With the rain we’ve been having, water is on the move! We see the evidence in concrete and block walls, where the water evaporates, and leaves a white powder behind:
A. Efflorescence is a condition where white (salt) deposits form on the surface of the masonry. The formation of salts is usually a sign of excessive amounts of moisture in the masonry. Salt deposits on the masonry surface may develop from:
- Soluble compounds within the masonry or in the soil.
- In the presence of water, these compounds gradually migrate to the wall surface, where they remain when the water evaporates.
- These types of surface deposits are water soluble and can usually be removed by washing the wall with water from a garden hose supplemented by scrubbing with a stiff bristle brush.
- Improper or insufficient rinsing of masonry after chemical cleaning or repointing.
- The penetration of rain into the masonry through deteriorated mortar joints and other failures in exterior envelope (lack/failing flashing, expansion joint caulking missing, etc.).
- Exposure to air pollution, which can result in the formation of thick sulfate (salt) crusts on the underside of moldings and eaves, areas not regularly washed by rainfall.
- Capillary movement of moisture through masonry, the drying out of walls associated with a damp proofing treatment or the elimination of a ground water source may increase the amount of salt at or near the wall surface.
B. These deposits are generally not harmful to the building, just unattractive. However, they should be washed from the surface as soon as possible. Some salt deposits are water-soluble for only a brief period after reaching the atmosphere. Carbon dioxide in the atmosphere eventually converts these salts into water-insoluble carbonates, which are impossible to remove without the use of acids.
More on removing it: