Page 281 - Construction Waterproofing Handbook

5.40 CHAPTER FIVE

FIGURE 5.36 Proper installation of backing material using packer tool. (Courtesy of
SWRI)

Applying bond breaker tape incorrectly can cause joint failure both adhesively and
cohesively. Tape allowed to turn up sides of joints will not allow sealant to adhere properly
to sides, causing adhesion problems. If tape does not completely cover the backs of joints,
three-sided adhesion occurs, causing cohesion failure.
Open-cell materials are usually made of polyurethane; closed-cell materials are manu-
factured from polyethylene. Sealant manufacturers will recommend the appropriate back-
ing to use. Open-cell materials are not recommended for horizontal or submerged joints
where water can collect in open cells. Closed-cell materials are inappropriate for moisture-
cured sealants, since they prohibit air from reaching the back of joint material.
Proper backer rod and tape installation depends on the following:

● Use of an adjustable packing tool to ensure proper depth (Fig. 5.37)
● A backer rod that is 25 percent larger than joint width
● Backing material that corresponds in width to the varying widths of joints
● Horizontal joints without gaps in the rod that would allow sealant to flow through
● Bond breaker tape that covers the entire back of a joint but is not turned up at the sides
● Installation of tape over existing sealant to prevent three-sided adhesion (in remedial
applications, where it is necessary to install new sealant over old)

Mixing, applying, and tooling sealants
Improperly mixed sealants will never completely cure and therefore will never provide the
physical properties required. Improperly mixed sealants are evident from their sticky surface
or softness of material, which can literally be scooped from a joint. All components of a