Masonry Magazine May 1972 Page. 16
or other stain producing items attached to the wall should be insulated from the visible portion of the wall by a non-staining durable gasket material having a drip to divert potential staining material away from the wall.
Some manufacturers of customized masonry units have found it advisable to recommend coating the wall with one of the transparent water repellant coatings; the purpose of the coating would not be to waterproof the building, but rather to maintain a clean appearance. The transparent coating, while tending to shed water, would also prevent
small dirt and soot particles from entering the surface and contributing to a stained appearance.
Surface treatments which clean the wall as well as creating subtle changes in its appearance include sand blasting and acid washing. Sand blasting will tend to round off aggregate particles at the surface thereby creating a satiny sheen when light strikes the surface of the wall. Acid wash, although not generally recommended for concrete, can be effectively employed with customized concrete masonry. A weak acid wash removes laitance from the surface and leaves exposed
aggregate particles sharp and angular. When light strikes the wall that has received an acid wash, the wall appears to have much depth of color, sparkle, and life. A stronger acid wash yields a darker background or aggregate color. The "weak" acid for use with concrete masonry would consist of 1 part of muriatic acid to from 6 to 10 parts of water. The "strong" acid would consist of one part of muriatic acid to 3 parts of water. Of course, the wall surface should be wetted down prior to the application of acid and thoroughly rinsed afterwards.
NATIONAL CONCRETE MASONRY ASSOCIATION
P.O. Box 9185, Rosslyn Station, Arlington, Virginia 22209