Page 304 - Construction Waterproofing Handbook

6.8 CHAPTER SIX
The two installation methods for T-joints are fluid-applied and preformed. Both use
sealant materials, but a preformed system uses a sealant that has been formed and precured
(see Fig. 6.5). This cured material is then placed into a joint at the job site. Fluid-applied
systems are placed directly into a joint at sites after mixing and before curing (see Fig. 6.6).
Both systems have distinct advantages and disadvantages.
Preformed systems allow for uniform sealant thickness and curing under controlled
conditions. This prevents possible abuse that may occur during curing of fluid-applied sys-
tems. Preformed systems are not seamless applications and require a site filling of seams
with compatible sealant.
Preformed material is usually formed in 8 ft lengths, requiring seams every 8 ft.
Preformed systems do not make allowances for irregularities with levelness of a substrate.
The nosing is applied after the preformed sealant placement, to alleviate any irregularities
in joint width and levelness.
Fluid systems are vulnerable to damage and weathering during the curing stage. Colder
temperatures may extend the length of typical curing time from 48 to 72 hours. Sealants used
in expansion joints are typically a self-leveling grade. This causes fluid-applied sealants to
flow to low ends of a joint, resulting in uneven joint thickness. Fluid systems may shrink
somewhat in the long joint, and possibly pull away from the nosing during curing.
Bond breaker tape is required between a concrete deck and a reinforcement plate and
between this plate and sealant. If bond breaker tape is installed improperly and turns up
joint sides, improper adhesion will occur. Refer to Chap. 5 for further discussion of sealant
tape installation.

FIGURE 6.5 Sealing preformed T-joint seams. (Courtesy of Coastal Construction Products)