Fibre/Asbestos cement occurs in several forms in buildings, mainly as wall partitions, ceilings, roofing sheets (plain, corrugated), tiles, gutters and down pipes. This material is very absorbent, often highly alkaline, and may contain relatively high concentrations of salts.
“Oil” paints may not be used on new exterior fibre cement surfaces. Blistering and peeling may be caused by moisture which may persist due to entry from the back of the surface, e.g. when gutter, downpipes, etc., are not internally painted and the continued flow of rainwater maintains damp conditions within the asbestos cement.
Fibre/Asbestos cement should be dry before painting. Gutters, (bituminous solution is recommended for inside of gutters), window sills, fascia boards, etc., should be painted on both sides to prevent moisture penetration. For external asbestos cement surfaces, 100% acrylic type emulsion paints or Dekrolite Masonry Paint are preferred because of their high alkali resistance.
Fungus tends to grow on unpainted asbestos cement because it is alkaline and porous, holding moisture and food for spores. It is therefore highly recommended to waterproof unpainted surfaces with Aquablock Water Repellent.
Ensure surfaces are clean and dust free.
Previously limewashed or distempered:
Remove to bare substrate.
Previously oil, alkyd, P.V.A. or acrylic painted:
If existing paint is in poor condition, remove by scraping or with Dekro Super Paint Stripper. Wash down with a suitable concentrated detergent solution, rinse and allow to dry. If the existing paint is in good condition wash with soap and water, a suitable concentrated detergent or solvent to remove dirt, grease, wax polish or other contaminants. Abrade glossy surfaces to form a key for subsequent coats, rinse clean – allow to dry.
Previously painted or unpainted covered with fungus:
Remove visible fungi and dirt with a suitable asbestos cleaner. Sterilise surface by applying an HTH solution or one coat Hydrowash Fungicidal and leave overnight to dry. Brush down with a stiff bristle brush. Rinse with clean water and allow to dry.