Masonry Magazine February 1988 Page. 19
NCMA-TEK
45
An Information series from National Concrete Masonry Association
ASSOCIATION
Removal of Stains from Concrete Masonry Walls
General
The past decade has seen a tremendous increase in the use of exposed, unpainted concrete masonry walls. The availability of attractive masonry units-split block, fluted block, sculptured block, etc. - at relatively low cost enables concrete masonry to be used as the facing material for all types of buildings, including residential, commercial, and monumental. Where concrete masonry is used as the facing material without a paint covering, greater attention to workmanship, construction details and consistency of units and mortar is necessary.
Cleaning and Stain Removal
During construction, particular care need be taken to prevent mortar smears on the face of the block. Mortar droppings which adhere to the exposed face of a unit can be removed with a chisel after being allowed to dry and harden. The remaining mortar can then be removed with a stiff fiber brush.
Cleaning of unpainted walls can usually be done by scrubbing with water and a small amount of detergent. Clay or dirt should first be removed with a dry brush. Some efflorescence can be removed when it first appears by simple hosing with water but most efflorescence requires brushing with acid. One part muriatic acid and nine parts water is a good concentration adequate for the job and not too disagreeable to work with. Care must be taken to prevent splashing on floors and other surroundings. The wall must be rinsed thoroughly afterward with a hose if outdoors, or several times with buckets of clean water and sponges if indoors. Rubber gloves and goggles should be worn. Since the acid wash will probably create a subtle change in the appearance of the surface with which it comes in contact, care must be taken to wash the entire wall to avoid undesirable variations in appearance.
Maintenance of the well designed and constructed masonry wall is minimal. On unpainted masonry surfaces, however, inadvertent staining from oil, grease or other foreign substances can destroy the appearance of an otherwise attractive structure. Stains resulting from metal or other attachments to the wall can also create appearance problems. Tables 1 and 2 provide information covering removal of many common staining materials. Table 1 describes the chemicals, detergent, or poultice materials recommended for particular stains and contains letter keys pertaining to the sequence of steps which should be followed in removing the stain. Table 2, Procedure for Stain Removal, includes the identification letters and the particular procedure associated with the letter for cross-reference with Table 1.
TEK 45 © 1972 National Concrete Masonry Association