Deck coatings make excellent choices for remedial situations where it is not possible to allow for the addition of a topping slab or other waterproofing system protection. Deck coatings are installed over concrete, plywood, or metal substrates, but should not beinstalled over lightweight insulating concrete.
Deck coatings are also used to protect concrete surfaces from acid rain, freeze–thaw cycles, and chloride ion penetration, and to protect reinforcing steel.
In certain situations, deck coatings are not specifically installed for their waterproofing characteristics but for protection of concrete against environmental elements. For example,
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 traffic. Aggregate is usually broadcast into the final coat either by hand seeding or by mechanical 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, intermediate, 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 compatible 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:
● Cementitious coatings
● Asphalt overlay
● Modified urethane
● Sheet systems