Definition of Efflorescence
Efflorescence is a fine, white, powdery deposit of water-soluble salts left on the surface of masonry as the water in the wall evaporates. The formations of these salt deposits, for the most part, come from the exposure to salt-bearing groundwater. Once the moisture reaches the surface, it evaporates and deposits the salt. Since most concrete masonry is somewhat porous, evaporation of the salt bearing water usually takes place before reaching the surface when exposed to a dry atmosphere when humidity is low. However, when the humidity is high and water evaporation is slower, there is more opportunity for efflorescence to grow.
Sources of Efflorescence
The movement of groundwater into building foundations and walls by capillary action, or wicking, upwards into masonry, stucco or concrete, is very often the cause of efflorescence. Another potential source of soluble salts is clay products, such as building brick and face brick. Different types of mortar have also been known to contain high concentrates of salt. The use of low alkali cement in mortar and grout will minimize efflorescence, at least from this source.
Removal of Efflorescence
There are several methods that have been suggested for the removal of efflorescence. One is to do a high pressure wash with a power washer. Construction sources also suggest the use of light sandblasting for removal of the unsightly salt deposits. If the problem persists, the application of a mild acid solution will do the trick. These acids include vinegar (5% acetic acid), muriatic acid, or even citric acid (Muriatic acid is very dangerous and should only be handled by a professional with proper safety gear). After acid washing, the surface should be rinsed thoroughly and neutralized with baking soda (sodium bicarbonate) or an equivalent neutralizing agent.
Prevention of Efflorescence
Unfortunately, very few measures can be taken to prevent efflorescence. Only vapor barriers can avert the movement of moisture from the groundwater to the surface of the concrete. Once the masonry is cleaned and free of moisture, the application of sealers and waterproofing coatings have proven to be the best method to preventing water-soluble salt from penetrating the concrete surface. If you are having problems with efflorescence contact the pros at MTS Painting. Our painting craftsmen have the tools and knowhow to get rid of this unsightly nuisance.