DECK-COATING CHARACTERISTICS

Deck coatings bond directly to concrete, wood, or metal substrates. This prevents lateral movement of water beneath the coatings, as is possible with sheet good systems. Once cured, coatings are nonbreathable and blister if negative vapor drive is present. This is the reason deck coatings, with the exception of acrylic and epoxies, are not recommended for slab-on-grade applications. Specifically, moisture in soils is drawn up into a deck by capillary action, causing blistering in applied deck coatings. In the same manner, blistering occurs in deck coatings applied on upper deck portions of sandwich-slab membranes due to entrapped moisture and negative vapor drive. In both cases, an epoxy vapor barrier prime coat should be installed to protect deck-coating systems from being subjected to this vapor drive.

Physical properties of deck coatings vary as widely as the number of systems available. Important considerations to review when choosing a coating system include tensile strength, elongation, chemical resistance, weathering resistance, and adhesion properties. Different installation types, expected wearing, and weathering conditions require different coating types.

High tensile strength is necessary when a coating is subject to heavy wear including vehicular traffic or forklift traffic at loading docks. Tensile strengths of some deck coatings exceed 1000 lb/in^2 (tested according to ASTM D-412) and are higher for epoxy coatings. This high tensile strength reduces the elongation ability of coatings.

Elongation properties range from 200 percent (for high-tensile-strength top coats) to more than 1000 percent (for low-tensile-strength base coats). For pedestrian areas where impact resistance and heavy wear is not expected, softer, higher elongation aromatic ure- thanes are used. Sun decks subject to impact from lawn chairs and tables would be better served by a coating between the extremes of high and low tensile strength.

Chemical resistance can be an important consideration under certain circumstances.
Parking garage decks must have coatings resistant to road salts, oil, and gasoline. A pedes- trian sun deck may be subjected to chlorine and other pool chemicals. Testing for chemical resistance should be completed according to recognized tests such as ASTM D-471.

Weathering resistance and ultraviolet resistance are important to coatings exposed to the elements such as on upper levels of a parking garage. These areas should be protected by the ultraviolet-resistant properties of coatings such as an aliphatic urethane. Weathering characteristics can be compared with accelerated weathering tests such as ASTM D-822.

Other properties to consider on an as-needed basis include adhesion tests, solvent odor for interior uses, moisture vapor transmission, and fire resistance.

Once installed, the useful life of deck coatings depends upon proper maintenance as well as traffic wear. Heavily traveled parking garage decks and loading docks will wear faster than a seldom-used pedestrian deck area. To compensate, manufacturers recommend a minimum of one to as many as three additional intermediate coat applications. Additional aggregate is also added for greater wear resistance (Fig. 3.20).

FIGURE 3.20 Suggested aggregate texture layout for
maximum protection of deck coating.

With proper installation, deck coatings should function for upward of 5 years before requiring resealing. Resealing entails cleaning, patching existing coatings as required, reapplying top coatings, and, if required, adding intermediate coats at traffic lanes. Proper maintenance prevents coatings from being worn and exposing base coatings that cannot withstand traffic or exposure.

Exposed and unmaintained deck-coating systems require complete removal and replacement when repairs become necessary. Chemical spills, tears or ruptures, and improper usage must also be repaired to prevent unnecessary coating damage. Maintaining the top coat or wearing surface properly will extend the life cycle of a deck-coating system indefinitely.

Deck coatings are also effective in remedial waterproofing applications. If a sandwich- slab membrane installed during original construction becomes ineffective, a deck coating can be installed over the topping slab provided proper preparatory work is completed.

Deck coatings can also be successfully installed over quarry and other hard-finish tile sur- faces, precast concrete pavers, and stonework. With any special surfacing installation, proper adhesive tests and sample applications should be completed.