Masonry Magazine June 1995 Page. 30
Most efflorescence can be classified as temporary. Often termed "new building bloom", indicating its link to the exposure conditions and excess moisture that accompany new masonry construction, it is harmless and should not cause undue concern. Recurrent efflorescence on the other hand indicates a chronic moisture problem. Efforts should be taken to prevent and eliminate recurrent efflorescence. The following recommendations are targeted toward that goal:
Prevent inadequate hydration of cementitious materials caused by cold temperatures, premature drying, or improper use of admixtures.
Tool all mortar joints with a V- or concave-shaped jointer to compact the mortar at the exposed surface and create a tight bond between mortar and masonry unit. Weeping, raked, and untooled struck joints are not recommended in exposed applications.
Assure that mortar joints are properly filled. Deteriorated or defective mortar joints should be repointed to keep moisture out of the wall.
Limit entry of water and provide for quick exit by giving proper attention to design details for correct installation of waterstops, flashing, weepholes, and copings.
Maintain clean cavities and unobstructed weepholes during the construction of cavity walls.
Apply paint or other proven protective treatment to the outside surfaces of porous masonry units.
Install vapor barriers in exterior walls or apply vaporproof paint to interior surfaces and use designs that minimize condensation within masonry.
Carefully plan the installation of lawn sprinklers or any other water source so that walls are not subjected to unnecessary wetting.
If feasible, use wide overhanging roofs to protect walls from rainfall.
Provide for pressure equalization between the outside and the void within the masonry wall by appropriate venting of cavities.
Clearly, the design and construction of weather-resistant masonry is key to eliminating recurrent efflorescence. For a more complete discussion on preventing water penetration of masonry construction see PCA publication IS220, Building Weather-Resistant Masonry Walls.
To reduce the potential for efflorescence associated with new construction, the following steps may be taken to limit the moisture introduced into the wall during construction and reduce the level of efflorescing salts:
Keep masonry units stored at job site covered and on pallets placed in well drained locations.
Cover the top course of masonry at the completion of each day's work, particularly when rain is expected.
Use washed ASTM C144 sand.
Don't use units known to effloresce while stockpiled.
Use brick that pass the ASTM C67 efflorescence test.
Use clean mixing water free from harmful amounts of acids, alkalies, organic material, minerals, and salts. Do not use seawater or brackish water for mixing mortar.
Use insulating material free of salts when walls of hollow masonry units are to be insulated by filling the cores.
Be certain that mixer, mortar box, mortarboards, and tools are not contaminated or corroded. Never deice this equipment with salt or antifreeze material.
Use mortar materials of lower alkali content.
Note that "reducing moisture content of masonry" does not mean arbitrarily reducing the water content of mortar or allowing walls to prematurely dry out. Both of these measures will contribute to increased permeability of the masonry construction and thus increased potential for recurrent efflorescence.
Removal
Since efflorescence often occurs during or immediately following construction, the first impluse is to immediately wash it off with water or a masonry cleaning solution. This is not advisable, particularly in cool or cold damp weather when the primarly result of such action will be to introduce more water into the masonry wall. As previously noted, given time, the efflorescence will often disappear by itself or at most may require mild cleaning measures such as dry brushing or rinsing and brushing with a stiff brush. If this is not satisfactory, it may be necessary to wash the surface with a proprietary masonry cleaning solution or a very dilute solution of muriatic acid (1 to 10 percent).
Prior to using a proprietary cleaning solution or muriatic acid solution, the compatibilty of the proposed solution with the masonry units should be verified with the manufacturer of the units. Where integrally colored concrete masonry units or mortars are involved, use only a 1 to 2 percent acid solution or a proprietary cleaner specifically recommended for that application. In any event, care should be taken to assure that the cleaning solution and technique do not etch the surface of masonry units or mortar joints. Improper cleaning can significantly change the appearance of the masonry, damage mortar joints and units, and contribute to additional efflorescence or staining.
It is often helpful to determine the type of salt in the efflorescence so that a cleaning solution can be found that readily dissolves the efflorescence without adversely affecting the masonry. Before any treatment is used on any masonry wall, the method should be tested on a small, inconspicuous area to be certain there is no adverse effect. In cases involving recurrent efflorescence, the source of moisture should be determined and corrective measures taken to keep water out of the structure prior to attempted removal of the efflorescence.