How to Use an Expanding Foam Gun (& Which to Buy)
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An expanding foam gun (also called an applicator gun) is a metal tool that screws onto a gun-grade foam can and lets you lay a neat, controlled bead with one hand. It is far more precise and far less wasteful than a hand-held can with a plastic straw. You screw the can on, purge a little to prime it, and dispense with the trigger. The key habit: leave the can attached between uses so the foam does not cure inside, and flush the gun through with foam gun cleaner when you change cans or finish for the day. A basic professional gun is around £20.
What is an expanding foam gun, and why use one?
A foam gun is a reusable applicator for PU expanding foam. The can screws onto a threaded collar at the top, and a trigger with an adjustable flow screw controls exactly how much foam comes out of the long barrel. Compared with a hand-held can and its throwaway straw, a gun gives you:
- Control. A fine, steady bead you can feather into a joint, instead of the all-or-nothing blast of a straw.
- Less waste. The can stays usable over days or weeks because it is sealed on the gun, rather than curing off once you have cracked a straw can.
- Reach and one-handed use. The long barrel gets into gaps a straw cannot, and you keep a hand free.
For anyone using foam regularly, a gun pays for itself quickly in foam you are not throwing away.
Gun-grade foam or hand-held foam: which do you need?
This trips people up, so get it right before you order. There are two types of can, and they are not interchangeable:
| Gun-grade foam | Hand-held foam | |
|---|---|---|
| How it applies | Screws onto a foam gun | Plastic straw clips on the can |
| Needs a gun? | Yes | No |
| Best for | Regular use, neat work, less waste | One-off jobs, occasional use |
So if you buy a gun-grade can, you must have a gun to fit it to. If you only need foam once, a hand-held can with the straw is fine. If you are filling gaps week in, week out, buy the gun and gun-grade cans from the foam range. The same gun is what you use to apply plasterboard adhesive foam too.
Which foam gun should you buy?
A basic professional gun does the job for most trades. The Soudal Professional PU Foam Gun is around £19.99. When you are choosing one, look for:
- An all-metal body and barrel. Cheap part-plastic guns crack and seize. A metal body lasts.
- An adjustable flow screw at the back, so you can dial the bead from a fine line to a full fill.
- A PTFE or coated barrel if you can get it, cured foam releases more easily and it cleans up better.
If you are starting from nothing, a kit like the Soudal Foam Filler Kit pairs the gun with gun-grade foam and a cleaner in one go, so you are not buying the three pieces separately. Either way, buy the cleaner at the same time, you need it to hand, not ordered after the foam has set in the gun.
How do you use a foam gun?
Step One: shake and fit the can
Shake the gun-grade can hard for 20 to 30 seconds, foam that is not shaken comes out thin and cures poorly. Hold the gun upright and screw the can onto the collar until it seats. Keep the gun pointed away from you and never at your face while you do this.
Step Two: purge and set the flow
With the can now upside down (can on top, barrel down) turn the flow screw in, then squeeze the trigger to purge a small amount into a waste bag until foam runs steadily. Back the flow screw out to set the bead size you want. Work with the can inverted throughout, that is how the gas pushes the foam.
Step Three: dispense the bead
Squeeze the trigger gently and lay the foam. Expanding foam grows as it cures, so fill a gap around half to two-thirds full and let it expand to fill the rest, overfill and you are trimming it back later. For deep gaps, lightly misting the surface with water first helps the foam cure right through.
How do you clean and store a foam gun?
This is the part that decides whether your gun lasts years or dies in a week, so it matters more than the gun you buy.
- Between uses on the same job, leave the can attached. A charged gun with the can on and the flow screw closed will sit for days or weeks ready to go. The foam only cures if air gets to it, so keeping the can on seals the gun.
- When you change cans or finish, flush it out. Take the empty can off, screw a can of foam gun cleaner (around £5.40) onto the collar, and trigger it through until it runs clear. The cleaner is the same PU solvent the foam is based on, and it dissolves uncured foam out of the barrel and valve.
- Never let foam cure inside the gun. Cured foam in the barrel is the one thing you cannot flush out. Once it has gone off in there, the gun is usually finished.
Do that and one gun outlives a lot of cans. The cleaner is cheap insurance, always have one on the shelf.
How much does a foam gun cost?
| Item | Typical price |
|---|---|
| Professional PU foam gun | around £19.99 |
| Foam gun cleaner (500ml) | around £5.40 |
| Gun and foam and cleaner kit | see the kit page |
So for around £25 you have a gun and a cleaner that will see you through job after job, plus the gun-grade foam per can. Prices are correct at the time of writing; check the foam guns page for live pricing. All come with fast UK delivery.
Common mistakes to avoid
- Letting foam cure in the gun. The single biggest killer of foam guns. Leave the can on between uses, and flush with cleaner when you are done.
- Taking the can off "to be safe". Backwards. An empty collar lets air in and cures the foam in the valve. Keep a can on it.
- Not shaking the can. Unshaken foam is weak and sticky and cures badly. Shake it hard first.
- Overfilling the gap. Foam expands. Fill halfway and let it grow, or you are cutting it back.
- No cleaner on site. By the time you have ordered one, the gun has set solid. Buy the cleaner with the gun.
The short version
A foam gun screws onto a gun-grade foam can and gives you a controlled bead with far less waste than a straw can. Shake, fit the can, purge, and dispense with the can inverted, filling gaps halfway and letting the foam expand. Leave the can on between uses and flush the gun with cleaner when you change cans or finish, never let foam cure inside. A pro gun is about £20 and a cleaner £5.40. Get them from the foam guns range, or the all-in-one kit.
By Steve, Builders Hardware Direct. Steve runs the BHD trade counter and has spent years supplying foams, guns and sealants to builders and installers across South Wales. Not sure which gun or foam you need? Call the counter on 01269 267030 or order online for fast UK delivery.
