Poor Alkali Resistance

Colour loss and overall deterioration of paint film on fresh masonry.

Possible Cause

• Coating was applied to new masonry that has not cured for a full year. Fresh masonry is likely to contain lime, which is very alkaline. Until the lime has a chance to react with carbon dioxide from the air, the alkalinity if the masonry remains so high that it can attack the integrity of the paint film.

Solution

Allow masonry surfaces to cure for at least 30 days, and ideally for a full year, before painting. If this is not possible, apply a quality, alkali-resistant sealer or water-based primer, followed by a top-quality 100 percent acrylic exterior paint. The acrylic binder in these paints resists alkali attack.

Images courtesy of the Paint Quality Institute from Dow Coating Materials