The cause of and cleaning methods for efflorescence on brick walls. Materials needed and procedure for safely removing efflorescence.
This article explains the mechanism of efflorescence on masonry walls, how to help prevent efflorescence and some traditional methods used to remove efflorescence from new walls. See my article on How to Repoint Brick Veneer Walls at https://knoji.com/how-to-repoint-brick-veneer-walls/
Brick Efflorescence is the problem that has caused confusion and trouble for masonry since the first time it appeared thousands of years ago on masonry walls. Efflorescence is normally the white, powdery substance that can appear on masonry walls after construction, but can also be brown green or yellow, depending on the type of salts found in the wall.
Three conditions must be present for efflorescence to form, if any one condition is missing, there will not be efflorescence. The three conditions are:
1. There must be water-soluble salts present somewhere in the wall.
2. There must be sufficient moisture in the wall to render the salts into a soluble solution.
3. There must be a path for the soluble salts to migrate through to the surface where the moisture can evaporate and deposit the salts on the outer surface of the brick or block that then crystallize and cause efflorescence.
The efflorescence problem is complex, but it is not difficult to prevent. Although there is no way to totally eliminate any one of these three conditions, it is fairly easy to reduce all three and make it nearly impossible for efflorescence to occur.
Many studies have been developed and numerous attempts have been made to eliminate this problem, but nothing has proven to be completely effective against it. However, even though no surefire cure has been discovered, a great deal has been learned about how efflorescence works and how to prevent it. If preventive measures fail to eliminate efflorescence, there are some methods to remove the efflorescence if it does appear.
An efflorescence remover such as a dilute solution of Hydrochloric (also known as Muriatic) acid can be used in severe cases, but extreme caution should be taken with this chemical. Also, it is important to never seal brick that is experiencing efflorescence. You may damage the brick's surface.
The best method is to simply brush the salt deposits off the surface with a stiff broom. The use of high pressure water is not always recommended. The water can dissolve some of the salts and actually drive them back into the masonry and they can reappear when this water evaporates. In the most severe cases, dilute solutions of muriatic acid can be used. Use extreme caution when working with this acid as it can cause serious eye and skin burns. The vapors are also very toxic. Use a respirator, goggles, and rubber gloves when working with such chemicals. Full strength Muriatic acid, improperly applied to a masonry surface, can damage the brick and cause discoloration. Most popular concrete and grout cleaners on the market contain phosphoric acid. This acid will do almost as well as muriatic acid, but with less danger. Phosphoric acid cleaners also contain chemicals which emulsify oils to help the acid work more effectively and safely increase its cleaning properties.
Follow the directions on the container, but usually a mixture ranging from 1 part acid to 10 parts water to 1-to-16 is recommended.
Long-handled Masonry Brush, preferably not a wire brush
Baking Soda, ammonia or Lime to neutralize the acid
Lightly dampen the wall with a hose.
Mix the acid with water. 1 part acid to 10 parts water, but dilutions as light as 1 part acid to 16 parts water will work if the efflorescence is less severe. 1 to 16 is 1 cup acid to 1 gallon of water. Follow the recommendations on the label. Also, add the acid to the water, not the water to the acid.
Brush or spray acid onto affected area. Do not use a metal sprayer. A plastic sprayer will work for a while, but the metal components inside will eventually dissolve, so have a few extra sprayers on hand. Throw them away when finished.
Let the acid sit for no more than a few minutes--or less if you can see the efflorescence lifting.
Scrub off any remaining residue with a stiff brush while rinsing thoroughly with water.
To neutralize any remaining acid, you can spray a neutralizing rinse of one (1) cup household ammonia to one (1) gallon of water.
It may be necessary to repeat this several times until most of the salts are removed. Changes in season also accelerate the process, especially from Summer into Fall and Winter. This is due to the fact that in most areas of the country, wind-driven rain and humid conditions fill the bricks with moisture until the outdoor humidity levels drop, allowing the moisture to be pulled out to the surface.
Possible path of water-soluble salts that form efflorescence
Brick that is still experiencing efflorescence should not be sealed. If you do this, there is a possibility that you can actually damage the surface of the brick.
The sealer will block the movement of salts to the surface of the brick. The problem with this is that as the salts work their way to the sealer at the surface of the brick they stop and build up inside the brick. The concentration of the salts increases as the water evaporates. In certain instances, the salts begin to crystallize. This process of crystallization can create enormous pressure on a microscopic level that can actually cause the face of the brick to pop off or spall. This would result is a more porous surface, which will allow an increasing amount of moisture into the brick units. This may also allow flowing water to get behind the brick and cause moisture problems with the sheathing and structure of the building.
During construction of a new masonry wall, several things can be done to reduce the potential for efflorescence forming.
Using a low alkali Portland cement will often eliminate the efflorescent problem. It is recommended that low alkali Portland cement be used to reduce the chances of efflorescence occurring. Low alkali Portland cement has 0.6% alkali or less, by weight in the cement.
Check the bricks used in the wall. The natural clays used in brick often contain soluble alkali sulfates. Most modern fired-clay brick have balanced chemical additives and do not greatly contribute towards the efflorescence problem.
The next source for soluble salts would be the sand used in the mortar and grout. Contaminated sands with soluble alkali sulfates will cause efflorescence unless the sulfates are removed. Using clean, washed sand will eliminate the contribution of salts.
The water used in the mortar and grout during construction can also be a source of contaminants. Clean, potable, salt-free water must be used at all times. Most municipal water sources show insignificant amounts of salts in the water. Water from other sources should be checked for their alkali sulfate contents to be sure no efflorescing salts will be introduced into the masonry wall.
For an existing wall, check for leaking gutters or loose downspouts that allow rain to run down the brick, which may be the source of water causing the efflorescence to form. Check for gaps at the top of brick walls or flashing around chimneys that is loose or missing. Cap flashing or coping are also areas where water can get into the brick.
Efflorescence is an unsightly side effect of brick walls, but with a little effort during construction and maintenance after the wall is up can help keep your brick looking good for years to come.