Cleaning Masonry

Used with permission from:
Masonry Institute of British Columbia
W.C. (Bill) McEwen P.Eng.
Executive Director

One of the final steps in the completion of a successful masonry project is the cleaning of the walls. Different cleaning methods and materials are required for different brick and block units. The following notes highlight the key steps to the safe and effective cleaning of masonry. It is recommended that cleaning be included under the masonry scope of work, and that the masonry contractor be responsible for coordination and performance of this activity.

Construction Phase

The following procedures during wall construction will minimize the amount of cleaning required.

Minimize Mortar Droppings And Smears
Care and attention during installation, particularly during wet weather, can greatly reduce the amount of mortar cleaning required.
Avoid Mortar & Mud Splatter
Turning scaffold planks away from the wall when not in use and covering the lower wall or ground can prevent rain splashing material on to the wall.
Cover Wall
The tops of walls should be covered while exposed to rain. Water entering the open cores can delay wall drying and increase efflorescence.
Clean & Brush When Tooling Joints
It is much easier to remove mortar droppings at this stage, before they have hardened.
Wait For Wall To Cure Before Cleaning
Mortar joints must be allowed to fully set and cure to avoid damage from the cleaning process. One week is usually adequate.

Cleaning Phase

Dry Brushing
This procedure may be all that is required for block walls. Walls that have been kept clean during the construction phase may not require further attention. Clay brick walls should have any mortar droppings removed before proceeding to wet cleaning.
Wet Cleaning
1. Test Area:
  Initial cleaning of a inconspicuous area should be performed to confirm the suitability of cleaning methods and materials.
2. Protect Surroundings and Workers:
  Windows, building trim and other masonry materials must be protected from chemical damage. For power spray applications, a broader area around and below the wall must be considered. Workers must wear protective safety gear suitable for the materials being used.
3. Minimum Temperature:
  Cleaning materials are generally more effective when the temperature is 7 degrees (C)or warmer
4. Pre-Soak Walls
  This is a critical step in chemical cleaning. The wall should be saturated with water before application of chemicals to avoid absorption of the cleaning solution or dissolved mortar. High pressure spray should not be used for presoaking.
5. Cleaning Solution:
  Proprietary cleaners recommended by the manufacturer of the concrete or clay masonry unit should be used. Different colours of clay brick may require different cleaning solutions. Plain acid solutions are not recommended for most applications, and should never be used on coloured concrete block.
6. Cleaning Method:
  Cleaning solutions should be applied by brush or low pressure spray, and left on the wall for the time recommended by the cleaner manufacturer. Cleaning methods range from hand brushing to high pressure spray. High pressure spray should be used with caution, with a maximum pressure of 700 psi. Cleaning is normally done from the top down, but the lower wall must always be kept soaked.
7. Rinsing:
  Another key step in the cleaning process is a thorough rinsing of the wall to remove all cleaning solution and dissolved material.
8. Stains and Graffiti:
  For cleaning unusual stains or graffiti, consult local manufacturers' literature for specific treatments.
9. Construction and Maintenance Records:
  It is recommended that the cleaning methods and materials be recorded for future reference by the building owner. A suggested format for this information is included in the Maintenance Manual distributed by the Masonry Institute of B.C.

Graffiti Resistance

The effective removal of graffiti requires the use of specific chemical strippers designed to dissolve unwanted markings without negatively impacting the masonry surface. Proprietary cleaners formulated for this purpose should be used, and the manufacturers' literature consulted for specific treatments. Care needs to be exercised to avoid the use of excessive pressure or any other technique which will abrade and alter the masonry surface.

Over the last few years with the apparent increase in graffiti, there have been a variety of protective treatments developed to help reduce the penetration of the graffiti into the pore structure of the masonry. These fall into three general categories: high density polymeric films (e.g. polyurethanes), sacrificial films (e.g. acrylics), and penetrating paint repellents (e.g. modified siloxanes).

High density polymeric films are clear or pigmented coatings with extremely high chemical resistance and low porosity to resist graffiti penetration and stripping solutions. The two major disadvantages of these types of products are their low permeability (which leads to moisture entrapment behind the film) and the fact that they radically alter the appearance of the masonry (glossy appearance).

Sacrificial coatings are, as the name implies, consumed in the protection process. The major disadvantages of sacrificial coatings are that they require retreatment after stripping; they are film formers and not very vapour permeable; and they have a tendency to alter the appearance of the masonry.

The third type of protective treatment is a new, developing technology based upon chemistry which has been field tested for a number of years. The penetrating paint repellent works on a principle similar to water repellents: it alters the surface energy properties of the masonry so that graffiti has a tendency to agglomerate rather than wet into the surface. The graffiti then cures without having penetrated the pores, and can be removed relatively easily with an appropriate chemical stripper. The chemical structure of this protectant makes it inert to most chemical stripping solutions, but it does not form a continuous film which could lead to vapour permeability problems. Another advantage of this product is that it can be water based making it environmentally safe. Although some surface darkening occurs after application, because it penetrates, this effect is not as pronounced as with the high density and sacrificial coatings. This new type of treatment is expected to be introduced to the local market later this year.