What can be done to minimize efflorescence in masonry walls?
Efflorescence is caused when water enters masonry walls and dissolves soluble compounds in the brick, the mortar or both. These compounds move to the surface of the masonry as the water slowly evaporates. Efflorescence is generally worse when water is held within the masonry walls for long periods of time. This allows more soluble compound to go into solution and migrate to the surface. Less efflorescence occurs in areas that dry rapidly. In order to reduce the likelihood that efflorescence will occur, you must restrict the amount of water that penetrates and is held within the masonry walls, or you must reduce the available salts and soluble compounds in the masonry units and mortar. For clay brick units, the efflorescence test in ASTM C 67, "Standard Test Methods for Sampling and Testing Brick and Structural Clay Tile" should be used. The units should be rated as "not effloresced." In this test, the units are partially immersed in distilled water to a depth of approximately 1 inch for seven days. No efflorescence should be noted within 10 feet of the sample under an illumination of not less than 50 foot-candles. Proper wall construction and details will prevent water from penetrating the masonry walls. Flashing should be used in any areas where water may otherwise be able to penetrate the top of walls, such as sills below windows and copings along the tops of the walls. Cracking should be avoided in masonry walls by providing proper support for masonry walls both for lateral loads and gravity loads and by providing appropriate movement joints in masonry. The mortar joints in the masonry should be well-compacted, generally with the use of concave or V joints.