SYSTEMS/PRECAST
The face seal approach employs a single line of defense against rain penetration and air leakage by
employing a field-installed elastomeric joint sealant (see section Design/Sealants). A simple one-
stage joint is shown in Figure 4.4.2. This is the lowest initial cost option and can perform well for
several years, given good joint design, good sealant materials, and careful installation. However,
the sealant is fully exposed to the degrading effects of sunlight, ultraviolet radiation, water and
temperature cycling, increasing the material requirements on the sealant. Over time the
performance of these sealants will decrease, increasing maintenance costs. Also, any defect in the
sealant, even a small gap, will lead to water and air leakage.
SECTION
PLAN
Air and
water seals
Figure 4.4.2 Precast Concrete Panel - One-Stage Joints (Rousseau)
Two-stage joints employ an outer seal to control water leakage and an inner seal for airtightness, as
shown in Figure 4.4.3. Any rainwater that does penetrate the rain barrier drains to the outside well
before it is able to reach the air seal. The inner air seal is now in a less severe environment, being
protected from water and ultraviolet radiation, placing less severe requirements on the sealant
material.
PLAN
SECTION
Air seal
ir seal
Water
Figure 4.4.3 Precast Concrete Panel - Two-Stage Joints (Rousseau)
PAGE 4.4-3
Previous Page
