Masonry Magazine October 1986 Page. 29
Efflorescence Control
Cleaning agents are proprietary and must be used according to the manufacturer's directions. Generally, thorough pre-soaking and post-washing with clean potable water is required. Presoaking is done to saturate the wall, reducing its natural porous tendencies and limiting the depth of penetration of the cleaning solution.
After the cleaning solution has been used, the wall must be thoroughly washed with clean water to remove any of the cleaning chemicals. This is very important since most cleaning agents are acidic in nature and cannot be permitted to remain in the wall where they will continue to react with and erode the masonry itself.
A conventional chemical cleaner that has been used for efflorescence control is muriatic acid in a mild solution, usually one part muriatic acid to 12 parts water. Several mild individual applications are better than one overpowering dose. Again, care must be taken to thoroughly presoak the wall with clean water and to thoroughly flush the wall of all remaining acids with clean water.
If the efflorescence is in small patches or limited areas, hand washing with a mild detergent and a stiff bristle brush will often prove sufficient.
After sandblasting or acid cleaning the efflorescence from the masonry, the wall should be sealed. The efflorescence already indicates that soluble alkali sulfates exist in the wall and that the sulfates have migratory paths to the surface. All we can prevent now is the moisture from entering the masonry and rendering the sulfates into solution.
Care must be taken not to trap the salts below the surface of the masonry. If the salts are stopped just below the surface, for instance by a silicon water repellent, the water will still evaporate, depositing the salts behind the surface, which then crystallize. The expanding salt crystals can then cause spalling and small flakes to pop off the wall.
It is not a cure-all to simply seal a wall when efflorescence already exists. The presence of efflorescence shows that the salts are already in the wall, have sufficient water to be made soluble, and that migratory paths exist for the salt solution to travel through to the surface. It would be better, if possible, to wait until the efflorescence problem has been reduced to a minimum before sealing the wall.
Efflorescence is a controllable condition that should not be a problem in modern masonry. Breaking the chain of conditions necessary for efflorescence can be done with good details, the correct materials, and quality construction.
Related Material
"BIA Technical Notes on Brick Construction," Brick Institute of America: Note 23 Revised, "Efflorescence Causes and Mechanisms": Note 23A Revised, "Efflorescence Prevention and Control."
"Reinforced Grouted Brick Masonry Construction," Masonry Institute of America, Los Angeles, Calif.
"Investigation of the Source of Efflorescence of Brick Masonry," Donald W. Bolme and Lester P. Berriman, Stanford Research Institute, Clay Products Promotional Fund, 1960.
"The Causes and Control of Efflorescence on Brickwork," Wayne E. Brownell, Structural Clay Products Institute, 1969.
"Investigation of Methods for Reducing Efflorescence of Masonry." James M. Ross and Lester P. Berriman, Stanford Research Institute, Clay Products Promotional Fund, 1961.
"Fundamental Factors Influencing Efflorescence of Clay Products," W. E. Brownell, The Journal of The American Ceramic Society, Dec. 1949.
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MASONRY-SEPTEMBER/OCTOBER, 1986 27