Efflorescence in masonry walls appears as a fluffy crystalline powder, often white, resulting from water-soluble salts within the masonry or mortar. When water penetrates the masonry, it dissolves these salts and brings them to the surface, where they are deposited upon evaporation of water.

While initial efflorescence is common post-construction and can be cleaned with water and a brush, in certain instances, efflorescence can reappear and gradually diminish over time as salts are leached out from the masonry surfaces when exposed to natural agents such as rain. However, efflorescence appearing on masonry surfaces in the later years of completion of construction indicates new water leaks. In such cases, the source of the water leak must be identified and repaired.

Efflorescence can be prevented by using masonry units tested for the absence of soluble salts and employing clean mortar ingredients. Minimizing the water intrusion into the masonry surfaces also reduces efflorescence. This is done by ensuring adequate roof drainage and providing sheltering roof overhangs wherever feasible. Also, applying coatings on the wall that prevent moisture ingress without impeding the outward movement of water vapor prevents efflorescence. In some cases, cavity wall construction may be preferable to solid wall construction, providing an additional barrier against moisture intrusion.