lining and insulation commonly used
    in Australia and be able to compare and contrast
    the properties associated with each and the
    applications they are suited to. Now go to Unit 7
    which covers metals and glass.

  • For hundreds of years people have been finishing
    the internal and external walls of their
    buildings with various mixtures or fabrics to
    decorate, preserve or waterproof them. Very early
    on, kalsomine (made from powdered limestone) was
    used to paint interior walls and varnishes and
    shellac were developed to preserve and decorate
  • Lacquers, made from resins, came from China
    originally and became very popular in late
    seventeenth and eighteenth century Europe for
    furniture and wall panels. In sixteenth century
    France painted hessian was popular as an interior
    wall finish, later superseded by exotic materials
    such as brocades. Wallpaper, as we know it, did
    not become really popular until the middle of the
    nineteenth century when printing processes made
    available brightly coloured and patterned
    wallpapers at prices many people could afford.
  • These days many coatings and coverings are now
    made either entirely or partially from plastics.

  • Today we expect a surface coating or covering to
    contribute to or provide any or all of the
  • decoration
  • preservation
  • waterproofing
  • hygiene
  • improved lighting
  • safety.
  • Surface finishes may only represent up to 5 per
    cent of the initial building cost but contribute
    greatly to the maintenance costs of the building.
    Selection of the correct system and adequate
    preparation of the surface is, therefore,

Learning outcomes
  • On completion of this unit, you should be able
  • distinguish between the alternatives available in
    the range of surface finishes
  • select a suitable finish, taking into account the
    background, location and durability requirements
  • describe suitable preparation and application

  • Composition
  • Broadly speaking, paint is a mixture of
  • the binder
  • pigments
  • additives and extenders
  • the medium.

  • The binder, as the name suggests, binds the other
    ingredients together, forming a solid, elastic
    film which must adhere to the surface, sometimes
    penetrating and sealing it as well. A paint is
    classified according to the type of binder.

  • Oil-based paints
  • These are based on oils which react with the
    oxygen in the atmosphere to solidify. Straight
    oil paints based on naturally drying oils, such
    as linseed oil, are rarely used today and have
    been largely supplanted by paints modified with
    synthetic binders called alkyds. These paints are
    often called enamels or alkyd enamels.
  • Water-based paints
  • These binders comprise small globules of resin
    which are suspended or dispersed as an emulsion
    in water. As the water evaporates, the globules
    coalesce to form a solid film. Paints based on
    this type of binder are commonly known as plastic
    or latex paints and the resins used include PVA,
    acrylic, polyurethane or combinations of these.
    They are often referred to as emulsion paints.
  • Solvent-based paints
  • These binders are dissolved in a solvent which
    evaporates leaving a solid film, such as lacquer
    and chlorinated rubber.
  • Chemically cured paints
  • These are usually two-pack paints and the binder
    forms as the two compounds are mixed together and
    react chemically. Once mixed, the paint must be
    applied within a few hours. Epoxy (epoxide) resin
    paints are examples.

  • Pigments are used to make the paint opaque, to
    hide the background, and to provide the required
    colour. For instance, titanium dioxide is used
    for opacity and another compound such as iron
    oxide might be used to impart the colour.

Additives and extenders
  • Additives and extenders are included in varying
    quantities and have a great influence on the
    properties of the paint. The roles of additives
    and extenders tend to merge but basically they
    are as follows.
  • Additives might include fungicides and driers in
    oil and alkyd paints or dispersing and
    emulsifying agents in latex or plastic paints.
  • Extenders are used to achieve the required
    viscosity, body and surface appearance.

  • The medium can either be a solvent in which the
    binder is dissolved or a dispersing medium in
    which it is suspended. Examples of solvents
    include mineral turpentine or benzine
    derivatives. The dispersing medium most commonly
    used for plastic and latex paints is water.
  • Thinning and cleaning up depends on the nature of
    the dispersing medium. Oil-based paints require
    turpentine or white spirit whereas water-based
    paints can be thinned and cleaned up with water.
    Special solvents are required for other types of

Paint systems
  • Most paint systems include the following
  • primer or sealer
  • undercoat(s)
  • finishing coat(s).
  • The choice of system depends on the nature of the
    surface to be painted and the finish required
    (see Figure 8.1).

