Keeping Efflorescence Away

John Robert D. General, RN, MSN

Efflorescence is the stubborn problem that has caused bewilderment and trouble for masonry since the first time it appeared thousands of years ago on ancient masonry walls. Efflorescence is normally the white, powdery scum that can appears on masonry walls after construction but can also be brown green or yellow, depending on the type of salts. Nobody likes it, nobody wants it on their walls, but occasionally this persistent problem appears.

Great deal of effort, time, and money has been spent trying to solve the difficulties efflorescence creates. Many test programs have been developed and numerous attempts have been made to eliminate the efflorescence problem. Unfortunately, nothing has proven 100% effective against this very obstinate problem. However, even though no certain cure has been developed, a tremendous effort has been learned about how efflorescence works and ways to prevent and remove it.

Efflorescence is a type of discoloration. It is a deposit, usually white in color that occasionally develops on the surface of concrete, often just after a structure is completed. Although unattractive, efflorescence is usually harmless. In rare cases excessive efflorescence, within the pores of the material, can cause expansion that may disrupt the surface.

The formation of these salt deposits is not a mystery. They are, for the most part, water-soluble salts that come from many possible sources to mar and destroy a beautiful and serviceable masonry structure. Efflorescence is caused by a combination of circumstances: soluble salts in the material, moisture to dissolve the salts, and vapor transmission or hydrostatic pressure that moves the solution toward the surface. Water in moist, hardened concrete dissolves soluble salts. This salt-water solution migrates to the surface by vapor transmission or hydraulic pressure where the water evaporates, leaving the salt deposit at the surface. Particularly temperature, humidity and wind affect efflorescence. In the summer, even after long periods of rain, moisture evaporates so quickly that comparatively small amounts of salt are brought to the surface.

How do we then resolve these tarnishing deposits? The following tips to prevent their occurrence may be helpful.

  1. Proper selection of ingredients: Using ingredients which have minimum quantities of salts (e.g. ensuring clean sand is used) can reduce the potential for deposits. The use of tools and mixers should also be well cleaned and free from rust.
  2. Right control of moisture: Masonry should be covered with polythene sheeting. Mortar joints that are exposed to weathering should be tooled to produce a smooth weather resistant surface. It is also important to minimize premature drying when curing by avoiding exposure to wind and excessive temperature immediately after casting.
  3. Appropriate surface treatment: The use of water repellent material such as silicone will restrict the entry of water and may reduce the chance of efflorescence. However, water-repellent material may prevent moisture escaping and cause problems such as crystallization of excessive salt beneath the surface which will trigger flaking within porous and soft masonry.

In cases wherein, deposits have already become visible, then appropriate interventions may be instituted to remove them and ensure that no other result is left unaided. Here are some valuable tips to think about when planning to remove the stains.

  1. Doing a dry brushing with a stiff-bristled brush immediately after deposition. Using water in conjunction with brushing may cause salt deposits appearing again. Repeat dry brushing is an ideal treatment for eliminating this forming of efflorescence.
  2. If the efflorescence is caused by soluble alkali salts, the salts will dissolve in water applied to the structure and migrate back into it. These salts would then reappear on the surface as the structure dries up again.
  3. Another way is to utilize is muriatic acid or hydrochloric acid with subsequent flushing with water. Care must be taken because when acid is applied to brick masonry without previous wetting, it may cause "burning" or discoloration of the brick and may also eat into the mortar.

Efflorescence is a fairly controllable condition. Although efflorescence sounds and seems good, its effects to masonry are always detrimental. Breaking the factors necessary for the development of efflorescence can be done with good planning, correct supplies materials and quality construction.