The deposit of crystallized salts on the outer surface of masonry results in efflorescence. The deposit is usually white but may take on the color of salts or impurities present in mortar, brick, stucco, or other masonry materials. The salts are dissolved by moisture in the wall; the solution of salts and water moves to the outer surface and, as the water evaporates, the salts form a deposit. Owing to the excessive amount of water in mortar and the large amount of salts in new materials, efflorescence is more often found on new masonry work. As a building becomes older, the accumulation often disappears without having to be removed. It is usually found in places where the wall is subjected to frequent wetting—below window sills and copings, near gutters and downspouts, or where there is leakage. A prolonged wet spell may also bring out efflorescence in other places.
Efflorescence may sometimes be removed by brushing the spots vigorously with a stiff fiber or wire brush. If satisfactory results are not obtained, an acid wash should be prepared composed of 1 part of muriatic acid and from 6 to 10 parts of water. In mixing the solution, pour the acid very slowly into the water. Care should be exercised in the use of muriatic acid; it is harmful to the skin and particularly to the eyes. When using, it is advisable to wear glasses and gloves. Should the acid come in contact with the skin, it can be removed by the use of large quantities of fresh water.
The spots that show efflorescence should be scrubbed well with a fiber brush dipped in the acid solution. Avoid mortar joints as much as possible during the scrubbing process and, when the work is finished, rinse the surface of the wall with clear water. It is advisable to wash the surface again with a diluted solution of ammonia (1 pint of ammonia to 2 gallons of water) to remove every trace of acid. The deposits may reappear from time to time and require additional washings, but will disappear entirely when the supply of soluble salts in the materials has been exhausted.
Because efflorescence is caused by the evaporation of water which . has previously been absorbed, it is important that opportunities for absorption be reduced as much as possible if the trouble is to be checked. It is well to examine gutters and downspouts for leaks and to see that window sills and copings have drip grooves cut along the underside to prevent water from running down the face of the wall. If conditions are unusually bad, and it is felt that the expense is warranted, there are a number of colorless waterproofing compounds that may be applied to the surface of the wall to check absorption and thus tend to eliminate the formation of efflorescence.