Paint Problem: Paint Peeling Off Brick

Paint Problem:  Painting Peeling From Brick

The most common cause of peeling from surfaces composed of mortar, brick, building block or concrete is efflorescence. Soluble salts are contained in these materials. When dissolved by water, they will be carried to the surface and will remain there after the water has evaporated. These crystallized salts push the paint away from the surface and peeling results.

Sometimes efflorescence occurs on brick walls of new construction. In the past, it was a common building practice to wash new brick or concrete walls with muriatic acid to clean away excess mortar. The acid was then washed away along with any chloride salts which may have formed. However, if the final rinsing was not thorough and the wall was painted later, any salts left on the bricks absorbed the moisture swell, causing peeling. (Current thinking is that acid etching, especially with muriatic acid, actually adds chloride salts back into concrete, so it is best to avoid it.)

Not all peeling from masonry is caused by efflorescence. Peeling can occur when an alkyd or oil-based paint is applied over a surface with a high alkalinity content (for example, unetched concrete). Alkyd resins that come in contact with an alkaline surface react by forming a soap film between the concrete surface and the alkyd coating. This reaction (saponification) results in extremely poor adhesion by the alkyd coating.

Solution

If efflorescence is evident, it must be removed before repainting. First, remove all flaking or chalking paint from the damaged area by wire brushing, sandblasting, or high-pressure water washing.Fill all cracks with a masonry patching compound, latex concrete patch, or caulking compound. If the surface is very porous, apply an alkali-resistant primer or block filler. Cover with latex house paint. If an exterior latex masonry paint is used as the topcoat, priming is not necessary.

To prevent recurrence of efflorescence on interior walls, the exterior walls should be sealed with a high-quality masonry coating. Waterproof coatings help seal exterior masonry walls.

Note: Extraneous water sources must be removed before painting (e.g.,

water migration at ground level, which is often caused by poor drainage).

Chalky or crumbly masonry surfaces can be primed with clear phenolic coatings (e.g., silicone sealer) to bond and seal old masonry.

This article was prepared by: Vancouver’s Best Painters:  Painters painting in the Vancouver and greater Vancouver area:  call: 604-PAINTER