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.