Elastomeric
Elastomeric describes a material that cures to a permanently flexible, rubber-like state and recovers with cyclic movement, the property behind PU and silicone sealants.
Ask Chalkline about this →Elastomeric describes a material that cures to a permanently flexible, rubber-like state and can stretch and recover with repeated (cyclic) movement without cracking or losing its seal. It is the key property behind movement-joint sealants and flexible waterproofing membranes: where a joint or substrate moves with thermal expansion, structural load, or settlement, an elastomeric material flexes with it instead of splitting.
The common elastomeric sealants are polyurethane, silicone, and MS polymer, rated to standards such as ASTM C920 for elastomeric joint sealants. Their movement-accommodation factor, how much joint movement they tolerate as a percentage of joint width, is what makes them suitable for a movement joint where a rigid filler would fail. Many liquid-applied waterproofing membranes are elastomeric for the same reason: a wet-area or balcony substrate moves, and a brittle membrane would crack at the junctions.
The opposite is a plastomeric or rigid material (acrylic gap filler, hard grout, cement render) that holds shape but cannot keep recovering through movement cycles; use those for static gaps, not moving joints. Match the sealant’s movement class to the actual joint movement, and detail the joint (backing rod, correct depth-to-width ratio) so the elastomeric bead can stretch as intended rather than tearing at the bond line.
Also known as: Elastomer, flexible sealant, rubber-like sealant.
Category: Materials / Sealants and waterproofing.
Related
See also
References
- ASTM C920 Standard Specification for Elastomeric Joint Sealants (verified 2026-05-11)
- AS 4654.1/.2 Waterproofing membranes for external above-ground use, Standards Australia (verified 2026-05-11)
Last updated: 2026-05-30. Verified: 2026-05-11. Quarterly review for currency.