Page 256 - Construction Waterproofing Handbook

SEALANTS 5.15

FIGURE 5.17 Water infiltration through pervious surfaces can
bypass primary joint seals.

FIGURE 5.18 Exterior sealing of double joint. (Courtesy of
Dow Corning)

primary barrier itself, preventing water infiltration directly through the joint if the sealant
material fails in any manner.
Unlike double sealing, the secondary seal is adjacent to the sealant material and often
is used in lieu of backer materials (Fig. 5.20). Figure 5.21 details the difference between
secondary seal and doubled-seal joints. The secondary seal should be manufactured to pre-
vent adhesion to the sealant (Fig. 5.22), eliminating three-sided adhesion when the backer
material is deleted. Secondary seals can also be used beneath the backer materials, as
shown in Fig. 5.23.