Three conditions must exist before efflorescence will occur. First, there must be water-soluble salts present somewhere in the wall. Secondly, there must be sufficient moisture in the masonry to render the salts into a soluble solution. Thirdly, there must be a path for the soluble salts to migrate through the surface where the moisture can evaporate, deposit the salts and then crystallize. If any of these conditions is not present, efflorescence cannot occur.
Efflorescence is soluble salts traveling through masonry walls.
Solutions to solving efflorescence problems should focus on eliminating the source of moisture into the structure. In chimneys there are three major sources of moisture. Poorly bonded or improperly filled mortar joints and faulty flashing are common sources of rainwater penetration as well. Another source of moisture that commonly occurs in masonry chimneys is condensation. Water vapor, a natural byproduct of the combustion process, can often migrate through a system and condense within the wall.