Can I fill a metal window lintel with expanding foam?

[MrsRenovator]

I've just chipped some of the plaster from the top of a cold window reveal. Above the 10mm of plaster there is a perforated metal window lintel. Icy cold. Also blowing Icy wind though it. No wonder there's so much condensation! Fitted in the early 80's.

When I do the internal insulation is there any reason why I can't fill the lintel with expanding foam?

What do you think?

 

[crank39]

Won't hurt, new builds have cavity closers on 4 sides to stop this, wouldn't hurt you doing top and both sides if your decorating at some point

 

[MrsRenovator]

Ah thank you. Makes you wonder why no-one had thought of the importance of insulation back then.Or did we all just expect to be cold through the winter and wear wooly jumpers? I remember it always being freezing in our house.

Anyway, when I have removed all the plaster from the reveals I'm hoping to get 10mm of aerogel blanket in there. I hope it will adhere to the metal lintel ok. But i will still be short of space for the PB. I'm looking at 6mm cement board. or 3mm if i could find a supplier. Can't think how to fix it to the top reveal tthough. Looks like its going to be mainly instastik at the moment.

 

[crank39]

Clean the dust off the board and use either pinkgrip or a polymer based grab adhesive

 

[MrsRenovator]

 

[MrsRenovator]

If I use aerogel blanket on the top reveal, how will I attach the pb/Mg0? Can I use adhesive in both layers?