Clear wall sealers differ from elastomeric coatings in much the same way that clear deck sealers differ from deck coatings. Clear deck sealers cannot bridge cracks in a substrate, whereas most deck coatings bridge minimum cracking. Clear sealers can be applied only over concrete substrates, whereas deck coatings can be applied over metal and wood substrates. Clear sealers are penetrating systems, whereas deck coatings are surface sealers.
Unlike clear sealers for vertical applications, the chemical composition of horizontal deck sealers is limited. It includes silicone derivatives of siloxanes and silanes and clear urethane derivatives. The majority of products are siloxane-based.
A sodium silicate type of penetrating sealer is available. This material reacts with the free calcium salts in concrete, bonding chemically to form a dense surface. The product is typically used as a floor hardener, not as a sealer. Sodium silicates do not have properties that sufficiently repel water and the chlorides necessary for protecting concrete exposed to weathering and wear.
To ensure sealer effectiveness to repel water, test results such as ASTM C-642, C-67, or C-140 should be reviewed. Reduction of water absorption after treatment should be over 90 percent and preferably over 95 percent. Additionally, most sealers are tested for resistance to chlorides to protect reinforcing steel and structural integrity of concrete. Tests for chloride absorption include AASHTO 259 and NCHRP 244. Effective sealers will result in reductions of 90 percent or greater.
Penetration depth is an important consideration for effective repellency and concrete substrate protection. As with vertical sealers, silanes with smaller molecular structure penetrate deepest, up to 1 /2 in. Siloxanes penetrate to a depth of approximately 1/ 4 – 3/ 8 in.
Urethanes, containing higher solids content, penetrate substrates approximately 1/ 8 in.
Silicone derivative sealers react with concrete and atmospheric humidity to form a chemical reaction bonding the material to a substrate. This provides the required water repellency.
Substrates can be slightly damp but not saturated for effective sealer penetration. Over dense, finished concrete, such as steel-troweled surfaces, acid etching may be required.
Since sealers are not completely effective against water-head pressures and do not bridge cracks, proper detailing for crack control, thermal and differential movement, and detailing into other envelope components must be completed. Expansion joints, flashings, and counterflashings should be installed to provide a watertight transition between various building envelope components and deck sealers.
Clear deck sealers are often chosen for application on balconies and walkways above grade (not over occupied spaces) as well as for parking garage decks. In the latter, the upper deck or lower decks, which cover occupied areas, are sealed with deck coatings, while intermediate decks are sealed with clear sealers. (See Table 3.22.)