Silicone sealant | Chalkline

A silicone sealant is a one-part curing sealant based on silicone polymer chemistry, used for perimeter joints in wet areas, glazing, and weatherproofing where a flexible, water-resistant seal is needed against the substrate. It is the volume sealant on residential sites for shower screens, vanity perimeters and exterior window seals. The deeper trade detail is in the silicone sealants material article.

The two cure chemistries

The single most-bungled call on site is picking the wrong cure type:

Neutral-cure silicone. Releases alcohol as it cures. Safe on alkaline substrates (concrete, masonry, stone), copper, brass and bituminous waterproofing membranes. The default for wet-area tile joints, plumbing perimeters and exterior seals.
Acetoxy-cure silicone. Releases acetic acid (vinegar smell) as it cures. Glass and glazing only. Etches concrete, attacks copper and bare metal frames, and corrodes powder-coated aluminium over time.

A vinegar smell out of the gun on a stone vanity or copper flashing is the wrong product on the wrong substrate; back the gun out and re-spec.

Where it sits against the other sealants

For movement joints in masonry, brick or concrete: polyurethane sealant usually outperforms silicone.
For paintable, low-modulus joints on internal trim: MS polymer sealant (silicone cannot be over-painted with most paints).
For old-school putty-style fill: mastic, not silicone.

Where it must NOT be used

Structural glazing or load-bearing joints (use the engineered structural-glazing silicone systems, not a tube product).
Direct contact with bituminous waterproofing membrane when the silicone is acetoxy-cure (membrane attack).
Joints wider than the manufacturer’s stated maximum without a backer rod to control depth-to-width.

Category: Sealants.

The two cure chemistries

Where it sits against the other sealants

Where it must NOT be used

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