Each component of the system performs a
particular function but in some cases, as with
plastic paints, a paint can perform more than one
function. The type of coat selected must be
compatible with the substrate (background) and
with adjacent coats.
  • The primer can fulfil a number of functions
  • providing a key to improve the adhesion of the
    next coat
  • sealing porous surfaces which would otherwise
    absorb part of the next coat and spoil the finish
  • minimising bleeding of surfaces such as bitumen
    and timber.
  • Primers which etch the surface and inhibit
    corrosion are available for use on metals.

  • Undercoats must cover the original colour of the
    surface and fill in any small depressions.

Finishing coats
  • Finishing coats provide the final colour and
    texture and offer the final protection against
    weather, chemical and mechanical damage.
    Finishing coats are available in gloss,
    semi-gloss or satin, flat or matt and in various
  • gloss is highly reflective, resistant to moisture
    and easy to clean but shows up surface
  • semi-gloss is less reflective and shows fewer
    surface imperfections
  • flat has low light-reflection, is usually
    permeable to moisture and tends to collect grime
    more easily.
  • Figure 8.2 demonstrates how, on a microscopic
    level, the medium evaporates leaving various
    amounts of pigment exposed, thus forming the
    various finishes.

Figure 8.2 Microscopic cross sections showing
how light is reflected, giving characteristic
shiny or matt appearance
Choosing a paint system
The nature of the substrate
  • The substrate is the surface which is to be
  • Alkalinity, porosity and loose particles on the
    surface to be painted can affect the adhesion and
    durability of a paint system.
  • Materials such as concrete, cement render, mortar
    and solid plaster contain small amounts of
    alkaline materials (mainly from the lime) and
    some paints, such as the alkyd enamels, are
    susceptible to alkali attack, which causes
    breakdown of the film. The gloss and semi-gloss
    enamels are more susceptible than the flat
    enamels and must be separated from the substrate
    by an alkali sealer.
  • Gloss and semi-gloss alkyd enamels are also
    adversely affected by porous surfaces which
    absorb the medium and binder unequally. The use
    of a suitable undercoat will prevent unequal
    absorption of the finishing coats. Plastic or
    latex paints are not affected by porous surfaces
    because the globules of resin are not absorbed
    but sit on the surface.
  • Loose surface material can reduce adhesion.
    Enamel paints tend to penetrate the loose
    material and bind it together but plastic or
    latex paints just tend to sit on the surface. For
    this reason, loose material should be removed
    with a brush or scraper before painting with a
    plastic or latex paint. If the surface is
    particularly loose, treatment with a 15 per cent
    solution of phosphoric acid may be required.

Recommended paint system
  • In addition to consideration of the nature of the
    substrate, the choice of a paint system
    ultimately depends upon
  • The performance specification
  • whether you require a fully impervious surface or
    a porous surface finish which can breathe
  • whether you require a high wear, abrasion
    resistant surface
  • whether the surface is to be washable
  • whether the surface is inside or exposed to
    weather and pollution.
  • Experimental Building Station Note on the Science
    of Building No 148 provides information on paint
    systems which is summarised in Table 8.1.

Special paints
  • A variety of paints for special purposes are
    available, including the following

water-resistant paints low-odour paints
chemical-resistant paints quick-drying paints
fire-retardant paints stoving paints
heat-resistant paints insecticidal paints
fungus-resistant paints permeable paints
anti-condensation paints floor paints
luminous paints multi-colour paints
fluorescent paints textured paints
phosphorescent paints metallic paints
radioactive paints
Applying the paint
  • On site, paint can be applied by
  • Brush which provides the best adhesion, desirable
    in priming coats, but skill is required to avoid
    brush marks.
  • Roller which is much quicker but provides a
    slightly stippled surface finish edges must be
    finished with a brush.
  • Spray equipment is expensive but can be
    economical on very large areas can be used to
    achieve metallic and graded effects the only
    suitable method for quick-drying paints the hot
    spray process reduces the viscosity of a paint
    without the addition of a solvent. In the
    factory, paint can be applied by
  • dipping smooththis is rapid and economical,
    producing a very smooth finish
  • flow coatingpaint is hosed onto the surface
  • roller coating (by machine)used for continuous

