Stucco, brick, and other masonry surfaces may develop a white powdery substance on them known as efflorescence.

You can brush away this powder with a wire brush, but unless you eliminate the cause, it will return—and it’s existence may indicate that more serious moisture damage may occur. Efflorescence can be caused by heavy moisture in your climate or by moisture from poor drainage, roof leaks, sprinklers, and the like that penetrates walls and other masonry surfaces.

You can clean efflorescence by washing it and scrubbing it with a brush. If the surface is grimy, use a little trisodium phosphate (TSP) in warm water. Be sure to rinse away all the TSP as it may leave a residue or stain.