In two-stage designs, the outer seal sheds most water, and any that passes it drains out through the cavity behind, while the inner seal stops air and the pressure difference that drives water inward. Precast panels, curtain wall and rainscreen cladding use it because a single sealant line has no backup. The cavity must be vented and drained to work.
Precast is a two-stage joint, so if you seal over the weep tubes at the outer bead, the cavity can't drain.
Also heard as
- dual-seal joint
- double seal
- two-stage seal
Related terms
Rainscreen
A wall design with cladding held off the WRB by a vented, drained gap so water can escape and the wall can dry.
Weep
An opening at the base of a wall or window system that lets collected water drain out.
Precompressed foam
Impregnated open-cell foam supplied squeezed flat that slowly expands to fill and seal a joint.
Expansion joint
A designed gap between building elements that lets them move with temperature, settlement and load without cracking.