Why does an efflorescence appear?
In chemistry, efflorescence is defined as the migration of a salt to the surface of a porous material, where it forms a coating. The essential process usually involves the dissolving of an internally held salt in water. The water, with the salt now held in solution, migrates to the surface, then evaporates, leaving a coating of the salt. These efflorescent salt deposits tend to appear at the worst times, usually about a month after the building is constructed, and sometimes as long as a year after completion.