Technical Information - Problems That Can Arise From Cleaning Color Units
Higher than recommended dilutions of masonry cleaner, failure to pre-wet wall before cleaner is applied, allowing cleaner to soak into wall, and failure to flush cleaner completely can all cause chemical burning as seen in lower right of this picture. Please note that the pigment and cement paste have been completely removed from the surface of this smooth face block.
Efflorescense occurs in both brick and masonry walls when salts in the masonry wall assembly leach to the surface. Water can enter the wall system in several ways, and later, as the wall dries, the salt solution migrates to the surface. Some clay products contain sulfate compounds. Calcium sulfate can be present in the raw materials; potassium or sodium sulfate can be formed during the brick firing process.
Efflorescence in concrete block occurs from the hydration of cement in the curing process and inevitably produces some calcium hydroxide. When dissolved in water and then brought to the surface in the drying process, calcium hydroxide reacts with carbon dioxide in the air to form calcium carbonate. Efflorescence is most troublesome when weather turns cool with some warmth during the day and cold nights. This affects the rate of evaporation and is known as "new building bloom". The efflorescence in this picture is normal and will be removed during the cleaning process.
High pressure spray cleaning removed the cement paste surrounding the aggregates in this splitface wall. When cement paste containing the pigment is blown away by high pressure cleaning, it leaves only the natural color of the remaining aggregates to provide color of the wall. In this example, the aggregates were gray and the pigment that was removed was earth tone.
This wall shows a combination of cleaning problems. Chemical damage, higher than recommended dilution of cleaning solution, and concentrated high pressure spray cleaning resulted in chemical burning, over-exposure of aggregates and removal of surrounding pigments normally found in the cement paste.
Even from a distance, this building shows streaking from high-pressure spray damage.
Things to consider when cleaning Masonry walls:
Always do a test patch first. Test patches should be approximately a 20-foot square on an inconspicuous part of the structure. Look for chemical burning (discoloration) and exposed aggregates ( pressure too high if using a pressure sprayer), and hazing (chemical solution not rinsed completely) before proceeding to clean the building.
Never clean integrally colored masonry walls or colored mortar with muriatic acid solution. Use a recommended masonry cleaner, being careful not to exceed recommended dilution rate. It is recommended that a test panel be cleaned at different dosage rates to determine best brightness without burning the wall.
Never apply cleaning solution to a dry wall. Cleaning solution should be applied evenly to a fully wet wall, allowed to sit for 2-3 minutes and the work area should then be thoroughly flushed with water to remove all residual cleaning solution. Repeat as needed. Walls should be cleaned from the bottom up so that fresh water flushing continues to remove the cleaning solution. Apply cleaning solution with a hand -pump concrete sprayer for even application. It is not a good idea to apply the cleaning solution with a high-pressure sprayer because the cleaning chemical is forced into the masonry unit capillaries and softens the cement paste that holds the aggregates on the surface.
Never use high pressure spray cleaning. Our recommendation is to not allow the use of a high-pressure sprayer to clean colored masonry walls. If you must use a pressure sprayer, use a fan spray tip at a 45-degree angle with water pressure not to exceed 150 PSI. High-pressure water will actually cause increased efflorescence problems if water is forced into the masonry unit, as it will cause additional soluble salts to migrate to the surface when drying.
Plan your job. Remember that any water entering the wall has to evaporate, bringing soluble salts to the surface. Sources of water entering the wall must be stopped and wall must have completed the drying process before cleaning can begin. A good rule to follow would be to clean the wall between 7-14 days after construction of the wall begins. Removing mortar splatter is easier when the mortar is still green. Clean the wall as you go and cover your work below to minimize cleaning time later. Different type mortars will pose different cleaning challenges. Type "S" mortar will get harder, faster than type "N".
Always start cleaning with the gentlest method possible. To minimize the effects of cleaning on a wall, always start with the gentlest cleaning method possible and progress towards harsher methods as needed. Improper cleaning of masonry surfaces can significantly change a walls color, eat away cementitious material, leave aggregate exposed, and cause additional efflorescence to occur. Remember, once the wall is damaged, there is no going back.
Tools: Below is a picture of tools you should have available for the cleaning process.
