Best Type Of Expanding Foam For UPVC Windows?

13 Sep 2010
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Wrong side of The Channel
United Kingdom
I'm about to fit a couple of new UPVC windows into brick openings. I remember reading somewhere that it's not a good idea to use standard expanding foam for the gap between the frame and brickwork, because it expands too much and can distort the UPVC frame.

I seem to remember them suggesting a foam that doesn't expand quite so much. Can anyone recommend one, or am I worrying to much about this?

Thanks for any advice and help.
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I have only used the type that you look at just after spraying and think, "nah it's not enough" before turning your back on it and then discovering a foam monster coming for me!...

But yes there are types that expand much less than the most fearsome stuff...

Am sure I heard of expanding foam pushing walls over once upon a time..

Thinking of all the foam monsters I have known of, I perhaps should have gotten some..
I use the method of drilling several holes, about six inches apart vertically, starting with the bottom one and waiting for it to finish growing before doing the next one up. If it expands more than you were expecting it will come out of the hole above, so you skip that, and do the next clear one. If you are working right and left alternately, it gives time to expand.

use lots of clingfilm to prevent it sticking to the wall or frame.

If you are injecting into an open cavity, wrap a batten in clingfilm, nail or wedge it to cover the gap, and inject through holes drilled in the batten. By loosening the film you can remove the batten afterwards without it being stuck fast.

Spraying water into the gap first speeds up the swelling and the formation of a crusty skin.
Thanks for both of your replies.

Magiclintel's suggestion of the Exact Gap foam seems just what I want. Only expands as far as you want it, and doesn't keep expanding after application. Will give it a go.

Thanks also to JohnD for some suggestions that I wouldn't have thought of. Will be utilising some of the wife's cling film just in case the foam goes where it shouldn't.

Thanks all.
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I have used the exact gap foam in a tin before and found it creates a smaller Foam monster. The best thing I have used was a proper foam gun and normal gun grade foam. It's miles more controllable, like epically different to cans of stuff.

I imagine gun grade low expansion foam would be even better!
How did fitting the windows go in the end? any tips?

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