Building boards

The term building board is a very general term which covers a wide variety of materials. Building boards can be made of wood, compressed sawdust or vegetable fibre gypsum plaster etc.

Many building boards are supplied pre-primed or factory finished. Some are treated with fire resistant chemicals, in which case it is important to seek the board manufacturer's advice before painting.

Most building boards will be hidden from view, in that they will be plastered over, used as flooring or as an insulation material, in which case the board itself will not be painted.

Some of the building boards listed here may no longer be manufactured, but they are worth mentioning due to the odd occasion when they may be encountered, particularly in older buildings.

Where building boards have previously been painted, the actual substrate becomes less important as you are specifying paint for an existing coating (e.g. Gloss or Emulsion) not the board itself, therefore it is the compatibility of the paint coatings that becomes the important issue. Surfaces that have previously been painted with conventional decorative solvent-based paints such as gloss or eggshell should not be repainted with normal emulsion paints, particularly in areas subject to frequent or heavy condensation. The exceptions to this rule are the quick drying water-based gloss and eggshell paints, as they are formulated using a unique adhesion promoted latex which enables them to adhere well to this type of surface.

Emulsion paint may be overcoated with a conventional decorative solvent-based system such as gloss or eggshell if it is considered necessary for improved durability. When specifying solvent-based paints for use on large surface areas inside, or in small confined spaces inside, the wearing of air supplied breathing equipment by the decorator will normally be necessary, in order to comply with a COSHH Assessment as required under the Control Of Substances Hazardous To Health Regulations 2002.

Asbestos although not used any more, asbestos may be encountered when refurbishing older industrial units etc. It is a hazardous material and must be used in accordance with the recommendations of the Health and Safety Executive. The fibres of asbestos are a known carcinogen, so the nominated builder/decorator must refer to an appropriate COSHH Assessment before handling, preparing or painting this type of surface. The surface of Asbestos is highly alkaline and also permeable to moisture vapour. If a conventional decorative solvent-based paint such as gloss or eggshell is required then a priming coat of Dulux Trade Alkali Resisting Primer must be applied first to reduce the risk of saponification. It will be necessary to seal the back of the asbestos as well (if possible) to help prevent moisture permeating through to the back of the paint film, causing it to blister. Where this is not possible, a water-based emulsion paint will give better performance due to its higher rate of permeability. Emulsion paints also have the advantage of not being affected by alkali in the same way as solvent-based paints and so can be applied direct to the surface.

Calcium silicate boards have now replaced asbestos as a general purpose building board since they are much safer to use. They are similar in appearance to asbestos boards but do not contain any asbestos fibre and so do not present the same health risks. Calcium Silicate boards come in a variety of types and finishes, some have a wood grain effect and are used for cladding purposes. Like asbestos these boards are permeable to moisture vapour, so it is wise to use a water-based paint system, particularly when used for soffits and cladding etc. It is also advisable to specify painting the back of the boards before installation, especially if a conventional decorative solvent-based paint system such as gloss is required.

Cement based boards are a composition board made from cement, with various fillers such as glass fibres asbestos etc. They are similar in nature to asbestos boards. Cement based boards can be used externally and are normally only painted for cosmetic purposes.

Composite board is a general term that covers many types of blockboard, hardboard, laminboard, plywood and even plasterboard. It comprises of an outer skin glued to an insulating material such as cork, mineral fibre board or polystyrene. Some types have an aluminium foil backing as a vapour check.

Because there are so many different types on the market now, it is wise to check with the board manufacturer before painting a new or unknown type of board.

Composition ceiling tiles and acoustic tiles are used for suspended ceilings and normally have a self-finished surface. They are usually textured or perforated to give good acoustic properties and should not be painted, unless the degree of soiling is such that the surface cannot be cleaned successfully. Before painting this type of board, the manufacturers recommendations should be sought. If painting is carried out, careful application is needed to prevent the blocking of the perforations. Any paint coating will affect the acoustic quality of the surface. Matt emulsion paints usually provide the most satisfactory appearance.

Compressed straw slabs/strawboard are made from compressed straw which is faced with strong paper. They are normally treated with fire retardant materials to make the board fire resistant. The normal use for this type of board or slabs is for insulating walls or roofs and also for partition walls.

Expanded polystyrene is available as tiles or in sheet form. It has excellent insulation properties, but is very fragile and so easily damaged by impact or abrasion as well as being flammable, although fire retardant grades are available. Expanded polystyrene is for interior use only and must not be painted with solvent-based paints, as this will increase the fire hazard of this material and the solvents may even dissolve the polystyrene.

Gypsum plasterboard is made by sandwiching a layer of gypsum plaster between two sheets of heavy gauge paper. Plasterboard is normally used for dry lining interior ceilings and walls. Plasterboard has an ivory-coloured surface for direct decoration and a grey surface for plastering. There is a range of plasterboard available that has a moulded decorative finish which is ideal for use in mock panelling work.

Wood cement particle board is a particle board that is bonded with cement. It is much more fire resistant than the normal types of resin bonded chipboard. Because the surface is bonded with cement it is highly alkaline.