Page 180 - Masonry and Concrete

Masonry Construction Techniques
179
MASONRY CONSTRUCTION TECHNIQUES

effects. New masonry may be cleaned by scrubbing with water, deter-
gent, a muriatic acid solution, or proprietary cleaning compounds.
Detergent solutions will remove mud, dirt, and soil accumulations.
1
One-half cup dry measure of trisodium phosphate and 2 cup dry
measure of laundry detergent dissolved in 1 gal. of water is recom-
mended. Acid cleaners must be carefully selected and controlled to
avoid both injury and damage. Hydrochloric acid (commonly called
muriatic acid) dissolves mortar particles and should be used carefully
in a diluted state. Muriatic acid should be mixed with at least nine
parts clean water in a nonmetallic container, and metal tools or
brushes should not be used. Acid solutions can cause green vanadium
or brown manganese stains on some clay masonry and should not be
used on light colored tan, buff, brown, black, pink, or gray brick which
contains manganese coloring agents. Proprietary cleaning compounds
should be carefully selected for compatibility with the masonry mate-
rial, and the manufacturer’s recommended procedures and dilution
instructions should be followed.
Some contractors use pressurized water or steam cleaning com-
bined with detergents or cleaning compounds. If the wall is not thor-
oughly saturated before beginning, high-pressure application can
drive the cleaning solutions into the masonry, where they may become
the source of future staining problems. High-pressure washing can
also damage soft brick and mortar and accelerate deterioration. Abra-
sive sandblasting should not be used to clean masonry.
All cleaning solutions, even detergent, should be tested for adverse
effects on a small, inconspicuous area of the wall. Some detergents
contain soluble salts that can contribute to efflorescence. Muriatic acid
can leave a white scum on the wall if the residue of dissolved cement
is not thoroughly rinsed after a brief dwell time and light scrubbing.
This white scum can only be removed with special proprietary com-
pounds, or it may have to simply wear off. Detergent and acid solu-
tions usually are applied by bucket and brush, but large jobs may
require low-pressure spray application. The masonry should be thor-
oughly saturated from the top down before cleaning to prevent absorp-
tion of the acid or the dissolved mortar particles. Failure to adequately
prewet a wall, or using an acid solution that is too strong will cause
acid burn—a chemical reaction that changes the color of the masonry.
Nonmetallic buckets, brushes, and tools must always be used with

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