On Wednesday, August 21, 2013 8:40:58 PM UTC+1, GMM wrote:

I decided a while ago to renovate (rather than replace) the sash windows
on my victorian house.[1]
One of the first issues I cam across was the size of the (vertical) gaps
between the frames and the brickwork in many cases: Far too wide
(~15mm) for a normal dollop of sealant. Presumably these were
originally sealed with a fillet of mortar or something.
Anyway I decided that these would be best covered with a strip of
moulding and have been painting the mouldings off the job to make it
easier. Now they're ready, the question arises of wehther I should just
put these on and seal up or whether the fairly substantial void behind
them (15mm wide but a couple of inches deep to sound but weathered
timber)would benefit from judicious application of expanding foam, as
normally used to fix windows etc these days.
I know PVCu box sash windows shouldn't be fixed with foam as the
expansion can distort them, but what about timber? Any views or
experience chaps?

I'd just use a suitable filler rather than mod the frames. The 20th century option is sand/cement, an older option is burnt sand mastic. I certainly wouldnt use expanding foam. A bunch of sideways forces on a wood frame, and something that doesnt let any moisture dry out is not something I'd do.

Sounds like somewhere along the line you're missing something. What you proposed should flag up as an inappropriate approach very quickly. Vic house technology is very well proven, you just need understand and apply it rather than create horrible modern bodges.


NT