When the sealant and its bond are stronger than the surface, the surface gives instead: weak concrete skin, poorly bonded paint, EIFS base coat or crumbling mortar tears off with the bead. It means the sealant modulus is too high for the substrate or the surface was weak to begin with. Low-modulus sealants and removing weak surface layers fix it.
Bead came off with a layer of paint on the back, that's substrate failure, the coating's the weak link.
Also heard as
- substrate cohesive failure
Related terms
Modulus
How stiff a cured sealant is, meaning how much force it pulls on its bond faces when stretched.
Laitance
A weak, powdery skin of cement and fines on the surface of concrete that sealants and membranes cannot hold onto.
Adhesive failure
A sealant pulling cleanly away from one joint face, leaving the substrate bare.
Spalling
Concrete, brick or stone breaking off in flakes or chunks at the surface.