Expanding Foam for Replacement Window

[Omits]

I am replacing an old wood one with a 2nd have UPVC but it is 5 - 10mm smaller. Can I use foam to fix the window? It will sit on the outer leaf and I guess the foam will spill out then show after it has bee cut off. Advice on how to finish appreciated.

PS which foam from Screwfix is best for this?

 

[Mark DM]

If the frame is only 5 -10mm smaller then that's 3 -5mm a side clearance. You would struggle to even get a nozzle in and most of the foam will end up on the face. I would screw and plug it or use frame fixings if preferred. Silicon up the joint to seal it.

 

[luna19]

Is it 5to 10 mm smaller both sides or the frame or overall 5 to 10 mm smaller. if the latter expanding foam will work ,mask up the window frame to avoid foam on the plastic frame then once dry use plastic trims to cover foam

 

[BuildingMad]

The gap is required for expansion anyway so avoid any hard filling.
Use some of this followed by silicone.
https://www.ebay.co.uk/itm/154691090071

 

[Jord86]

I am replacing an old wood one with a 2nd have UPVC but it is 5 - 10mm smaller. Can I use foam to fix the window? It will sit on the outer leaf and I guess the foam will spill out then show after it has bee cut off. Advice on how to finish appreciated.

PS which foam from Screwfix is best for this?

Yes you can use foam to fix the window, buy a gun and a ‘regular’ tin of gun grade foam as you will have far more accurate control over it. If you specifically don’t want fixings in the window then use timber wedges to position the window correctly then foam it up. Once the foam is cured, cut off any excess then silicone all around, and under the cill too.