Preparation of surfaces
  • One of the most common causes of breakdown of
    painted surfaces is inadequate preparation of the
    substrate. Sometimes brushing is adequate but in
    other cases dirt must be removed by washing and
    scraping, using suitable solvents for oils and
  • Previously painted surfaces might simply require
    priming, filling and rubbing down but where a
    perfect surface is required paint can be removed
    by burning off and scraping, using solvent and
    chemical removers or by steam stripping.
    Water-soluble paints, such as tempera, must be
    removed before painting as they prevent the
    formation of a key.

When to paint
  • Generally speaking, it is best not to paint in
    wet, damp or foggy weather or below 4C, in
    direct sunlight or in dusty conditions. Humid
    conditions delay drying of ordinary paints.
  • Each coat should be thoroughly dry before the
    next is applied.
  • Good ventilation is required to assist drying and
    sometimes to remove noxious fumes.
  • Check progress 1

Clear finishes
  • Clear finishes are used to enhance the natural
    appearance of the substrate and in many cases
    waterproof and protect it as well. They may or
    may not include some colour pigment and,
    depending upon the type of compound, may be
    available in gloss, semi-gloss or matt finishes.
  • In general, clear finishes lack sufficient
    pigment to filter out damaging ultraviolet light
    and are therefore much less durable than paints
    in exposed conditions. Consequently, the choice
    is limited for external conditions.
  • Interior clear finishes have been formulated
    specially to suit the substrate. We will deal
    with them according to the nature of the

Clear finishes for internal timber
  • The clear finishes currently available include
    the following
  • Oil seal a type of varnish, used to achieve a
    water and grease resistant, non-slip finish for
  • Wax polishes based on natural waxes, such as
    beeswax, they can be used as complete system or
    to maintain other finishes. They are relatively
    soft and more inclined to collect dirt than other
    finishes they discolour when wet and will be
    stained by ink or heat but are less likely to
    show scratches and easily are repaired.
  • Polymer-based emulsions based on PVA, acrylic
    and polyethylene resins they are easy to apply
    and maintain.

Clear finishes for internal timber
  • The clear finishes currently available include
    the following
  • French polish based on applications of shellac
    and linseed oil in successive treatments,
    requiring great skill for a good finish. They are
    considered to be the most beautiful finish for
    internal timber but are extremely expensive and
    easily marked by water, heat and solvents.
  • Cellulose lacquer based on nitro-cellulose and
    a plasticiser and showing a similar appearance to
    French polish but less expensive and easier to
    apply. It is more resistant to water but
    eventually cracks and must be completely removed
    before renewing. Nitro-cellulose is extremely
    flammable and appropriate precautions should be
    taken regarding storage and use.

Clear finishes for internal timber
  • Short-oil varnishes have a low oil and high
    resin content, producing a high gloss but reduced
    flexibility. They are easy to apply with a brush
    but they dry slowly, collect dust and crack.
  • Spirit varnishes made with resins, such as
    shellac, they dry quickly by the evaporation of
    the solvent. They are cheap but brittle and
    inclined to crack.
  • Synthetic resin finishes made from plastics,
    such as phenol formaldehyde resins, urea
    formaldehydes, polyurethane and epoxides. They
    are available in one-pack or two-pack forms. They
    are relatively expensive but are very popular
    because of their ease of application by brush or
    spraying. They are rapid drying and are extremely
    hard and flexible, water and chemical resistant
    and heat resistant. Repairs are difficult because
    they cannot be removed by normal solvents.

Clear finishes for internal timber
  • When choosing a clear finish for a timber surface
    it is important to define your requirements
    carefully, taking into account the nature of the
    timber. For instance, the clear finish chosen may
    actually be harder than the timber substrate and
    breakdown of the finish has often occurred
    because an impact has caused denting of the
    timber below, not the finish itself. The result
    is a loss of bond between the substrate and the
    finish. Thus, softer timbers should be finished
    with the more flexible finishes.

