Page 137 - Construction Waterproofing Handbook

3.26 CHAPTER THREE
CEMENTITIOUS COATING APPLICATION

For adequate bonding to substrates, surfaces to receive cementitious coatings should be
cleaned of contaminants including dirt, efflorescence, form-release agents, laitance,
residues of previous coatings, and salts. Previously painted surfaces must be sandblasted
or chemically cleaned to remove all paint film.
Cementitious coating bonding is critical to successful in-place performance. Therefore,
extreme care should be taken in preparing substrates for coating application. Sample appli-
cations for bond strength should be completed if there is any question regarding the accept-
ability of a substrate, especially with remedial waterproofing applications.
Poured-in-place or precast concrete surfaces should be free of all honeycombs, voids,
and fins. All tie holes should be filled before coating application with nonshrink grout
material as recommended by the coating manufacturer. Although concrete does not need
to be cured before cementitious coating application, it should be set beyond the green stage
of curing. This timing occurs within 24 hours after initial concrete placement.
With smooth concrete finishes, such as precast, surfaces may need to be primed with a
bonding agent. In some instances a mild acid etching can be desirable, using a muriatic acid
solution and properly rinsing substrates before the coating application. Some manufacturers
require a further roughing of smooth finishes, such as sandblasting, for adequate bonding.
On masonry surfaces, voids in mortar joints should be filled before coating installation.
With both masonry and concrete substrates, existing cracks should be filled with a dry mix
of cementitious material sponged into cracks. Larger cracks should be sawn out, usually to
3
a 4 in minimum, and packed with nonshrink material as recommended by the coating
manufacturer.
Moving joints must be detailed using sealants designed to perform under the expected
movement. These joints include thermal movement and differential movement joints. The
cementitious material should not be applied over these joints as it will crack and “alliga-
tor” when movement occurs.
If cracks are experiencing active water infiltration, this pressure must be relieved before
coating is applied. Relief holes should be drilled in a substrate, preferably at the base of
the wall, to allow wicking of water, thus relieving pressure in the remainder of work areas
during coating application. After application and proper curing time (approximately 48–72
hours), drainage holes may then be packed with a nonshrink hydraulic cement material and
finished with the cementitious coating.
After substrate preparations are completed and just before application, substrates must be
wetted or dampened with clean water for adequate bonding of the coating. Substrates must be
kept continually damp in preparation for application. The amounts of water used are depen-
dent on weather and substrate conditions. For example in hot, dry weather, substrates require
frequent wettings. Coatings should not be applied in temperatures below 40°F or in conditions
when the temperature is expected to fall below freezing within 24 hours after application.
Cementitious coatings should be carefully mixed following the manufacturer’s recom-
mended guidelines concerning water ratios. Bonding agents should be added as required
with no other additives or extenders, such as sand, used unless specifically approved by the
manufacturer. With smooth surfaces such as precast concrete, an additional bonding agent
is required.