Page 148 - Construction Waterproofing Handbook

ABOVE-GRADE WATERPROOFING 3.37
whereas deck coatings on the first floor of a parking garage protect occupied offices on
ground level, they also protect concrete against road salts and freeze–thaw cycles on all
other levels. In these situations, coatings are installed to prevent unnecessary maintenance
costs and structural damage during structure life-cycling.
Deck coatings are usually installed in two- to four-step applications, with the final coat
containing aggregate or grit to provide a nonslip wearing surface for vehicular or foot traf-
fic. Aggregate is usually broadcast into the final coat either by hand seeding or by mechan-
ical spray such as sandblast equipment. Aggregates include silica sand, quartz carbide,
aluminum oxide, or crushed walnut shells. The softer, less harsh silica sand is used for
pedestrian areas; the harder-wearing aggregate is used for vehicular traffic areas. The
amount of aggregate used varies, with more grit concentrated in areas of heavy traffic such
as parking garage entrances or turn lanes.
Due to the manufacturing processes involved, deck coatings are available in several
standard colors but usually not in custom colors. A standard gray color is recommended
for vehicular areas because oils and tire trackings will stain lighter colors. Some manu-
facturers allow their coatings to be color-top-coated with high-quality urethane coatings,
if a special color is necessary, but only in selected cases and not in vehicular areas.
Deck coatings are supplied in two or three different formulations for base, intermedi-
ate, and wearing coats. Base coats are the most elastomeric of all formulations. Since they
are not subject to wear, they do not require the high tensile strength or impact resistance
that wearing layers require. Lower tensile strength allows a coating to be softer and, there-
fore, to have more elastomeric and crack-bridging characteristics than topcoats. As such,
base coats are the waterproof layer of deck-coating systems.
Top and intermediate coats are higher in tensile strength and are impact-resistant to
withstand foot or vehicular traffic. However, the various coating layers must be compati-
ble and sufficiently similar to base coat properties not to crack or alligator as a paint
applied over an elastomeric coating might. This allows base coatings to move sufficiently
to bridge cracks that develop in substrates without cracking topcoats.
Adding grit or aggregate in a coating further limits movement capability of topcoats.
The more aggregate added, the less movement topcoats can withstand, further restricting
movement of base coats.
Deck coatings are available in several different chemical formulations. They are differ-
entiated from clear coatings, which are penetrating sealers, in that they are film-forming
surface sealers. Deck coating formulations include the following:

● Acrylics
● Cementitious coatings
● Epoxy
● Asphalt overlay
● Latex
● Neoprene
● Hypalon
● Urethane