EFFLORESCENCE

Efflorescence is a crystalline salt deposit on the surface and in the pours 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, contamination of masonry components(including sand) by sea water or the improper use of hydrochloric acids in cleaning solutions.

There are several sources for efflorescence: 1) the movement of groundwater that moves upwards, by capillary action or "wicking", into masonry or concrete materials. 2) salts in the soil that are in contact with paving can migrate above grade. 3) 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". This would also be true for any newly poured concrete curb, foundation or sub base slab.

Efflorescing salts dissolve in water and are absorbed into the masonry pours. 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.

Since humidity and moisture play a key role in the efflorescence process, some areas of the country will be affected more than others. Seasons will play a role as precipitation during season changes will increase the likelihood of efflorescence.

The most important solution to solving efflorescence is finding, locating and dealing with the source of water. Since the source of water in a paving application is generally clear, the most important factor in limiting the occurrence of efflorescence is insuring adequate drainage of the pavement through grading or specific drainage systems. Good drainage will keep the pavers dryer and thus, they will be less likely to effloresce.

While efflorescence control systems are available, they don't guarantee full arrest of the problem and tend to be expensive. The best thing to do is to allow the efflorescence to run its course provided that the paved area has good drainage. The main reasons for this recommendation are as follows: the source of the salt is most likely coming from base materials or mortar. In a flexible base application, after 6 months, 90 % of the water will run off the paving surface and away from the pavers versus down through the joints. This change should carry the salts in solution into the ground rather than into the pavers. In all cases, free salts dissipate eventually and the problem goes away for good, generally within 18 months.

As a general rule, the removal of efflorescing salts from the face of masonry is relatively easy operation. Efflorescing salts can be removed with dry brushing or with clear water and a stiff brush.