| Efflorescence |
EFFLORESCENCE IN CONCRETE, STUCCO, MASONRY, & BRICK
The most common cause of peeling, shaling, spalling, and white stains on surfaces composed of mortar, brick, block, concrete, and stucco is efflorescence. Soluble salts are contained in these materials. When dissolved by water, they will be carried to the surface and will remain there after the water has evaporated. These crystallized salts erode the surface.
 After stucco repair, texture coating, and trim paint |
EFFLORESCENCE - CAUSES, REMEDIES, AND PREVENTION
Efflorescence is a crystalline deposit on surfaces of masonry, stucco or concrete. It is whitish in appearance and is sometimes called "whiskers". Efflorescence has been a problem and a controversial subject for many years.
How Efflorescence Forms
Migration and formation of these alkaline salt deposits are not mysterious. For the most part, they are water-soluble salts that can originate in many sources. Water must be present to dissolve and transport salts initially. For water to carry salts to the surface, there must be channels (no matter how microscopic) through which water and dissolved salts can move and migrate.
 Before stucco repair, texture coating, and trim paint |
The denser a material, whether it be brick, stone, stucco or concrete, the more difficult it is for water to transport salts to the surfaces. The less dense a surface, the greater the likelihood of efflorescence.
Salt-bearing water, upon reaching a structure's surface, evaporates, leaving the salt deposits. When humidity is low, this salt-bearing water may evaporate before reaching the surface, leaving the salts deposited beneath the surface, unseen. Growths of efflorescence "whiskers" have been noted projecting as much as a half-inch beyond the surface on which located. On stucco and painted surfaces, efflorescence manifests itself as spalling and peeling.
A Seasonal Cycle
Since humidity has a significant effect on whether or not the salts appear, it can be concluded that efflorescence is a seasonal problem. The intensity of efflorescence development increases during and after rainy seasons. Generally, during the dry periods of spring and summer, the spalling and peeling are visble. This cycle may repeat for months or years.
The means by which efflorescing salts are carried to structure surfaces by moisture and capillary action through porous materials is understood. The amount and nature of salts deposited varies considerably depending on the character and source of the soluble salts.
Composition of Efflorescence
Efflorescence as a problem has been studied and reported for more than 100 years. The reports agree that efflorescence originates from more than one source and may be comprised of more than one or two compounds.
A bulletin by T. Richie, issued by the Division of Building Research of the National Research Council, Ottawa, Canada, states, "the following compounds are found in efflorescence."
- Sodium sulfate
- Potassium sulfate
- Sodium carbonate
- Calcium sulfate
- Sodium bicarbonate
- Calcium carbonate
- Sodium silicate
- Magnesium sulfate
There are additional salts such as chlorides, nitrates, and salts of vanadium, chromium and molybdenum, varying in significance. These last, particulary vanadium, are said to produce green efflorescence on white or buff burned clay units; while other salts produce white or gray deposits.
Sources of Efflorescence
Some alkaline salts are more water-soluble than others and they come from many sources. Movement of ground water, for instance, into building foundations and by wicking upward into masonry, stucco or concrete often causes efflorescence or spalling.
 Before stucco repair and exterior painting |
Where soil conditions indicate presence of water-soluble sulfates, precautions should be taken to prevent passage of this sulfate-bearing water to the structure. See recommendations for prevention of water infiltr5ation into the structure.
Low absorption is the best insurance against efflorescence. Properly graded aggregates, low water-cement ratio, good compaction and proper curing techniques assure portland cement products of maximum density and lowest water absorption.
Sand and gravel in their natural state may have been exposed to salt-bearing water or soil. Most rock, sand and gravel plants conscientiously wash their materials so that any contribution to efflorescence from this source has to be considered negligible.
Mixing water used for mortar, stucco or concrete from a source, which may have been in contact with sulfate-bearing soil, can lead to efflorescence. Adherence to a low water-cement ratio formula and good work practices help reduce appearance of salts from this source.
Today's manufacture of these products generally employs a procedure of washing soluble salts from the base material and adding a barium salt such as barium carbonate to the product. This reacts with calcium that may be present. In the reaction, the products are two fairly insoluble compounds - barium sulfate and calcium carbonate. Produced this way, these products have little tendency to effloresce.
