Wall

1
Wall Ceiling Linings
2
Introduction

• 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.

3
Learning outcomes

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

4
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
  plaster.
• 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.

5
Plaster

• 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
  example).

6
Composition

• 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
  used.
• 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.

7
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.

8
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.

9
Limes

• Plasters in which limes are the only binders are
  rarely used today as the final strength is very
  low.
• 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.

10
Process

• 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
  coats.
• 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
  plasterwork.

11

• 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)
12

• Table 6.2 Mixes for finishing coats for internal
  work

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
13
Preparation

• 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
  preparation.

14
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
  conditions.

15
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
  material.
• 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).

16
Figure 6.1 Fixing
17
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
  building.
• 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.

18
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
  plaster.
• 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

19

• 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
  thick.

20
Fixing

• 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.

21
Uses

• 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.

22
General Properties

• Thermal insulation Fibrous cement sheets are
  relatively thin and make a correspondingly small
  contribution to the thermal insulation of the
  building.
• 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.

23
General Properties

• Sound insulation The sheets have a greater
  density than plasterboard but are thinner and
  therefore do not significantly affect sound
  insulation.
• 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

24
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
  6.7)
• 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.

25
Figure 6.4 Paths of the sun in winter and summer
26
Figure 6.5 Location in relation to summer breezes
27
Figure 6.6 Protection from winter winds
28
Figure 6.8 The use of wide eaves or pergolas
29
Figure 6.10 Interior planning
30
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
  ceilings.

31
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.

32
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
  area.

33
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
  available
• 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
  conduction.
• 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.

34
Bulk Insulation

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

35
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
  sheets.
• Urethane foam sheet, made from foamed
  polyurethane.
• Expanded polystyrene sheet (EPS), made from
  foamed polystyrene.

36
Loose fill

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

37
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
  area.
• Urethane foam is pumped as fluid foam into the
  space where it sets chemically to form a rigid
  insulation.
• Expanded polystyrene beads are mixed on site with
  a bonding agent and injected into the cavity.

38
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
  finishes.
• 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
  together.
• Expanded polystyrene, as above with decorative
  finishes.

39
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
  Methods.
• 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.

40
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.

41
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
42
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
43
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
  616).

Figure 6.16 Insulation below the floor
44
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
slab
45
Where to insulate

• In timber walls bulk insulation can be placed
  between studs (see Figure 6.18).

Figure 6.18 Insulation between the studs
46
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
47
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
48
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.

49
Summary

• 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.

50
Paints
51
Introduction

• 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
  timber.
• 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.

52
Introduction

• Today we expect a surface coating or covering to
  contribute to or provide any or all of the
  following
• 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,
  important.

53
Learning outcomes

• On completion of this unit, you should be able
  to
• 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
  techniques.

54
Paints

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

55
Binder

• 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.

56
Paints

• 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.

57
Pigments

• 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.

58
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.

59
Medium

• 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
  paints.

60
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).

61
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.
62
Primer

• The primer can fulfil a number of functions
  including
• 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.

63
Undercoats

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

64
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
  textures.
• gloss is highly reflective, resistant to moisture
  and easy to clean but shows up surface
  irregularities
• 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.

65
Figure 8.2 Microscopic cross sections showing
how light is reflected, giving characteristic
shiny or matt appearance
66
Choosing a paint system
67
The nature of the substrate

• The substrate is the surface which is to be
  painted.
• 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.

68
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.

69
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
70
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
  lengths.

71
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
  stains.
• 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.

72
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

73
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
  substrate.

74
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
  floors.
• 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.

75
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.

76
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.

77
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.

78
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
  include
• 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
  finish).

79
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
  drying
• 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.

80
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.

81
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.

82
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
  coating.
• 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.

83
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
  finishes.
• 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

84
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.

85
Types of sheet coverings

• Sheet coverings used frequently include the
  following
• 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.

86
Types of sheet coverings

• Sheet coverings used frequently include the
  following
• 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
  surface
• 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.

87
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
  backings.
• Carpet Stapled to vertical surfaces, carpets can
  provide a durable, soft finish with excellent
  sound modification characteristics.

88
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.

89
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

90
Galvanising

• 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.

91
Zincalume

• 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.

92
Summary

• 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.

93
Development of plastic products
94
Introduction

• 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.

95
Learning outcomes

• On completion of this unit, you should be able
  to
• 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.

96
Plastics

• 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.

97
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.

98
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.

99
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.

100
Strength

• 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.

101

• 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.

102
Durability

• 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.

103
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.

104
Properties and uses of specific plastics in
building

• 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.

105
Thermoplastics

• 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.

106
Thermoplastics

• 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.

107
Polystyrene

• 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.

108
Polystyrene

• 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
  glazing.

109
Thermosets

• 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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