Page 134 - Construction Waterproofing Handbook

ABOVE-GRADE WATERPROOFING 3.23
Cementitious coatings are highly resistant to accelerated weathering, as well as being
salt-resistant. However, acid rain (sulfate contamination) will deteriorate cementitious
coatings as it does other masonry products.
Cementitious coatings are breathable, allowing transmission of negative water vapor.
This avoids the need for completing drying of substrates before application, and the spalling
that is caused by entrapped moisture. These products are suitable for the exterior of planters,
undersides of balconies, and walkways, where negative vapor transmission is likely to
occur. Cementitious coatings are also widely used on bridges and roads, to protect exposed
concrete from road salts, which can damage reinforcing steel by chloride attack.

Cementitious installations
Water entering masonry substrates causes brick to swell, which applies pressure to adja-
cent mortar joints. The cycle of swelling when wet, and relaxing when dry, causes mortar
joint deterioration. Cementitious coating application prevents water infiltration and the
resulting deterioration. However, coatings alter the original facade aesthetics, and a build-
ing owner or architect may deem them not acceptable.
Cementitious coatings are only used on masonry or concrete substrates, unlike elas-
tomeric coatings that are also used on wood and metal substrates. Cementitious coating use
includes applications to poured-in-place concrete, precast concrete, concrete block units,
brick, stucco, and cement plaster substrates (Fig. 3.8). Once applied, cementitious coatings
bond so well to a substrate that they are considered an integral part of the substrate rather
than a film protection such as an elastomeric coating.
Typical applications besides above-grade walls include swimming pools, tunnels, retention
ponds, and planters (Fig. 3.9). With Environmental Protection Agency (EPA) approval, these
products may be used in water reservoirs and water treatment plants. Cementitious coatings
are often used for finishing concrete, while at the same time providing a uniform substrate
coloring.
An advantage with brick or block wall applications is that these substrates do not nec-
essarily have to be tuck-pointed before cementitious coating application. Cementitious
coatings will fill the voids, fissures, and honeycombs of concrete and masonry surfaces,
effectively waterproofing a substrate (Fig. 3.10).
When conditions require, complete coverage of the substrate by a process called bag,
or face, grouting of the masonry is used as an alternative. In this process, a cementitious
coating is brush applied to the entire masonry wall. At an appropriate time, the cementi-
tious coating is removed with brushes or burlap bags, again revealing the brick and mor-
tar joints. The only coating material left is that in the voids and fissures of masonry units
and mortar joints. Although costly, this is an extremely effective means of waterproofing
a substrate, more effective only than tuck-pointing.
Complete cementitious applications provide a highly impermeable surface and are used
to repair masonry walls that have been sandblasted to remove existing coatings and walls
that are severely deteriorated. Cementitious applications effectively preserve a facade while
making it watertight. Bag grouting application adds only a uniformity to substrate color;
colored cementitious products can impart a different color to existing walls if desired. Mask
grouting is similar to bag grouting. With mask grouting applications, existing masonry units
are carefully taped over, exposing only mortar joints. The coating material is brush-applied