| Efflorescence is a fine, white, powdery deposit of water-soluble salts on the surface of masonry or in the pores of masonry. The most common salts are sulfate and carbonate compounds of sodium, potassium, calcium, magnesium and aluminum, although others exist.
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| The primary effect or objection is the appearance of efflorescence on the surface of masonry, both clay and concrete. It can be a serious visual defect. However, under certain conditions, salts deposited below the surface of a masonry unit can cause cracking and spalling due to forces generated by salt crystallization. This can further degrade appearance, but has the more serious effect of reduced structural properties.
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| The main source of salts is the portland cement used in mortar and grout. Other sources can include the masonry units, sand used in mortar and grout, and the water. Hydrated lime used in mortar does not generally contribute to efflorescence.
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| Water-soluble salts are brought to the surface of masonry in solutions of water and deposited there by evaporation. The salts solution may migrate across the surfaces of the units or through the pore structure of the masonry units.Therefore, the conditions which lead to efflorescence are:
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| (1) A source of soluble salts must be present.
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| (2) A source of water to dissolve the salts must be available.
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| (3) The water must be in contact with the salts for a sufficient time to dissolve them and carry the solution to the masonry unit surface and into the pores of the units.
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| Because the salts must be in solution to cause efflorescence, the obvious solution is to prevent the intrusion of water. This is difficult during construction because of the water present in mortar and grout. During construction, partially completed masonry elements and all on site masonry materials should be protected to minimize waterintrusion from rain, snow or other sources.
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| The most critical item in preventing efflorescence is providing good masonry details that will prevent water penetration into the completed masonry construction. The design and details of the structure, of which the masonry components are a part, should be such that water exposure and penetration of the masonry will be minimal. Overhanging eaves, capping of walls, copings, sealants, flashing, and tooling of mortar joints are examples. Equally important is the maintenance of these features.
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| Efflorescence occurring during or just after construction may disappear with normal weathering. If not, the following cleaning methods may be done in ascending order doing the least necessary to achieve the desired result.
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| (1) Dry brushing may remove most efflorescence
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| (2) In warm, dry weather washing may be used, but it should be realized that washing requires the use of water which may bring more salts to the surface
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| (3) Chemical cleaners are available such as a 1:12 muriatic acid solution. Use requires presoaking to limit the depth of penetration of the solution and thorough washing afterwards to remove all traces of the solution.
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| (4) Sandblasting has been used but is not recommended because of its damaging effect on mortar and unit surfaces.
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