cleaning masonry walls 

by Gwin R. (Dick) Whitney, Brock White Co. LLC, Duluth, MN


larger brick or CMU generally require the use of a propriety chemical

The masonry wall has been completed. The mason has been unsuccessful in convincing the owner and the architect that those mortar smears are an expression of the mason's artistic ability. What to do?

In the best of all worlds, if the wall was of clay brick, the architect has consulted with the brick distributor or manufacturer, obtained their recommendation for cleaning that particular type of brick, and included those recommendations in the specifications. If no specific cleaning information has been provided, the brick or block distributor or manufacturer should be consulted for their recommendations.

In general, dry or wet brushing to remove loose dust, sand, and larger mortar chunks can successfully clean smaller masonry jobs. Wooden paddles or other non-metallic tools may be used to remove stubborn particles. Larger brick or CMU projects generally require the use of a propriety chemical product or muriatic acid. It is my opinion that the use of a proprietary product is the preferred cleaning method for the following reasons:

  1. Muriatic acids may contain chemicals that can discolor clay brick or CMU.
  2. Muriatic acid is generally more concentrated than proprietary products, and is more likely to burn mortar joints. This increases the probability that water will infiltrate the wall system through the mortar joints.
  3. Proprietary products are sold with specific application instructions. Field assistance is available through the manufacturer.
  4. Proprietary products contain special wetting agents, which keep the material wet on the wall longer than plain acid, thus allowing the cleaning material to work longer on the mortar smears, making removal easier and quicker.
  5. Proprietary products come in a variety of formulations designed for the physical properties of the masonry being cleaned. Some clay brick contain metallic deposits such as vanadium, manganese, molybdenum, and other impurities, which, when in contact with muriatic acid, can produce green or brown stain on the surface of the masonry. There are specific proprietary products for: 
    1. Concrete burnished, break-off, and regular block and for hard-fired red, tan, and pink clay brick. 
    2. Gray, brown, white, and most light colored clay brick, which are most subject to green vanadium and brown manganese staining. 
    3. Red or dark colored hard-fired clay brick, which can stand a harsher cleaning material.

When cleaning masonry, be aware of the following:

  1. The best temperature for cleaning masonry is 70 degrees or above. For each drop of 10 degrees below 70 degrees, the effectiveness of the cleaning material drops 20%.
  2. Cleaning compounds should be tested on the masonry. Apply according to the manufacturer's instructions and dilute with water to the lowest concentration that will clean the wall.
  3. Saturate the masonry with water just before beginning cleaning.
  4. Generally, allow the masonry to cure for 14 to 28 days before cleaning.
  5. Clean walls containing colored mortar with detergent masonry cleaner.
  6. Apply cleaning material with a low-pressure (50 psi) sprayer or with a soft fibered masonry brush.
  7. Rinse with a high-pressure (approximately 400 psi) washer using 4-6 gallons per minute through a fan type stainless steel tip dispersing at a 25 degree to 50-degree fan spray. Never use a fan spray less than 15 degrees as that could etch the mortar joints or the surface of the masonry units.

For further information please refer to the Brick Industry Association (BIA) Tech Note 20 revised, or contact your masonry supplier. Concerns about environmental questions can be addressed by contacting the field representatives or the manufactures of proprietary cleaning products at their regional sales offices.

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2000 Gwin R. (Dick) Whitney, CSI 

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