Sealants & adhesives: pick the right tube

Sealants and adhesives look similar in the tube but do opposite jobs: a sealant stays flexible and is built to move with a joint (expansion, wind sway), while an adhesive is built to bond and hold. Get this wrong and it bites you — a rigid adhesive where there’s movement will crack, and a soft sealant used as glue will creep.

Sealant or adhesive? Sort that first

Before you worry about brands, decide which job you’re actually doing. After that it comes down to cure chemistry, exposure and substrate — what you’re sticking to and where it lives.

• Sealant — stays flexible, moves with the joint. Use it on movement joints, not as a structural glue.
• Adhesive — built to bond and hold. Don’t rely on it where the joint needs to move.

Polyurethane, silicone & MS polymer

The three workhorse chemistries for flexible bonding and sealing, each with its own strengths.

• Polyurethane (PU) — Sikaflex 11FC is a general-purpose construction adhesive and sealant that bonds and seals; it skins in about 60 minutes, cures in 24–48 hours and is paintable. Sikaflex Pro2 HP is a high-movement structural sealant for cladding joints and glazing perimeters, with higher elongation (over 500%) and UV stability. Bostik Seal’n’Flex 1 is a flexible joint sealant for building movement joints — it skins, is paintable, and works indoor and outdoor.
• Silicone — neutral-cure silicone (a Sikaflex 11FC alternative) suits glazing perimeters, around basins and tubs, and exposed joints; it won’t corrode metal, so use it around copper, brass and galvanised. Acetic-cure silicone (Selleys Allclear) is cheaper and suits glass-to-glass, internal bathrooms and low-budget work, but it smells of vinegar while curing and corrodes metal.
• MS Polymer (modified silyl) — Bostik Fix-All and Sikabond MS give the best of both: high-performance bond and sealant with no isocyanates. Paintable, UV-stable and lower-toxicity than PU, at a premium price.

Construction adhesive, GIB stopping & PU foam

The rest of the shelf: panel adhesives, plasterboard compounds and expanding foam.

• Construction adhesive — Liquid Nails Heavy Duty bonds plasterboard, timber-to-timber and panels, daubed at 600mm centres per GIB fixing instructions. Selleys Trade Liquid Nails is the heavier-duty version, used as a GIB fixing supplement alongside screws.
• GIB stopping compound — GIB Tradeset 45 / 90 / 110 / 180: the number is the setting time in minutes, so Tradeset 45 sets fast for the first coat while Tradeset 180 gives longer working time on big jobs. GIB Plus 4 is a ready-mix all-purpose compound for topcoating over tradeset — no mixing, bucket ready. GIB Cove Adhesive is a quick-setting cornice/cove adhesive that fills the gap behind the cove.
• Polyurethane foam — Sika Boom-200 and Bostik Pro Foam fill gaps around door and window frames and services penetrations; they expand around 30 times, trim flush when cured, and must be covered because they UV-degrade. Fire-rated PU foam (Sika Boom FR) is for fire-rated penetrations through FRR walls, maintaining the FRR up to 240 minutes as a Hilti CP 606 alternative.

Never use acetic-cure silicone near metal

That vinegar smell is acetic acid, and it corrodes copper, brass, galvanised and aluminium as it cures. Never run it near galvanised flashings or copper pipes.

• Near metal — use neutral-cure silicone or MS polymer instead.
• Where acetic-cure is fine — internal glass-to-glass applications away from metal.