upvc window foam fixing - more details required

I have a window fixed in place etc, just need to fill gaps with "foam". Now, there are gaps around the window to allow for expansion, so presumably the foam must be flexible and rebound when pressed ? The foam I have is low expansion regular gap filler stuff, but it leaves an indentation when pressed. Surely this will just compress when the window expands, and then when the window shrinks again, it will leave gap behind ? Some recommend a latex foam, but I cannot find this in B&Q etc. Also, is a silicon seleant needed in front of the foam ? The gap at the top of the window is about 1.5 cms (used standard size window) - I cannot see how silicon could cover this gap, or how one could apply foam and leave a groove at the front for silicon.

In short - people just say "fill it with foam" without thinking about the mechanical properties, which I am sure leads to leaks etc. Can someone advise in more detail than "you wanna fill that with foam mate !" ?

TIA, Simon.

Reply to
Simon
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Sir

The foam fills the gap, I use the gap filler stuff screwfix sell, however its not the water/weater seal, for that jou silicone on some UPVC strips, avaiable from you local plastics company.

The foam I use, will degrage under UV light.

Rick

Reply to
Rick Dipper

You wanna fill that with foam, mate.

Then you wanna make good the outside, wither with render, or with PVC strips + silicone.

The foam is (more than) flexible enough to take up the expansion/contraction of the window. It will bond strongly to the window and the wall. But it doesn't form a watertight seal.

Reply to
Grunff

I filled mine with ordinary foam, then cut it back slightly. Finished with a mortar fillet with about a 5mm gap to the window. Filled this with white silicone. It's south facing and been fine.

IIRC, you can't leave foam exposed - it degrades in sunlight.

Reply to
Dave Plowman (News)

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