Foam applicator gun



  1. Shake the can, room temperature.
  2. Which way up?
  3. First squeeze on the trigger is best done outside.
  4. Apply a little at a time and allow it to expand.
  5. Use sticks, pins and props.
  6. Don’t change the can inside.
  7. Don’t damage the tip or drop the gun.
  8. Keep it clean.
  9. Keep a can on it.
  10. Lock it off when finished.


Foam applicator gun – expanding foam filler is an invaluable material for sealing up draughts and a versatile adhesive for securing things in place without the need for mechanical fixings such as screws and nails. Foam filler is ideal for preventing air ingress, it is a good insulator, preventing the conduction of heat and also preventing moisture vapour migrating to cold surfaces causing condensation.

Single-use canisters have a disposable plastic nozzle, they are difficult to control and have to be used up completely once opened. A foam gun is a reusable applicator using a different canister design that screws into the gun and allows the canister to be closed off for future use. It has a controllable trigger to moderate the flow, allowing the foam to be applied at the appropriate rate to suit a range of uses.

The applicator gun has five components: nozzle, pin, trigger, lock-off screw and inlet valve.

At the tip of the gun is the nozzle. An optional section of plastic tube can be pushed onto the nozzle allowing the gun to reach deeper into awkward positions. Once used, the tube can be discarded, or flushed with cleaner for reuse.

In the centre of the nozzle is the pin, this opens and closes the nozzle. Be careful not to damage the nozzle or pin, either while poking it about in use or whilst cleaning away old foam. Damage will prevent the nozzle sealing, causing foam to leak out. This in turn will depressurise the gun, allowing air to get in, so the foam will begin to set and the gun will become blocked. Prior to use the tip will require cleaning, this is best done carefully with a Stanley knife once the foam on the nozzle has set.

The pin is pulled by the trigger, opening the nozzle and is regulated by the lock-off screw. Unwinding the screw unlocks the trigger: the more it is unwound the faster the foam can flow. When you have finished, the screw should be closed to seal the gun. The screw firmly shuts off the nozzle and prevents the trigger from moving. After storage the pin in the nozzle will be stuck in place, the lock-off screw will need to be unwound enough to sufficiently break the seal.

The first squeeze on the trigger is best done into a refuse bag or large void. This is because when the seal is broken, a burst of foam is delivered before the trigger can regulate the appropriate flow. If the nozzle doesn’t close off immediately, quickly close the lock-off screw to stop the gun.

The foam canister is screwed onto the gun via the inlet valve which opens the can. When the empty can is removed, the valve stops the foam returning back out of the gun. With time, the inlet valve can begin to fail and the foam will leak back. This depressurises the gun, allowing air to get in, the foam begins to set and the gun will become blocked. Always keep a canister on the gun and replace the canister as soon as it is empty.

The canister contains polyurethane filler and a propellent. The gun needs to be underneath the canister so the propellent will push the filler into the gun. If the canister is lower than the gun, the propellent will be lost. Once the propellent has escaped, the foam filler will be trapped and the canister will be rendered unusable. Low temperatures also inhibit the propellent; if the canister has been stored in a vehicle or outbuilding, bring it to room temperature before use. Shake the canister before and during use. Always read the label.

Canisters of cleaner can also be fitted to periodically flush the gun through, perhaps each time the foam canister is replaced. Although expensive, they are recommended not only to keep the gun working at its best and prolong its life, but also in a sticky situation: cleaner can salvage items of clothing as well as carpets etc.



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