The finished surface of a plasterboard wall or ceiling presents to the painter a surface which is composed of two different materials of differing texture and porosity. For a satisfactory finish - one in which these variations are not telegraphed through the paint film - the differences in surface characteristics must be addressed.

The manufacturers recommendation for the proper finishing of plasterboard is for the use of a suitable plasterboard sealer over the entire surface in order to equalise porosity.

Choice of colours is important as darker topcoat colours tend to highlight imperfections. White, or light colours, give better reflection and are particularly recommended for ceilings.

Painting Plasterboard

If gloss paints are to be used in large open plan rooms with large areas of uncurtained windows, then the highest level of finish is essential. However, if cost factors preclude this investment, then very careful consideration must be given to:

• The placement of windows
• The type of lighting
• The standard of paint finish
• The positioning of both butt and recess joints

Paint Systems

Various systems of paint finish are available in varying qualities. The principle "you get what you pay for" applies in this as in many areas.

• Two coat paint systems - either two coats of finishing paint or one coat sealer and one top coat are common in the industry. Two coat systems are not recommended as they will almost invariably fail to obscure the joints and variations in porosity and texture.

• Three coat paint systems - typically one coat sealer followed by two top coats is the minimum specification recommended.

  Preparation & Application

  The following comments should be taken as a guide for the preparation and paintings of plasterboard.

  1. All surfaces should be clean and dusted down prior to painting.

  2. First coat should be a recommended plasterboard sealer rolled or sprayed - lightly sand when dry.

  3. Apply two top coats (undiluted) - paint with brush, roller or spray (back rolled).

  4. It has been a long-standing recommendation of plasterboard manufacturers, that roller application of paints is preferred as the light dimpling imparted by the roller gives greatest obscuration of surface characteristics.

  Gloss Paints

  Gloss paints and even semi-gloss paint on flat surfaces reflect light in a pattern distorted by the imperfections of the surface. This effect is enhanced as the observer moves around the room. Flat paints on the other hand tend to reflect light back in a diffused form which does not draw the attention of the observer to surface undulations or imperfections.

  It should be pointed out that plasterboard is a machine made product with a textured paper surface and that the jointing is a hand applied operation. When sanded the two different surfaces are evident and for this reason - gloss paints should be avoided where possible.

  It should be emphasised that in some cases gloss paints may be desirable for purely functional reasons, e.g. kitchens, bathrooms, etc. In which case some loss of appearance will have to be accepted. Even when the work has been carried out by the most highly skilled tradesmen, the end result can be most disappointing when gloss paints are used for decorating purposes.

  Spraying Paint

  Contrary to popular belief, the spray method of painting has not been recommended for the painting of plasterboard and has gained a bad reputation through over-dilution of paint, poor tradesmanship and reluctance to back roll the freshly applied surface.

  The spray method of painting aggravates face paper napping and highlights joint lines. Spray application does not assist in equalising the surface of what is basically two completely different materials. (Paper faced plasterboard and porous joint compound).

  It is a fact that a good plastering job can be made to look quite ordinary by poor painting practices.

  If spray painting is to be used, the following steps are recommended:

  1. Prepare as for other applications.
  2. Apply seal coat and wipe over joint lines and adjacent board with fine sandpaper when dry.
  3. Spray first top coat and back roll with a dry roller immediately behind the spray gun.
  4. Spray final coat and back roll if required - i.e. if joints are still visible.
  5. Use premium quality paints only.
  6. Do not dilute beyond manufacturers recommendations.