Cohesive failure in service often points to joints that are too narrow for the movement, three-sided adhesion, sealant that is too thick, weathering or reversion. In a pull test, though, cohesive tearing is the desired result, because it proves adhesion is stronger than the sealant. Inspectors note whether a split runs down the center of the bead or near a face.
Bead split right down the middle, cohesive failure, the joint's moving more than that sealant's class.
Also heard as
- cohesive tear
- cohesive split
Do not mix it up with
- Adhesive failure: Adhesive failure is the sealant peeling off the joint face, a surface prep or primer problem.
Related terms
Adhesive failure
A sealant pulling cleanly away from one joint face, leaving the substrate bare.
Three-sided adhesion
Sealant bonded to both joint faces and the back of the joint, which locks it in place so it tears when the joint moves.
Field adhesion test
A test that cuts a tab of cured sealant from an installed joint and pulls it to see whether it lets go of the substrate.
Movement capability
How far a sealant can stretch and compress, as a percentage of joint width, while keeping its seal.