[1]    [2]

Efflorescence is the a change on the surface of a material to a powdery substance upon exposure to air, as a crystalline substance forms through the loss of water [a]. This crystallization usually appears on masonry or concrete structures as a white powder. This powder is salts left behind when water evaporates from the masonry.

Three conditions must exist in order for efflorescence to occur [a].
1. There must be water-soluble salts present somewhere in the wall.
2. There must be sufficient moisture in the wall in order to render the saline solution.
3. There must be a path for the solution to migrate to the surface of the wall where it can evaporate and leave behind the salts that crystallize to create efflorescence.

Efflorescences can occur in natural and built environments [b]. In built environments, efflorescence can occur as a cosmetic problem, but if left unchecked, can lead to serious structural problems. The salts can begin to react with the cement causing an Alkali-Silica Reaction (ASR) which makes the cement dissolve.

Potential efflorescent problems can be greatly reduced by using low alkali cements, clean washed sands and clean, potable salt free water. Special admixtures can also greatly reduced the risk of concrete, masonry, and/or cement contracting efflorescence.