HOW TO PAINT A TILED ROOF
HOW TO PAINT A TILED ROOF
What are roof tiles?
Roof tiles are usually made from cement or from clay (less common).
Cement tiles are prone to carbonation due to the effects of carbon dioxide and water in the atmosphere that form a very weak acid called carbonic acid, which extracts the cement from the surface of the tiles and produces a weak, friable surface layer. As cement roof tiles age this becomes more severe.
While clay tiles do not have this problem, they do tend to be highly porous, resulting in poor paint film curing.
Surface preparation is the critical part of any painting project, with poor preparation being the principal cause of coating failure. The object of surface preparation is to provide a strong surface bond before applying any paint. Both tile types can be prepared as follows:
1. Wash the surface thoroughly using water and a strong brush. This should remove all loosely bound sand particles and any poorly adhering paint coatings. Use of a high-pressure water jet is recommended.
2. Rinse the roof with clean water and then leave it to dry out. The moisture content, which can be measured using a moisture meter, should be below 15%.
3. Check the adhesion of any existing paint coatings by pressing adhesive tape (e.g. masking tape) onto the dry surface. Pull the tape off the surface and inspect the underside of the tape.
• If no coating has come off, and there is no dirt or chalky material visible on the tape then the surface is suitable for painting. *
• If the surface is chalky or a powdery layer is visible on the tape apply a quality Bonding Liquid.
• If sandy particles are removed the surface is friable and the surface must be rewashed.**
• If the paint coating comes off, the surface under the coating is weak and should be stripped, and the cleaning process repeated.
* Check the porosity of the surface before painting by applying a droplet of water. If it is easily absorbed into the tile then the application of a quality Bonding Liquid, to seal any residual particles, is recommended.
** As it may not be possible to remove all sand particles the application of a quality Bonding Liquid, to seal any residual particles, is recommended.
4. If a quality Bonding Liquid has been applied to the surface, it must be left to harden for at least two to four hours before continuing.
Apply Promac Roofcote to the prepared surface using a roller (wool or synthetic type), brush or by airless spraying. For optimum durability and a quality finish that application of two coats is recommended. Allow the first coat to cure for at least two to four hours before applying the final coat.
Calculating the required amount of paint
1. Estimate the plan area of the roof by measuring the length and breadth of the walls.
2. Multiply this area by 1,5.
3. Estimate the paint quantity needed by dividing the above area by 7, multiplied by 2 for two coats. This should result in a slight excess of paint, which is useful for touch-up work when required.
Other important information
1. Never apply paint if rain is forecast, or expected, during the day of application.
2. Apply paint after 08h00 (summer) or 10h00 (winter) to ensure that the roof is not too cold or damp.
3. To avoid excessive roof temperatures and to allow the paint to harden sufficiently before any afternoon rain may occur, painting before 12h00 is recommended.
4. To reduce colour variations always use the same batch number for touch-up work, which may otherwise be visible on the painted roof.
Description of paint / products mentioned above
1. Promac Bonding Liquid Water-Based Nano-Tech is an alkali-resistant, deep-penetrating bonding sealer for a wide range of friable surfaces such as gypsum and cement plasters. It increases substrate strength for optimum durability of all finishing coats.
2. Promac Roofcote acrylic is a high-quality, acrylic, medium-sheen finish paint with outstanding weathering and alkali-resistant properties. It can be applied on to suitably prepared fibre-cement tiles, roof sheet, clay or cement roof tiles and pre-primed galvanised iron roofs. It is available in the
following colours: black, grey, burgundy, red, brown, terracotta and green.