Preparation of internal timber surfaces
  • As with painted surfaces, a good finish can only
    be obtained with adequate preparation of the
    substrate. In general, the surface must be clean,
    firm and dry but additional preparation might
  • bleaching or liming to give a grey effect
  • sanding to smooth the surface
  • stopping or filling of pores or indentations,
    usually with a tinted, oil-based wood filler
  • stainingthis may be applied before the final
    finish or may be included in the finish (the
    manufacturers advice should be followed
    regarding the compatibility of a stain with a

Clear finishes for external timber
  • Clear finishes which will help to preserve the
    natural appearance of timber in exposed
    conditions include the following
  • Preservatives These help protect the sapwood and
    heartwood or timber from attack by fungi and
    discolouration by moulds.
  • Water repellents These are a mixture of linseed
    oil, paraffin wax and a fungicide, applied by
    brushing or dipping, especially to end grain.
    They help preserve the appearance of the timber
    by reducing surface cracking due to wetting and
  • Stains Water-resistant stains can provide a
    degree of ultraviolet filtration change the
    colour of the timber and revive bleached timber.
  • Varnishes The only suitable varnishes for
    exterior use are long-oil marine and exterior
    varnishes but these require frequent
    recoatingless than four coats will be unlikely
    to last more than a year. While intact, varnishes
    seal the timber against water but it is desirable
    to apply a preservative as well.

Preparation of external timber
  • In general, a lower standard of preparation is
    required for external timber but any stopping or
    filling must be water-resistant and galvanised
    nails should be driven well below the surface and
    filled to avoid rust stains.

External clear finishes on other materials
  • Clear finishes designed to reduce soiling and
    make the surface impervious to water are
    frequently applied to masonry surfaces, finishes
    based on silicone being the most effective and
    the most expensive alternatives.
  • Finishes based on acrylic resins and polyurethane
    two-pack systems are available to give some
    protection to metals such as copper. They must be
    applied by spraying and preferably in a factory.

Other Coatings
  • Vitreous enamel (often called porcelain enamel)
    is actually glass which is fused under extreme
    heat to metal surfaces. The process is expensive
    but the resultant coating is extremely hard and
    durable and adheres firmly to the substrate so
    that where damage exposes the underlying surface,
    rust will not creep under the rest of the
  • The finish is applied after fabrication is
    complete and the number of coats required depends
    upon the location of the finished component.
  • A wide range of colours is available and finishes
    can be gloss, semi-gloss, matt or textured. The
    latter collect grime easily and are not suitable
    for external use.
  • Vitreous enamel coatings are used for metal-wall
    infill panels, mullions, lift panels, steel
    rainwater components and baths.

Plastics coating
  • Plastics can be applied in a number of ways to
    metal, timber and other surfaces and form
    continuous protective coatings which, in general,
    are more durable and tough than ordinary painted
  • Some are extremely durable (eg polyvinyl fluoride
    and nylon) but others (eg polyethylene)
    deteriorate in exterior conditions, fading and
    becoming brittle.
  • Many colours are available though some are not
    suitable for external use and the finish obtained
    is usually warm to the touch, and smooth, easily
    cleaned and provides electrical insulation.
  • The coatings are applied to the components or
    sheet materials in the factory and are used for
    sheet metal, and extruded components, such as
    handrails, in particular.
  • Check progress 2

Sheet coverings
  • As briefly mentioned at the beginning of the
    unit, sheet coverings such as wallpapers and
    fabrics have been used to decorate wall and
    ceiling surfaces for hundreds of years.
  • Wallpapers and textiles are still the easiest way
    to obtain large areas of highly patterned or
    textured wall surface and in addition can
    contribute to acoustic modification of the space.
  • Light-fastness varies and few are suitable in
    areas receiving strong sunlight.

Types of sheet coverings
  • Sheet coverings used frequently include the
  • Lining papers These are used to cover imperfect
    plaster surfaces which are subsequently painted
    or wallpapered. They are hung horizontally under
    wallpaper to minimise coincidence of joins.
  • Expanded polystyrene This is a great deal
    thicker than wallpaper and it provides some
    thermal insulation, often sufficient to prevent
    surface condensation.

