Construction adhesive vs silicone vs PU foam: which do you need?

Use a construction adhesive when you need to fix one thing to another, such as skirting, panels, trims or a window sill. Use silicone when you need to seal a joint against water and air while letting it move, such as around a shower tray or a window frame. Use PU foam when you need to fill and insulate a gap or cavity, such as the space between a door frame and the wall. Some products overlap, but many failures on site come from asking one of these to do another's job.

The three jobs: fixing, sealing and filling

Fixing: construction and montage adhesives

A construction adhesive is made to carry load. It grabs on contact, holds the piece while it cures, and ends up with real bond strength. It replaces nails, screws and plugs on many interior and exterior fixing jobs. It is not usually made to stay flexible in a moving joint or to look neat as a visible bead.

Sealing: silicone and other sealants

A sealant is made to stay elastic, keep water and air out, and survive the joint opening and closing with heat and movement. Silicone grips well and stays flexible for years, but it is not designed to hold a heavy object up, and it cannot be painted. Our guide on which silicone sealant to use covers acetic, neutral and acrylic grades.

Filling: PU foam

Polyurethane foam expands to fill a cavity, sticks to most building materials and cures rigid, giving thermal and sound insulation. It fills volume cheaply. Once cured it can be cut, sanded and painted, but it is not a finished surface on its own and it is not a substitute for a sealant bead on the outside of a joint.

The adhesives we stock and what each is for

Pattex PL 100: interior, at least one absorbent surface

Pattex PL 100 is a water-based, solvent-free adhesive with the highest initial grab of Henkel's PL range, 180 kg/m². It needs at least one absorbent face to cure, so it is for skirting, architraves, mouldings, ceiling roses, wall panels and insulation board onto plaster, concrete, gypsum board or wood. Henkel gives gap bridging up to 10 mm and asks that heavy items be supported for at least 24 hours. It is interior only and will not cure between two non-absorbent faces.

Pattex PL 150: general purpose, inside and out

Pattex PL 150 is solvent-based, so it works on absorbent and non-absorbent materials alike, including metal and rigid PVC. Henkel publishes it for interior and exterior use, with an initial tack of 100 to 120 kg/m² and gap bridging up to 10 mm. Use it for battens onto blockwork, metal profiles onto masonry and fascia or cladding boards. It is not for constant moisture or for polyethylene, PTFE or acrylic glass, and it needs ventilation.

Pattex PL 200: bonds and seals, including mirrors and wet areas

Pattex PL 200 is a silane-curing polymer that both bonds and seals, cures transparent and can go on glass, mirrors, UPVC and damp surfaces. It bridges gaps up to 20 mm. Henkel's own data shows the trade-off: its final strength (about 3.0 N/mm²) and initial grab (50 kg/m²) are lower than PL 100 and PL 150. You pay for flexibility, a neutral cure and wet-area use, not for raw strength.

Akfix 310: water-based montage adhesive, paintable

Akfix 310 is an acrylic dispersion adhesive for wood, MDF, plaster, polystyrene, stone and tiles. Akfix says one of the surfaces must be porous, the adhesive must be kept away from moisture and rain until cured, and it is not for areas constantly exposed to water. At KSh 500 a cartridge it is an economical choice for interior trims and decorative mouldings.

Akfix MS High Tack: heavy items without clamps

Akfix MS High Tack is a polymer adhesive made to hold heavy building materials without clamps or fixing tape. Akfix lists wall cladding and ceiling panels, insulation and acoustic panels, window sills, doorsteps and skirting, and a long list of substrates including stone, concrete, glass, metals, PVC and wood. It contains no solvent, silicone or isocyanate and can be painted with water-based paint. Akfix says to apply it in vertical strips or dots and bring the parts together within about 10 minutes.

Akfix 610 PU Express: wood in wet areas

Akfix 610 is a fast-curing polyurethane adhesive rated D4 to DIN EN 204, for bonding wood in bathrooms, kitchens and decks and for wood to concrete, metal, stone and foam. Akfix says to clamp or fix the parts for 15 to 20 minutes while it cures. It contains isocyanate, so wear gloves and eye protection.

PU foam

We stock several foams in the PU foam collection, including Akfix 805 in an 850 g can, which Akfix publishes for fixing and insulating door and window frames, filling gaps and cavities, wall penetrations and around pipes and electrical outlets. Akfix also notes that it does not stick to polyethylene, Teflon, silicone or oily surfaces. Our guide on how to use PU foam spray takes you through application step by step.

Decision list by job

• Skirting, architraves, cornices, ceiling roses onto plaster: PL 100 or Akfix 310. Interior, one absorbent face, paintable.
• Timber or metal battens onto blockwork, outside: PL 150 or MS High Tack.
• Heavy wall cladding, stone sills, panels where you cannot clamp: MS High Tack.
• Mirror onto a wall: a neutral mirror adhesive or PL 200. Never acetic silicone. See our guide to fixing a mirror without drilling.
• Wooden worktop, decking or bathroom woodwork: Akfix 610 PU Express.
• Sealing around a bath, basin or shower tray: silicone, not adhesive and not foam.
• Window and door frame gaps: PU foam to fill the cavity, then a silicone or acrylic bead on the face to seal it.
• Gap around a pipe through a wall: PU foam, trimmed and finished.
• Crack in a plastered wall that will be painted: acrylic sealant, not silicone and not foam.
• A bolt or handrail into concrete: none of these. Use a chemical anchor; see our chemical anchor guide.

Mistakes that cost money

• Silicone as a glue. It holds light items, but it is not designed to carry load and it cannot be painted.
• Foam as a fixing. Foam helps hold a frame in position, but frames still need their mechanical fixings.
• Foam left exposed outside. Trim it and cover it with sealant, plaster or paint.
• Water-based adhesive between two non-porous faces. PL 100 and Akfix 310 need one absorbent surface to cure.
• No support while curing. Even high-tack adhesives benefit from a prop or tape on heavy items. Henkel asks for 24 hours' support on heavy items bonded with PL 100.

Buying

All the adhesives above are on our adhesives page. The Pattex PL range is sold by the carton of 12; Akfix cartridges are sold singly and by the box. Contractors and hardware shops can request a carton quote on our trade page. Our Nairobi trade counter is at Royal Business Park, opposite Complast, Old Mombasa Road, Monday to Saturday, 8:00 to 17:30. Delivery is KSh 350 flat countrywide and free over KSh 15,000. Send a photo of the job on WhatsApp if you want help choosing.

Common questions

Can construction adhesive replace screws?

For many interior trims, panels and battens, yes. Henkel publishes PL 150 for mounting jobs you would otherwise drill and plug. For anything overhead, safety-critical or under heavy load, use mechanical fixings, with adhesive as well if you want.

Is PU foam waterproof?

Akfix describes cured 805 foam as waterproof and mould-proof. On the outside of a building, still trim it and seal or plaster over it rather than leaving bare foam as the finished face.

Which adhesive can I paint over?

PL 100, PL 150 (once dry), PL 200, Akfix 310 and MS High Tack (with water-based paint) are all described by their makers as paintable. Silicone is not.

Is there one product that does everything?

PL 200 and MS High Tack come closest, since both bond and can seal. They cost more than a single-purpose product and are not always the strongest choice, so match the product to the main job.