 After stucco repair and exterior painting |
Masonry building products must be stored in a dry place off the ground to prevent absorption of moisture or dampness from soil, which may contain efflorescent-developing salts.
Since stucco, concrete and other masonry are somewhat porous, evaporation of the salt-bearing water usually occurs before reaching the surface when exposed to a dry atmosphere. The hydroxides are converted by reaction with the carbon dioxide of the air to alkali and calcium carbonates. Efflorescence in the form of alkali chlorides and sulfates is formed when the structure is surrounded, exposed, or in contact with salt bearing water or soil and appears as columnar or whisker-like crystals. In the case of stucco, spalling will occur.
Some sources of water-soluble salts have been covered. These may be deposited on stucco, masonry or concrete walls as efflorescence. Practically any building material in direct contact with the earth is a potential for water-soluble salts. This fact has been recognized by building materials producers, and steps have been taken to reduce their appearance to a substantial degree.
Remedies for Efflorescence
Several methods for efflorescence removal may be of value. One is to apply water under pressure. Another is acid and subsequent flushing with plenty of water. Acids more effective for this purpose are muriatic or phosphoric. Phosphoric acid has the advantage of being less corrosive relative to fumes. Fumes from muriatic acid may attack plated metal and destroy the plating. Dilute solutions (in the range of about 5% of acid to water) are appropriate for efflorescence removal.
Acid applied to brick masonry without previous wetting can cause "burning" or discoloration of the brick. It can also eat into the mortar.
Many procedures have been used to remove efflorescence from masonry, concrete and stucco. It has been found that, when efflorescence is caused by soluble alkali salts, the salts will dissolve in water applied to the surface and migrate back into it. Later blasting and chemical treatment, however, have been found to be satisfactory for removing efflorescence from the face of concrete structures.
If the coating is largely calcium carbonate or calcium sulfate, it adheres rather strongly and is difficult to remove. The practice developed in this case for masonry surfaces has been to saturate the structure as thoroughly as possible with water and then wash with dilute muriatic or phosphoric acid, followed by an immediate alkaline wash, then rinsed with plain water.
Acid-water formulation should be 5 parts acid to 100 parts water, or 20 parts vinegar to 100 parts water. A suitable alkaline wash would be diluted household ammonia.
Care must be taken applying acids to portland cement products. Acid attacks not only the calcium carbonates and calcium sulfate efflorescence, but attacks other calcium compounds to produce calcium salts such as calcium chloride. It is essential that any acid be neutralized with an alkaline rinse before it can attack other compounds.
Preventing Recurrence of Efflorescence
Summary: Efflorescence is a problem that has been studied for many years. There are several identifiable sources responsible for origin of these salts which are taken into solution by water, transported and deposited on surfaces through subsequent evaporation of the water in which they are dissolved.
Movement of this salt bearing water is controlled to some extent by weather and porosity of the material.
When the structure is built, precautions should be taken to select:
- Materials with low potential efflorescing salt content.
- Materials with low water-cement ratio.
- Proper application and curing techniques.
- Proper moisture barriers.
- Quality workmanship.
Building design should be such that a maximum of protection is assured against excessive dampness. Protective sealant coatings have been employed mainly to prevent water penetration or moisture entry of exterior walls. They will not, however, stop wicking and capillary action.
However, sealing the surfaces and preventing normal movement of these salts can cause a potentially disruptive buildup beneath the surface. Precautions should be taken in the selection of sealers as they may interfere with the wall's ability to "breathe". It is recommended that their use be restricted only to experienced applicators familiar with the materials, and manufacturers should be consulted for recommendations on proper use of their products.
There is a tremendous difference in sealers and coatings, and what results they provide, if any. This can be done readily and needs only a very little consideration to develop facts.
Recommendations to Control Efflorescence
- Ground water must drain away from the structure.
- Hose bibs should not be dripping and sprinklers should be directed away from the structure.
- Proper ventilation of the structure. (Exhaust vents through the roof, not in the attic). Prevent moisture from venting through the walls, which will result in paint, stucco and framing damage. The walls must have proper vapor barriers.
- Install rain gutters and downspouts so that the water will drain away from the structure.
- When no weep screed is present you may want to install one and/or seal the exterior walls to the foundation with tar or hydraulic cement.
- When painting stucco, consider using an epoxy fortified acrylic primer as a base coat.
- For a stucco finish coat a high quality elastomeric coating system is recommended.
