Page 273 - Construction Waterproofing Handbook

5.32 CHAPTER FIVE
Joint width determines the size of foam material required. If a joint varies considerably,
more than 25 percent in width, different sizes of preformed foam sealant are required in
the one joint.
A horizontal grade is available, allowing use in horizontal plaza and deck joints. Some
have properties sufficient to withstand vehicular traffic as well. Foam sealant adheres to
most clean and prepared building materials, including stone, aluminum, concrete, wood,
and glass.
In addition, foam sealant is compatible with other sealant materials and allows elas-
tomeric sealants to be applied over the foam, providing a double barrier in critical water-
proofing joints. With these applications, foam sealants are acting as a backing material for
elastomeric sealants.
Most foam sealants withstand up to 25 percent movement in either direction, for a total
joint movement capability of 50 percent. Foam sealant performs best in compression mode
with no long-term compression set, returning to its originally installed size.
Critical to successful foam sealant applications are well-cleaned joints. If the joint is
wet or contaminated, the contact adhesive will fail. Materials are usually supplied in black
only, but they can be painted to achieve other coloring, although paints will crack during
movement. (See Table 5.10.)

SUBSTRATES

Successful sealant installation depends upon ensuring that a substrate is compatible with
the material and is in acceptable condition for proper sealant adhesion. Adhesion is essen-
tial, without which all other properties are insignificant.
For example, Teflon®-coated materials, Kynar® finishes, or PVC substrates are espe-
cially difficult to adhere to. Teflon® is manufactured so that other materials do not adhere
to it, thus keeping the surface continually clean. In these cases, butyl rubber sealant might
be chosen over a silicone for its better adhesion capability, provided that substrate move-
ment is within the butyl’s capability.
Sealant incompatibility with a substrate causes staining or etching of substrates. On the
other hand, some substrates, such as oils, asphalt, and coal tar materials, may cause stain-
ing or sealant deterioration. To prevent these problems or when compatibility is in ques-
tion, actual substrate testing with sealants should be done. This can be completed by
testing under laboratory procedures such as accelerated weathering, or by preparing mock-
up panels with the sealant applied at job sites and allowing sufficient time to determine
success or failure.

TABLE 5.10 Precompressed Foam Sealant Properties

Advantages Disadvantages
No priming or backing No colors available
Factory-manufactured Heat and cold affect installation
Nonlabor-intensive Difficult installation for varying joint widths