The unsightly appearance of efflorescence usually has no effect on masonry's structural integrity or durability. Efflorescence can be very complex; however, a basic understanding of its causes can lead to preventive measures and can aid in the elimination of the problem. Efflorescence can be removed from the wall with proper cleaning techniques and, in most cases, will take care of itself with time.
When three conditions exist, salts precipitated on the evaporation surface form white, brown, or green stains:
- There must be soluble salts in the wall.
- There must be a source of water in contact with the salts to form a salt solution.
- There must be a pathway for the salt solution to migrate to a surface and evaporate.
It is virtually impossible to construct a masonry structure without some soluble salts and water in the wall. Therefore, the potential for efflorescence exists in all masonry structures.
Many construction materials contain soluble salts. Portland cement contains sodium and potassium alkalis. If the free alkali in the portland cement is greater than 0.1%, there is a potential for "new building bloom." When portland cement hydrates, the calcium hydroxide formed can also contribute to efflorescence.
Fired clay products can also contain soluble salts but usually less than 0.1%.
No method has been developed to test for efflorescence from mortar.
Other possible sources of soluble salts in the wall are contaminated construction water, contaminated mortar sands, mortar additives, fertilizers, and deicing salts. Chemical reactions within the wall resulting from brick-mortar reactions, acid rain, and chemical cleaning can also produce soluble materials.
A masonry wall cannot be built without water. Mortar, concrete, and grout require water. More water in mortar improves its workability, which enhances its bond with the units. Cleaning new masonry adds large quantities of water to the walls. This construction water can take months or years to totally evaporate from the wall surface.
Rain becomes a major source of water if there are leaks in the wall. A wind-driven rain can penetrate the face of a masonry wall or even climb a wall.
Where a brick rowlock coping is used, the design is critical because of the many mortar joints. A brick rowlock coping without flashing beneath will nearly always lead to efflorescence.
Condensation can also be a source of water in a wall. The proper use and construction of vapor barriers can minimize this problem.
Salt solutions must migrate to the evaporation surface to create efflorescence. Cavities clogged with mortar droppings can serve as a bridge for moisture migration. Material porosity can also contribute to moisture migration.
Some efflorescence cannot be avoided, but certain precautions can be taken to minimize the problem:
- Select and specify high-quality materials for construction.
- Design walls with flashing and weep holes at the base of the wall and above and below all wall openings.
- Good workmanship is a top priority in preventing problems.
- Walls should be cleaned properly.
When efflorescence already exists, several questions should be asked and steps taken to address the problem:
- Determine the age of the building.
- Collect a sample of the efflorescence and store it in a sealed container for chemical analyses.
- Look for patterns in the efflorescence on the wall, and take pictures for reference.
- Study the construction details from the design drawings.
- Inspect the wall, noting the presence or absence of weep holes and flashing.
- Check the condition and soundness of mortar joints.
Any and all construction flaws must be corrected before attempting remedial cleaning. Efflorescence can be removed by dry brushing, brushing with a wet brush, spraying with low-pressure water, or applying a mild solution of hydrochloric acid. There are also many proprietary cleaners available to remove efflorescence and stubborn stains if the simple procedures are unsuccessful.
Efflorescence is seldom desirable. But in older buildings it can serve as a cry for help, indicating and helping to pinpoint water intrusion. The problem should be addressed as soon as possible to avoid more serious problems such as corrosion and freeze/thaw damage.
Article includes a chart listing sources of salts and water, and possible lines of defense.