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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 differently—according 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 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.
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.
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).
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 lime—refer 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 Keene’s 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.
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.
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. Keene’s 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.
Table 6.1: Mixes for undercoats for internal two-coat and three-coat work
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.
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.
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).
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.
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
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 carports—4.5 mm or 6 mm sheet; for internal wall and ceiling linings—6 mm; compressed fibrous cement for wet area floors is 15 mm or 18 mm thick.
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.
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.
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.
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
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.
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.
Heat transfer • Heat is transferred by: • conduction—heat is ‘led’ from the side of the material at a higher temperature to the side at a lower temperature • convection—when air is heated it expands and begins to circulate and heat up colder surfaces by losing some of its heat to them • radiation—when air comes in contact with a warm object, heat is transferred to the atmosphere.
Thermal resistance • A material’s 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.
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.
Bulk Insulation • This is normally a cellular material with entrapped air bubbles which slow down heat transfer by conduction. Several forms are available.
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 1000°C 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.
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 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.
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 panels—decorative 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.
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 manufacturer’s 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.
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 6:16). 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 slab
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 attention—mainly those which can be easily attended to—have been touched upon in this unit.
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.
