To fill or not to fill?

Question

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?

[1] On the topic of refurbishing windows, I took a trip to Reddiseals, who aren't far from me. Spent a lot more time there than I had planned chatting with their man who clearly knows his stuff. Spent a bucket of money too(!) but more importantly changed the approach. I'm sure there are other good places, but their stock is pretty impressive and advice is well informed. No connection, etc, but I'm sure I'll be over there again before too long. What amazes me, though, is why at least some of the seals and bits aren't stocked by the sheds. Surely there must be plenty of demand.

Scott M · Accepted Answer

When I first started playing DIY as a teenager in the late 80s, when B&Q was the same as Homebase, etc, I could never get my head round that they never seemed to have a cohesive range of, say, plumbing bits. In time a) B&Q got better and b) I realised that the stock wasn't what was needed so much as "what people (randomly) bought" and therefore what got re-ordered.

Murmansk · Answer

If you were to put expanding foam in there isn't there a danger that it might interfere with the weights on ropes that counterbalance the sashes?

Jim K · Answer

15mm? Too big?? Probly originally sealed with red mastic. No real biggy just use frame sealant in two passes if necessary. Jim K

meow2222 · Answer

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 w ouldnt 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 pro posed should flag up as an inappropriate approach very quickly. Vic house t echnology is very well proven, you just need understand and apply it rather than create horrible modern bodges.

NT

To fill or not to fill?

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