Building Design and Construction Handbook - Merritt - Ventech!

PROTECTION AGAINST HAZARDS 3.27
Colorless Coating Materials. The colorless ‘‘waterproofings’’ are often claimed
to stop leakage of wind-driven rain through permeable masonry walls. Solutions of
oils, paraffin wax, sodium silicate, chlorinated rubber, silicone resins, and salts of
fatty acids have been applied to highly permeable test walls and have been tested
at the National Institute of Standards and Technology under exposure conditions
simulating a wind-driven rain. Most of these solutions contained not more than
10% of solid matter. These treatments reduced the rate of leakage but did not stop
all leakage through the walls. The test data show that colorless coating materials
applied to permeable walls of brick or concrete masonry may not provide adequate
protection against leakage of wind-driven rain.
Solutions containing oils and waxes tended to seal the pores exposed in the faces
of the mortar joints and masonry units, thereby acting more or less as vapor barriers,
but did not seal the larger openings, particularly those in the joints.
Silicone water-repellent solutions greatly reduced leakage through the walls as
long as the treated wall faces remained water-repellent. After an exposure period
of 2 or 3 hr, the rate of leakage gradually increased as the water repellency of the
wall face diminished.
Coatings of the water-repellent, breather type, such as silicone and ‘‘soap’’
solutions, may be of value in reducing absorption of moisture into the wall surface.
They may be of special benefit in reducing the soiling and disfiguration of stucco
facings and light-colored masonry surfaces. They may be applied to precastconcrete
panels to reduce volume changes that may otherwise result from changes
in moisture content of the concretes. However, it should be noted that a waterrepellent
treatment applied to the surface may cause water, trapped in the masonry,
to evaporate beneath the surface instead of at the surface. If the masonry is not
water-resistant and contains a considerable amount of soluble salts, as evidenced
by efflorescence, application of a water repellent may cause salts to be deposited
beneath the surface, thereby causing spalling of the masonry. The water repellents
therefore should be applied only to walls having water-resistant joints. Furthermore,
application of a colorless material makes the treated face of the masonry waterrepellent
and may prevent the proper bonding of a cementitious coating that could
otherwise be used to stop leakage.
Cementitious Coatings. Coatings of portland-cement paints, grouts, and stuccos
and of pneumatically applied mortars are highly water-resistant. They are preferred
above all other types of surface coatings for use as water-resistant base coatings on
above-grade concrete masonry. They may also be applied to the exposed faces of
brick masonry walls that have not been built to be water-resistant.
The cementitious coatings absorb moisture and are of the breather type, permitting
passage of water vapor. Addition of water repellents to these coatings does
not greatly affect their water resistance but does reduce the soiling of the surface
from the absorption of dirt-laden water. If more than one coating is applied, as in
a two-coat paint or stucco facing job, the repellent is preferably added only to the
finish coat, thus avoiding the difficulty of bonding a cementitious coating to a waterrepellent
surface.
The technique used in applying the cementitious coatings is highly important.
The backing should be thoroughly dampened. Paints and grouts should be scrubbed
into place with stiff fiber brushes and the coatings should be properly cured by
wetting. Properly applied, the grouts are highly durable; some grout coatings applied
to concrete masonry test walls were found to be as water-resistant after 10
years out-of-doors exposure as when first applied to the walls.
Pigmented Organic Coatings. These include textured coatings, mastic coatings,
conventional paints, and aqueous dispersions. The thick-textured and mastic coatings
are usually spray-applied but may be applied by trowel. Conventional paints