Types of sheet coverings
  • Sheet coverings used frequently include the
  • Wallpapers These can be machine-made or
    hand-madethe latter being more expensive, with
    denser colours but some imperfections. Wallpapers
    are available in the following types
  • pulpspatterns printed directly onto the paper
  • embossedwith a raised design
  • duplextwo-ply papers
  • ingrainhaving fibres incorporated into the
  • washablecoated with a plastic emulsion,
    vinyl-faced papers are washable but maximum dirt
    resistance is provided by PVC coated papers
  • shinysurfaced with mica
  • flockraised applied patterns created by blowing
    fibres onto patterns printed in adhesive.

Types of sheet coverings
  • Wood veneer This can be mounted on paper, cloth
    or metal foil backings and is often coated with
    transparent vinyl.
  • Textiles A wide variety of textiles is
    available, such as hessian, silk and synthetic
    fibres, which can be used unbacked in folds or
    stretched taut on frames or backed with paper,
    foamed plastic or PVA.
  • Leather Usually backed with padding such as
    foamed plastic, panel sizes must be limited to
    available hide sizes.
  • Plastic-faced cloths PVC-impregnated cotton
    cloths are produced in a wide range of colours,
    textures and patterns. They are waterproof and
    can be cleaned with warm water and soap or mild,
    domestic non-abrasive chemicals.
  • Grass cloth This consists of bamboos or grasses
    held together with thread and mounted on
  • Carpet Stapled to vertical surfaces, carpets can
    provide a durable, soft finish with excellent
    sound modification characteristics.

Hanging wallpapers and other sheet coverings
  • There are some important considerations when
    hanging wallpaper
  • It is best if patterns are matched at eye level
    to minim
  • ise obvious irregularities in printing or stretch
    in the paper.
  • Drying time is important for a good result and
    paper should be neither too wet nor too dry.
  • Care should be taken to avoid paste staining of
    the paper, especially flock papers.
  • Most ordinary wallpapers come pre-pasted with
    flour, starch or cellulose pastes which have good
    slip properties for hanging.
  • Heavy papers can be hung with special proprietary
    brand pastes.
  • Expanded polystyrene must be fixed with a PVA
    adhesive as other adhesives destroy it. If it is
    to be used as a lining paper it should be painted
    with plastic paints only.
  • Plastic-faced cloths must be fixed with adhesives
    recommended by the manufacturer.

Preparing the surface to be papered
  • The wall surface should be dry and chemically
    neutral with a slight suction. This is achieved
    by removal of efflorescence by brushing and
    painting with an alkali-resistant primer. If
    mouldy, old wallpaper should be removed and the
    surface treated with a fungicide. Depressions and
    cracks should be filled and a lining paper could
    be applied to improve the substrate.
  • Check progress3

  • Galvanising is the process of coating steel and
    iron with zinc to form a protective coating. The
    steel is lowered into a molten bath of zinc
    heated to approximately 500C and emerges with a
    shiny coating of zinc. The zinc coating acts as a
    sacrificial anode and corrodes to protect the
    steel. Since its rate of corrosion is slow, the
    steel can remain protected for hundreds of years,
    depending on the environment.

  • Zincalume is a newer protective coating and is a
    combination of zinc and aluminium (45 and 55
    respectively), which is applied in a factory
    process to sheet steel used for roofing and
    cladding in the building industry.

  • Surface finishes include paint, clear finishes,
    plastic coating, various types of wallpaper and
    other sheet coverings.
  • On steel and iron, galvanising is another method
    of coating the surface to protect it from
    deterioration. Surface finishes may be used to
    protect, preserve or waterproof interior and
    exterior walls, floors, ceilings and roofs. They
    are also used for decorative purposes and to
    improve the lighting in rooms.
  • If you have completed all the check your progress
    questions you are now ready to begin the final
    unit of this module, on plastics and adhesives.

