Page 169 - Construction Waterproofing Handbook

3.58 CHAPTER THREE

FIGURE 3.46 Deck-coating application; note crack detailing.
(Courtesy of Karnak)

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 resis-
tance 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 pen-
1
3
etrate deepest, up to 2 in. Siloxanes penetrate to a depth of approximately 4– 8 in.
1
Urethanes, containing higher solids content, penetrate substrates approximately 8 in.
1
Silicone derivative sealers react with concrete and atmospheric humidity to form a chem-
ical 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