ASB Trade › Guides › Mounting foam and sealants: which to buy and where to use each
Mounting foam and sealants: which to buy and where to use each
Summer, winter or all-season foam, gun or straw, fire-rated foam, silicone, acrylic or polyurethane sealant: what each is for and how much you will need.
Summer, winter or all-season foam
Mounting foam cures with moisture from the air, so temperature matters. Summer foam works from about +5 °C, winter foam down to about −10…−18 °C, and all-season foam from roughly −10 to +30 °C. The range is printed on the can and refers to the air and surface temperature; the can itself should be warm (about +15…+25 °C), so in winter keep it indoors.
In cold, dry air foam cures more slowly and yields less volume, which is why the gap is sprayed with water first. The standard can is 750 ml; the yield is roughly 40–65 litres depending on the series. One window usually takes one or two cans depending on the width of the gap.
Gun foam or straw foam
Professional foam is made for a gun: it doses precisely, expands less afterwards (so it does not bow the frame) and the can may stay on the gun for several days. You need the gun and a cleaner. Household foam with a straw is a one-off option for a small job, one or two gaps or a hole around a pipe; once opened, the can must be used the same day.
The rules are the same for both: shake the can 20–30 times, dust off and wet the surface, fill the gap to about a third or half of its volume and let the foam expand. Trim the excess after curing (fully after about 24 hours) and always cover it with filler, plaster or paint: in sunlight foam yellows and breaks down.
Fire-rated foam
Fire-rated (fire-retardant) foam contains flame retardants and is usually pink or red so it is visible after installation. It is used in the frames of fire doors, in cable and pipe penetrations between floors and in the walls of plant rooms, wherever the project calls for fire resistance. Ordinary foam is not suitable there: it burns easily. Fire-rated foam is covered the same way as ordinary foam.
Silicone, acrylic or polyurethane
Silicone sealant is elastic and waterproof: bathrooms, kitchens, glazing, plumbing. Acetic silicone smells sharp and bonds well to glass and ceramics, but corrodes metal and stains natural stone; neutral silicone exists for those. Sanitary silicone contains a fungicide and resists mould. Silicone cannot be painted.
Acrylic sealant can be painted and washes off with water: it is for plasterboard joints, skirting boards, window reveals and wall cracks indoors, but it is less elastic and does not tolerate permanently wet spots. Polyurethane sealant is the toughest: strong adhesion to concrete, metal and wood, elasticity and paintability, for facade joints, roofing, concrete joints and outdoor work.
What goes where and how much you need
Window and door installation: foam in the gap, acrylic or polyurethane inside, polyurethane or a dedicated tape outside. Bathtub, shower tray, kitchen worktop: neutral sanitary silicone. Metal roofing, gutters, ridges: polyurethane. Skirting boards and door-frame joints: acrylic, then paint.
Consumption is easy to estimate: a 280–310 ml cartridge covers about 10–12 m of a 5×5 mm joint and about 3 m of a 10×10 mm joint. Smooth the sealant with a spatula or a wet finger and protect the edges of the joint with masking tape. ASB Trade stocks Asmaco, Euromaster and POLUS foams and sealants by the piece or by the box, plus guns and cleaners.
Frequently asked questions
Can summer foam be used in winter?
No; below +5 °C it cures poorly and yields less volume. In winter use winter or all-season foam, keep the can warm and wet the surface.
Which sealant is right for a bathroom?
Sanitary silicone with a fungicide; for acrylic bathtubs and chrome fittings choose a neutral one without the acetic smell. Acrylic sealant is not suitable in a bathroom because it softens in water.
Why does foam have to be covered after curing?
Ultraviolet light breaks foam down: within a few months it yellows and crumbles. Trimmed foam is covered with filler, plaster, tape or paint, and then it lasts for decades.