Development of plastic products
  • In the twentieth century plastics have been
    developed to such an extent that they replace
    many natural materials. The term plastics is
    now used to describe many products which are
    artificially made and chemically produced.
  • Glues and adhesives have been made since ancient
    times and many of the materials were naturally
    occurring for example, bitumen and tree resins.
    The growth of the plastics industry has resulted
    in the discovery of many new adhesives from
    synthetic resins.

Learning outcomes
  • On completion of this unit, you should be able
  • differentiate between thermoplastic and
    thermosetting plastics
  • demonstrate a knowledge of the practical uses of
    plastics and adhesives in the building industry
  • describe the different adhesives in general use.

  • The term plastics as it is commonly used today,
    refers to a large group of synthetic materials
    which may be derived from coal, natural gas or
    other petroleum products, cotton, wood and waste
    organic products such as oat hulls, corn cobs and
    sugar cane. From these substances, relatively
    simple chemicals, known as monomers, are
    produced. Monomers are capable of reacting with
    each other and are built up into chain-like
    molecules called polymers.
  • Rubber products, which are derived from a
    naturally occurring organic base, have in some
    cases been superseded by plastic products which
    can have similar or superior properties.

Development of plastic products
  • Plastics have had a profound effect on nearly
    every facet of our society and the proliferation
    of plastic products has meant that practically
    everyone is in almost daily contact with plastics
    in one form or other. In the building industry,
    like everywhere else, plastic products have taken
    over from many traditional materials.

Types of plastics
  • Plastic materials fall into two groups
  • thermoplastics
  • thermosetting plastics.
  • Thermoplastics
  • These become soft when heated and harden again on
    cooling, regardless of the number of times the
    process is repeated. However, there are practical
    limits to the number of times that thermoplastics
    can be heated and cooled too many times affects
    the appearance and strength of the product.
  • Thermosetting plastics (thermosets)
  • These undergo an irreversible chemical change
    during production, in which the molecular chains
    cross-link so that they cannot subsequently be
    appreciably softened by heat, while excessive
    heating will cause charring.

General properties of plastics
  • Plastics vary considerably in behaviour and
    specific differences will be discussed under
    individual plastics. Some properties common to
    most plastics are
  • strength
  • thermal conductivity
  • electrical insulation
  • combustibility
  • durability
  • non-biodegradability.

  • Most plastics have tensile strength-to-weight
    ratios which are higher than many metals but
    their greater elasticity precludes plastics from
    most structural applications. Also, plastics tend
    to creep and degrade at elevated temperatures,
    resulting in reduced strength. Thermal expansion
    can be as much as ten times that of steel.
  • Thermal conductivity
  • Expanded plastic materials have relatively low
    thermal conductivityhence the suitability of
    foamed plastics, which contain air bubbles, as
    insulation material.

  • Electrical properties
  • Plastics do not conduct electricity and are
    therefore excellent insulators but electrostatic
    charges can build up on plastic surfaces and
    attract dust, and sparking could be hazardous in
    some situations.
  • Combustibility
  • Many plastics are combustible and the spread of
    flame over some plastic surfaces is high. When
    burning, plastics produce a great deal of smoke
    and it is the noxious gases emitted and the
    tendency of some plastics to melt rapidly which
    present the major safety hazards.

  • Although plastics do not rot or corrode, in many
    cases they have not been around long enough for
    their durability to be adequately assessed.
    Ultraviolet radiation from the sun is responsible
    for breakdown and colour change in some plastics,
    especially in the presence of heat. Some pigments
    behave better than others in exposed conditions
    and advice from manufacturers should be sought
    regarding suitable colours for outdoors. Some
    plastics, acrylics and PVC, in particular, have
    performed well outside for a number of years.

Environmental hazards
  • Plastics are not biodegradable and the disposal
    of plastic products is of environmental concern.
    In the past, and to some extent at present,
    plastics were disposed of by burning which causes
    serious atmospheric pollution. Plastics have also
    been disposed of by burial which causes problems
    because they do not break down for many years.
    Today many plastics are recycled.

Properties and uses of specific plastics in
  • Plastics can be formed by a variety of processes
    according to the type of plastic and the end
    product required. The applications of plastic
    products in buildings are numerous, as are the
    number of plastics available. Although the list
    below might seem endless, only the most
    frequently used plastics are described and since
    plastics are being used so widely you should be
    familiar with the properties of at least the most
    common varieties.

