The most common materials to be painted on house exteriors are weatherboards and fibre cement sheets. The paint chosen should be one that has good durability. Most well-known label paints will give good life; remember that white is the preferred colour as it resists ultraviolet attack better and resists fading. Acrylics seem to perform extremely well.
There are some high-strength exterior paints that contain materials such as synthetic resins, asbestos, perlite, zinc oxide, siliceous aggregates and titanium oxide. They are sometimes used to provide long-life coatings; recoating is difficult and needs to be done by specialist contractors. It is worth checking the asbestos content in some of these products.
Painting Timber Weatherboards
Timber weatherboards must have all flaking paint removed by hot air and scraping. Any remaining paint must be well sanded to remove any cratering and to provide a key for new paint.
Raw patches of timber must be spot primed with pink primer to preserve the wood; the whole area can then be painted with either two coats of acrylic paint, or an oil-based undercoat and two top coats.
Painting Doors
Doors, both inside and out, must be well painted to stop delamination of the ply. They should be coated all round, including bottom and top. This can only be done prior to installation.
Doors should be coated with enamel paints, as these are more resistant to the constant wear and tear. The paint system is the normal one for oil-based paints.
The doors should be first washed down with sugar soap and water, and then sanded thoroughly to key the existing gloss paint. Once this has been done, apply an undercoat, followed by two or more final coats, depending on colour cover. Brushing is the most successful technique.
Repainting Windows
Windows have the extra problem of being difficult to prepare because of the many angles, nooks and crannies. If there is flaking paint, it should be cleaned up with a hot-air gun and a shaving hook to remove all loose paint. The remainder can be sanded to provide a key to the new coats, and to smooth any cratering.
Any raw timber must be treated, preferably with a wood preservative and then with a pink primer, as a preparation for the application of an oil-based undercoat and two top coats. Also, paint the putty to seal it against drying out and cracking. The paint film extends to about 1mm onto the glass to provide a complete seal.
Repainting Cement Surfaces
Cement rendering is the wall finish used in many homes and units. Some exteriors are rendered and then painted for waterproofing.
The problem with this is that every two years the paint seems to flake on the exterior. Some special preparation is recommended. This is due to the reaction of an alkaline substance, such as render, with oil-based materials.
Cement render is slightly alkaline and if oil-based coatings are painted on direct, you may end up with something like soap. The best coating to use is an acrylic.
Oil paints may still be desirable to use because of their abrasion resistance. If this is so, the undercoating system will need to include an alkali sealer, before being coated with normal undercoat and oil-based finish.
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