MS polymer sealant
MS polymer is a modified silyl polymer sealant: paintable, low-VOC, bonds to most substrates without primer. Hybrid alternative to silicone and polyurethane.
Ask Chalkline about this →An MS polymer sealant (modified silyl polymer, also called hybrid polymer) is a moisture-cured sealant chemistry that combines properties of silicone and polyurethane while avoiding the worst tradeoffs of each. It is paintable (unlike silicone), low-VOC and isocyanate-free (unlike most polyurethanes), and bonds to most building substrates without a primer, including some damp surfaces.
Why builders use it
- Paintable: takes most paint systems, suits internal trim and any joint that will be painted over.
- Primer-free: bonds to concrete, masonry, timber, metal, glass, fibre cement, and most plastics straight from the tube (check TDS for exceptions).
- No isocyanates: WHS-friendlier than polyurethane on enclosed-space jobs.
- UV-stable: holds colour and elasticity outdoors on par with silicone.
Common Australian brands: Fixall (Bostik), UltraSet (Bostik), Sikaflex AT range. See MS polymer sealants (materials) for product comparison and TDS detail.
When silicone or polyurethane is still the call
- Wet-area perimeter seals: neutral-cure silicone rated for AS 3740.
- Heavy structural adhesive: polyurethane construction adhesive out-pulls MS polymer on large bonds.
- High-temperature exposure (chimneys, flues): high-temp silicone holds where MS polymer does not.
Also known as: modified silyl polymer sealant, MS-polymer sealant, hybrid polymer sealant.
Category: Materials / sealants
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Last updated: 2026-05-29. Verified: 2026-05-29. Quarterly review for currency.