Cleaning Problems - Causes & Remedies

Cleaning Problems - Causes & Remedies

The cleaning of masonry is not normally a problem. However, when it is performed improperly, the remedy can be costly. Improper cleaning can result in one of the following two problems: stains; i.e. primarily light green, brown, or white, or loss of surface sand coating.

Stains

Most brickwork is hard to stain, particularly brick that has a red body color. Staining will occur more frequently in light body brick or in any body brick when manganese or additives have been added to the body mix. Rarely will brick stain without the presence of an acid. Checking a cube of unused brick away from the building should confirm if the staining occurred before or after installation. Frequently, the job superintendent will watch the brick being cleaned and believe that cleaning instructions are being followed precisely. Without fully understanding what can go wrong, the cleaner may have stained the brickwork.

The larger the mortar smears and the longer the mortar has been on the wall, the more difficult the cleaning. Consequently either stronger cleaners or more rubbing is necessary to clean the brick. Most cleaners contain hydrochloric acid (HCl), i.e. muriatic acid. Commercial cleaners all contain HCl, however some products contain special additives to make the cleaners work more effectively with sensitive brick.

So, what can go wrong to cause staining? Under normal cleaning procedures, as outlined in Hanson Brick Technical Profile #1A, the wall to be cleaned should be thoroughly wetted before the chemicals are applied to ensure acid is not absorbed into the brick. The cleaner should then be applied and allowed to sit on the brickwork for 3 to 6 minutes to soften the mortar and a bristle brush should be used to scrub the mortar from the brick face. The mortar and cleaner are then to be rinsed off the wall.

However, when improper procedures occur as listed below, cleaning problems will develop.

• Prewetting too large an area, causing part of the wall to dry out before the cleaner is applied.
• Not prewetting the wall below the section being cleaned prior to the chemicals being rinsed off.
• Ignoring hot, dry, windy weather, causing the walls to dry out quickly.
• Using contaminated water.
• Applying too strong a cleaning solution or the incorrect cleaning solution.
• Waiting too long to rinse off the chemicals.
• Not rinsing the walls sufficiently to rinse off all the chemicals.
• Applying the chemicals with high pressure, which will force the acid past the surface water.
• Prewetting under high pressure can break down mortar joints, leading to the chemicals getting deep into the wall.