Masonry Magazine October 1994 Page. 23
Cover the Top
Prevent rain from entering walls by covering the tops of walls at the end of each working day. This practice helps reduce the possibility of efflorescence.
Put the Inside Edge Up: Turn the inside scaffold board on edge at the end of each working day to prevent rain from splashing mortar and dirt onto the masonry wall.
Spot-Clean Smears: When practical and compatible with the masonry unit, use a stiff fiber brush and water (with or without sand) to scrub mortar smears off the masonry surface. This is most effective when performed within a day or two of the occurrence of the mortar smear.
Cleaning Procedures
Dry brushing is perhaps the least aggressive cleaning procedure available. It is effective in removing loose dust, sand, and some types of efflorescence from the surface of newly constructed masonry. On small projects or where meticulous care has been taken to limit and remove mortar smears during construction, dry brushing is often adequate.
Dry brushing is often not sufficient on larger projects that entail more demanding cleaning requirements. The use of "bucket-and-brush" cleaning with a cleaning agent may provide the best alternative. The cleaning agent can be water, detergent and water, a dilute acidic solution, or proprietary solutions manufactured specifically for masonry cleaning. Selection of an appropriate cleaning solution requires: consideration of the masonry units, evaluation of the substance(s) intended to be removed from the surface of the masonry, and consideration of building elements and materials next to the masonry. Select the cleaning solution that will provide adequate cleaning without significantly eroding the surface of either the units or mortar. Obviously, if cleaning with water or water and a detergent will satisfactorily remove objectionable substances from the masonry, the use of acidic solutions (including acidic proprietary solutions) should be avoided.
A dilute solution of hydrochloric (muriatic) acid is often used to clean mortar smears from the face of clay masonry construction. Some architectural concrete masonry may be cleaned in the same way. Mix the acid with water in a non-metallic container at a ratio of 1:19 (5% solution) or 1:9 (10% solution). Never add water to concentrated acid. As an alternative, proprietary acid-based masonry cleaning solutions may be used. Such cleaning solutions often incorporate detergents and wetting agents in their formulation. They are usually sold as concentrates and must be carefully mixed with water in accordance with the manufacturer's recommendations. Before using an acid or proprietary cleaning solution, always check with the manufacturer of the masonry units to confirm that the proposed solution will not damage those units.
Careful selection of cleaning agents and techniques is required to remove mortar smears like these (left) without damaging units or mortar (right).
Adjacent building elements and materials that could be etched or stained by the cleaning solution must be protected. In particular, metallic and painted surfaces should be covered with polyethylene or another effective barrier to the cleaning solution.
Thoroughly wet masonry surfaces with clean water before applying a detergent or acid based cleaning solution to the masonry. This presoaking will prevent the cleaning solution from being absorbed deep into the pores of the masonry where it may react with masonry materials resulting in chronic efflorescence or staining. The cleaning solution should be applied liberally with a stiff bristle brush (non metallic) and allowed to stand for approximately five minutes. Start at the top of the Wall and work down. Make sure that masonry below is pre-wet and other surfaces are protected. Work with small sections of the masonry. Scrubbing should be concentrated on removing smears from the face of units, not on the surface of mortar joints. The cleaning solution must be thoroughly rinsed from the masonry with clean water before it starts to dry into the masonry. Failure to adequately wet the masonry prior to application of the cleaning solution and failure to completely rinse the masonry after application of the cleaning solution often result in a "white scum" residue on the surface of the masonry. Compounds dissolved by the cleaning solution when dried into the surface of the masonry may no longer be soluble in a conventional acidic cleaning solution and can be virtually impossible to remove without damaging the masonry.
MASONRY-SEPTEMBER/OCTOBER, 1994 23