  • Polyethylene (polythene)
  • This is available in low density and high density
    forms. It has a high degree of impermeability to
    water and water vapour. Its toughness and
    chemical resistance make it suitable for
    waterproof membranes, for cold water cisterns,
    for bath, basin and sink wastes and cold water
    pipes. Its high thermal movement, however, makes
    it unsuitable for hot water pipes.
  • Polyethylene is suitable for waterproof
    membranes, for cold water cisterns, for bath,
    basin and sink waste pipes and cold water pipes.
    It is unsuitable for hot water pipes.
  • Polyvinyl chloride (PVC)
  • PVC is produced in several forms. In its rigid or
    unplasticised form (UPVC) it is used for soil and
    rainwater pipes and for electrical conduits and
    accessories. In transparent, translucent and
    opaque sheets it is used for roofing or wall
    cladding. The plasticised or flexible form is
    used in vinyl floor coverings, electrical cable
    insulation and sarking.
  • PVC burns only with great difficulty and is
    self-extinguishing, which makes it suitable for
    air-conditioning ducts.

  • Polyvinyl acetate (PVA)
  • Because of its low softening point, PVA is
    limited to use in adhesive for joinery, emulsion
    paints, bonding agents for plaster, cement
    screeds and in situ floor coverings.
  • Polymethyl methacrylate (acrylic)
  • Because of its high transparency in the clear
    form (92 per cent compared with 90 per cent for
    glass) and high resistance to impact (greater
    than glass), acrylic is used extensively for
    corrugated sheeting, roof lights and light
    fittings. However, large areas of acrylic burn
    rapidly and the melting plastic drops from roofs.
    It should, therefore be avoided for large areas
    of roofing.

  • In its unmodified form, polystyrene tends to be
    brittle, easily attacked by certain organic
    solvents and readily burnt. It is low in cost and
    is used for cisterns, light fittings and concrete
    formwork and in some paints. Expanded or foamed
    polystyrene is used for building boards, and both
    rigid and loose-fill insulation.

  • Polytetrafluoroethylene (teflon)
  • Teflon is highly resistant to heat and has very
    low friction characteristics however, it is
    extremely expensive and is used only for special
    applications such as PTFE (plumbers) tape which
    is used to give a tight friction fit mainly
    between threaded brass connections.
  • Polyamide resins (nylons)
  • There are many forms of nylon. They are tough,
    very strong and hard wearing and have low
    friction characteristics. Unlike other plastics,
    they absorb up to 2 per cent of water, swell
    slightly and burn only with difficulty. Apart
    from use as a fibre in carpets and upholstery
    materials, nylons are used for nuts and bolts,
    castors, curtain rails and sliding door fittings
    and ball valve assemblies.
  • Polycarbonates
  • Extremely high in cost, but with remarkable
    properties, polycarbonates are dense and hard
    with a high ductility and tensile strength like
    metals. They are transparent (86 per cent light
    transmission), with a high softening point, and
    are virtually self-extinguishing. They are used
    for roof glazing and vandal-proof and bulletproof

  • Phenol formaldehyde (bakelite)
  • One of the oldest of the plastics, first produced
    commercially in 1910, bakelite is also the
    cheapest thermosetting plastic. It is usually
    dark in colour and because it is a good insulator
    and resistant to ignition, its uses include
    electrical and door furniture mouldings, and in
    adhesives, paints and foamed applications.
  • Urea formaldehyde
  • Urea formaldehyde products are usually white or
    brightly coloured and it is self-extinguishing.
    It is used for electrical accessories, paints,
    stoving enamels, adhesives and foamed products.
  • Melamine formaldehyde
  • Melamine formaldehyde can be made in a wide
    variety of bright, permanent colours it is
    resistant to hot and cold water and cigarette
    burns. Its major use is as a surface to paper
    laminates such as laminex or formica, which
    creates a durable sheeting material suitable for
    high-wear horizontal or vertical surfaces such as
    kitchen benchtops and waterproof cupboard and
    wall linings. It is also used for mouldings and
    in adhesives.

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