Efflorescence. (Technical Briefs).

One possible indicator of moisture intrusion is a white, powdery, or crystalline substance sometimes found on the surface of concrete, plaster, or masonry. Known as efflorescence, bloom, or effervescence, it appears when water that containing soluble salts evaporates from the surface of an object. On exterior surfaces, efflorescence is usually only of aesthetic concern. When found indoors, however, it indicates a water or moisture intrusion that could amplify mold and possibly cause structural damage.

The soluble salts originate from the building materials themselves or from the ground. As water travels through soil, a wall, or a building foundation, it dissolves the salts, transporting them to the surface. When the water evaporates, it leaves the salts behind. The deposits usually are white, but they can also be green, brown, or gray depending on the mineral composition.

Efflorescence will continue as long as there is a source of salts and water. Often, the salt sources get exhausted over time, and the exterior efflorescence disappears by itself with normal weathering. For a speedier cleanup, wash the surface with water or diluted muriatic acid and a stiff brush (nonwhite efflorescence should not be washed with acid as staining could occur). Note that water can redissolve the salts and transport them back into the building material, allowing further efflorescence. Applications of acid should be preceded by a wetting of the surface and followed with a water or alkaline-and-water rinse. Be sure to consult professional guidelines before handling any acid and to follow proper safety precautions.

Interior efflorescence should be investigated immediately, as it can be a sign of groundwater intrusion, leaky pipes, defective drains, or other sources of water damage. Careful analysis of the situation is important not only to determine the cause of the water incursion, but also to determine if mold amplification has occurred. If, upon analysis, no mold is found, the water source should still be immediately removed to prevent potential future fungal growth.