Filling/sealing foam for upvc window frames

17 Apr 2007
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United Kingdom
20 year old frames. I've removed the old sealant on the outside and there is a frame/wall gap of about 1/4".

I've seen this foam on the SF website. Just want to know if its suitable for window frame/wall gap filling. Any opinions please!

I can flush the foam to the frame face then run a fresh silicone bead over it to weather seal.
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As per above, if you aren't used to using expanding foam, you risk applying too much.

If you are willing to pay for a foam gun, you will be able to apply the foam (low expansion or not) with vastly greater accuracy.

I recently purchased a cheapie gun for £12 (incl delivery) from Amazon. It isn't brilliant but it has removable nozzles that allow me to squirt foam in to 2mm holes. Naturally, it means that you have to purchase gun grade cans of foam.


With a gun you should be able to get a pretty level finish. If you are worried about applying too much, run a line of masking tape on the bricks first. Once the foam has cured you can use a snap off blade to cut away the excess foam and tape, before "caulking" it.

In the past, I have left cans of expanding foam connected to guns for over 6 weeks. They were still usable but I had to scrape the metal nozzle with a small screwdriver to free up the pin. A non gun grade can, I expect to throw away after 2 or three weeks.

If you purchase a gun, also spend £6 on a can of gun cleaner- it is basically acetone, but if you make a mess, it will clean that mess up.

If you want to use white silicone, you may need to undercut the foam (so that it is a couple of mm bellow the surface)- If the silicone seal is thin, you risk seeing the foam colour under it.

BTW, expanding foam is water proof, but UV light makes it become brittle.

Spray the areas to be filled with a mist of water. It will increase both adhesion and curing times.
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I found this Soudal aerosol version. I'll spray a bit on a board first to get an idea of the expansion.

I am not sure that will provide an accurate gauge of expansion. It you run a bead on a scrap bit of wood, the foam will be able to expand in 3 directions (actually 4). In a cavity, if you fill from top to bottom, it can only expand in two directions, meaning that the expansion will be greater (in those two directions).

I would recommend that you apply less than will eventually be required. You can always top it up once it starts to skin. Drape a bin bag over the edge of the window sill to protect the sill. The PU foam will not stick to bin bags (poorly phrased, it will stick but none will be left on the bin bag as you peel it away).

Best of luck.
I've tried the Soudal Window/Door aerosol and I'm not impressed. Tried a test bead on a bit of wood yet didn't any obvious expansion although the instructions say to wet surfaces with a fine water mist to help it cure.

I may just used upvc exterior sealant fill the wall/frame gap.
You... Set your gun to the right size for the requirement? ???

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