Page 271 - Construction Waterproofing Handbook

5.30 CHAPTER FIVE
vertical expansion joints. Some urethanes are manufactured to meet USDA requirements
for use in food-processing plants. As with polysulfides, polyurethanes are available in a
wide range of colors. Two-component mixes add coloring to the activator portion that is
mixed with base material.
Polyurethanes are available for a wide range of applications, including precast concrete
panels, expansion and control joints, horizontal joints, flashing, and coping joints. Urethane
sealants are not recommended for continual immersion situations.
Urethane has excellent adhesion to most substrates, including limestone and granite. In
most cases, a primer is not required. However, manufacturer’s data should be reviewed for
uses requiring primers. These include horizontal joints, metals, and extremely smooth sub-
strates such as marble.
Two-component urethanes are low-modulus sealants and have high joint movement
capability averaging 25 percent, with joint design limitation of four times the expected
movement. Since urethanes exceed the movement capabilities of paint, they should not be
painted over because alligatoring of the paint surface will occur. Coloring should be
achieved by using standard manufacturer colors.
Urethanes have excellent recovery capability, 90 percent or more, and possess excellent
weathering and aging characteristics. Since urethanes are extremely moisture-sensitive
during curing, a closed-cell backer rod should be used. However, with one-component ure-
thane sealants an open-cell backing material is acceptable.
Polyurethanes cannot be used in joints containing a polysulfide sealant or residue.
These joints must be cleaned by grinding or other mechanical means to remove any trace
of sulfides. Urethane sealants also should not be used in glazing applications of high-
performance glass, plastics, or acrylics. Joints contaminated with asphalts, tar, or form-
release agents must be cleaned before sealing work.
Polyurethane’s compatibility with most substrates, excellent movement and recovery
capability, and good weathering characteristics have allowed their widespread use in
waterproofing applications both above and below grade. Their ability to withstand vehic-
ular traffic and compatibility with urethane deck coatings leads to their extensive use in
parking deck applications. (See Table 5.8.)

Silicones
Silicone sealants are derivatives of silicone polymers produced by combining silicon, oxy-
gen, and organic materials. Silicones have extremely high thermal stability and are used as
abrasives, lubricants, paints, coatings, and synthetic rubbers. Silicones are available in a
wide range of compositions that are extremely effective in high-movement joints, includ-
ing precast panels and expansion joints. When used properly, silicone sealants provide

TABLE 5.8 Polyurethane Sealant Properties

Advantages Disadvantages
Good elongation capability Moisture sensitive
Excellent recovery rates Unpaintable
Horizontal applications Require some priming