Page 272 - Construction Waterproofing Handbook

SEALANTS 5.31
excellent movement capability, as much as 50 percent, and adhesion and recovery proper-
ties after movement.
Silicone sealants cannot be used for below-grade applications, horizontal applications
subject to vehicular traffic, and water immersion joints. It is extremely important not to
install silicone materials over materials that might bleed through a silicone. This includes
oil, solvents, or plasticizers, which will cause staining and possible silicone failure.
Uncured silicone must not encounter nonabradable substrates such as metal, polished
granite, or marble. The uncured sealant can leave a residue that stains or changes the sub-
strate appearance. This is also true for primers used with silicone sealants. Masking adja-
cent surfaces is necessary to protect against damage.
Silicones contaminate all surfaces or substrates they encounter. This makes it virtually
impossible to seal over silicone residue with other materials such as urethanes. Abrasive
methods are the only acceptable methods for removing silicone from a substrate before
resealing it with another product. Most substrates do not require primers for silicone appli-
cations; however, natural stone materials such as limestone and marble will require primers.
Most silicone is produced in one-component packaging, although two-component prod-
ucts are available. Silicones have excellent adhesion to almost all building products includ-
ing wood, ceramic, aluminum, and natural stones. Silicones may be used in curtain wall
joints, precast panels of concrete, marble, or limestone, and expansion and control joints.
Silicone materials exceed the movement capability of paints, and as most paints will not
adhere to silicones, they should not be painted over. Most silicones are now produced in a
wide range of colors; in addition, special color blending is available by the manufacturer.
Both open-cell and closed-cell backing materials can be used with silicone joints.
Silicones have excellent recovery capabilities, usually up to 100 percent. They have
very little initial cure shrinkage, 3 percent, and a tackfree time of only 1–3 hours. High-
tensile-strength silicones with lower movement capabilities are typically used in glazing
applications. (See Table 5.9.)

Precompressed foam sealant
Foam sealants are manufactured by impregnating open-cell polyurethane foam with chem-
ical sealant containing neoprene rubbers. An adhesive is applied to one side and covered
with a release paper. The foam is then compressed and supplied in rolls with various
widths of up to 12 in.
Foam sealants are applied by unrolling the foam, removing release paper exposing the
adhesive, and installing into a joint. The foam then swells and expands to fit tightly against
both joint sides, allowing for any irregularities in joint width. Splices in material are pre-
pared by overlapping or butting joint ends. This material eliminates the need for joint back-
ing, primers, and tooling.

TABLE 5.9 Silicone Sealant Properties
Advantages Disadvantages
High-movement capability No submersion applications
Excellent adhesion Possible staining
Excellent recovery rates No below-grade uses