Brick With Efflorescence
Efflorescence is a crystalline salt deposit on the surface and in the pores of concrete, masonry, and other building products. A phenomenon reported as early as the 1870's and much studied since, it can appear as sulphate and carbonate compounds of sodium, potassium, calcium, magnesium and aluminum. Chlorides may also occur as efflorescence. This is usually a result of the use of calcium chloride as a mortar accelerator or the contamination of masonry components (including sand) by sea water.

There are several sources for efflorescence:

The movement of groundwater that moves upwards, by capillary action or wicking, into masonry or concrete materials.

Salts in the soil that are in contact with paving can migrate above grade.

Natural-state salts that are found in mortar, concrete, or other building products. Although rare, some raw material used to make clay brick contain small amounts of salt. However, these small amounts are minor compared to studies that found two to seven times as much soluble material in concrete products versus fired clay material. W. E. Brownell concluded in his research study that the most common form of efflorescence comes from the migration of free-alkali solutions from the mortar to the brick.

Fluorescing salts dissolve in water and are absorbed into the masonry pores. Typically, clay bricks can absorb 5% to 8% of their weight in water. Heat from the sun (or other source) begins to draw the moisture to the wall surface and as the water completely evaporates, the salt deposits are left on the surface.

Over a number of years, lime (calcium hydroxide) in the efflorescence gradually reacts with carbon dioxide in the air (carbonation), forming calcium carbonate (CaCO3). While this can be a very slow and tedious process, we have enjoyed great results in its removal.