Efflorescence: Cause and Control1
ef-flo-res-cence (ef∋ le res∋ens), 1. a change on the surface to a powdery substance upon exposure to air, as a crystalline substance through loss of water. 2. to become incrusted or covered with crystals of salt or the like through evaporation or chemical change.
Efflorescence is the stubborn problem that has caused confusion and trouble for masonry since the first time it appeared thousands of years ago on ancient masonry walls. Efflorescence is normally the white, powdery scum that can appear on masonry walls after construction but can also be brown green or yellow, depending on the type of salts. Nobody likes it, nobody wants it on their walls, but occasionally this persistent problem appears.
Great deals of time, money and effort have been spent trying to solve the difficulties efflorescence generates. Many test programs have been developed and numerous attempts have been made to eliminate the efflorescence problem. Unfortunately, nothing has proven 100% effective against this very stubborn problem. However, even though no surefire cure has been discovered, a great deal has been learned about how efflorescence works and how to prevent it, and if preventive measures are inadequate, how to remove the efflorescence if it does appear.
This article explains the mechanics of white efflorescence, how to help prevent efflorescence and some traditional methods used to remove efflorescence from new walls.
What is Efflorescence?
We know that efflorescence is a fine, white, powdery deposit of water-soluble salts left on the surface of masonry as the water evaporates. These efflorescent salt deposits tend to appear at the worst times, usually about a month after the building is constructed, and sometimes as long as a year after completion.
Efflorescence is not a simple subject. Three conditions must exist before efflorescence will occur.
• First: There must be water-soluble salts present somewhere in the wall.
• Second: There must be sufficient moisture in the wall to render the salts into a soluble solution.
• Third: There must be a path for the soluble salts to migrate through to the surface where the moisture can evaporate, thus depositing the salts which then crystallize and cause efflorescence.
All three conditions must exist. If any one of these conditions is not present, then efflorescence cannot occur.
Even though the efflorescence problem is complex, it is not difficult to prevent.
Although no economically feasible way exists to totally eliminate any one of these three conditions, it is quite simple to reduce all three and make it nearly impossible for efflorescence to occur.
Source of Efflorescent Salts
A chemical analysis of efflorescent salts in the Southern California area (1) reveals that they are principally alkalies of Sodium Sulfates (Na3S04) and Potassium Sulfates (K2S04). These are the main soluble salts to be concerned with in Southern California since these are 90% of the efflorescence found in this area. These alkali sulfates appear because they exist somewhere within the masonry wall, either in the brick, the mortar, or the grout, or possibly a combination of these three. These alkalies combine with sulfates from the masonry to form sulfate salts. The alkali sulfates in the wall are dissolved by water into a solution which then moves through the natural pores in the masonry. The solution migrates to the surface of the wall where the water evaporates, depositing the salts on the wall and generating the white powdery scum we know as efflorescence.
Figure 1. Typical white efflorescent salts on brick and block masonry
1 Based on a technical paper written by Michael Merrigan, P.E., originally published in The Masonry Society Journal, January-June, 1986