Page 306 - Construction Waterproofing Handbook

6.10 CHAPTER SIX

FIGURE 6.7 Foam expansion-joint detailing.

Expanding foam sealant
Foam sealants should not be confused with generic sealants. Expanding foam sealants are
composed of open-cell polyurethane foam, fully impregnated with a manufacturer’s pro-
prietary product formulation; these include neoprene rubbers, modified asphalts, and
acrylic materials. Foam sealants are covered in detail in Chap. 5. A typical foam expansion
joint is detailed in Fig. 6.7.
Foam materials are supplied in a compressed state, in rolls of various widths and
lengths. For large widths, straight pieces 8–10 ft long are manufactured. A release paper
over the adhesive on foam sealant facilitates installation.
These materials have considerably fewer elongation properties than better sealants,
(150 versus 500 percent for sealants). They also have lower tensile strengths than
2
sealants (20 versus 200 lb/in ).
With limited elongation properties, these joints should be designed to be in a continuous
compression rather than an elongation mode. Therefore, materials are provided in widths of
two to five times the actual joint width, allowing materials to be in compression always.
Foam systems are particularly easy to install. The material is completely premanufac-
tured and requires only that the joint be cleaned, contact paper removed, and the materials
adhered to one side of the joint. Foam sealants then expand to fill a joint completely. Timing
of this expansion is dependent on weather conditions, being slower in colder weather. These
materials expand laterally and will not expand vertically out of a joint if properly installed.
Foam materials are extremely durable considering their low tensile strength. Once
installed, foam is difficult to remove and is resistant to traffic and vandalism. Depending
on the impregnating chemicals used, they can also be resistant to gasoline and oils.
Manufacturers produce several grades and compositions of materials designed for spe-
cific types of installations. These include below-grade and above-grade joints, vertical or
horizontal applications, and high-traffic grade for bridges and highways.
For vertical expansion joints, foam is often used as backup for a fluid-applied sealant.
Horizontal installations do not require a cover plate or other protection. Foam sealants are
also used as secondary protection in T-joints and are installed in place of standard backing
material in a joint beneath the support plate.