Ideas sought for sealing gap in upvc double glazing lip

[jkn]

Now that I am working in the 'back bedroom' I am becoming more keenly awar of the draughts in there...

There seem to be two main causes. One is a gap between the opening window and the frame (it's not 'pulling to' fully). That I will take a look at shortly. But the one I want to ask about is a gap between the uPVC frame and the window cill.

This gap is pretty narrow but I think is where the cold air is coming in (from the cavity?). The inside of the frame has a hollow 'lip', about 2" wide by 1/2" deep, the lipped edge of which is supposed to be in contact with the top of the cill; but it is a few mm clear.

I can apply some sealant but because it is basically a crack, with nothing behind, I am dubious that this will be a reliable seal. The nuclear option is trying to squirt some expanding foam into volume behind the lip, but I really don't want to try that. Is there anything else I can do to improve my chances of sealing this gap?

Thanks, J^n

[Tricky Dicky]

Go to your local DG material supplier and ask for a capping strip these come in various widths and the double glazers use them to cover any unsightly gaps usually between frame and reveal where plaster gets damaged removing old frames. I have a couple in precisely the same situation as yours.

The strips are normally secured with double sided tapes and finished off with a thin fillet of silicone the same supplier should be able to give the right tape which needs to be the foam backed type not the sellotape thin stuff.

Richard

[Harry Bloomfield, Esq.]

It happens that Tricky Dicky formulated :

Eurocell - They have an online presence and lots of local outlets.

[jkn]

Hmm - it is probably the very same 'capping strip' that I am referring to as the 'lip'. I suspect it was applied when these frames were retro-fitted to the property (before my time here).

My 'capping strip' seems to be solidly fixed to the main window frame. I am not sure how it is fixed - glue, perhaps.

I suppose I could either experiment with removing that where it joins the window, and/or putting a larger capping strip over the current one. I can see where there used to be a fillet of silicone which is no longer present. It's either just disintegrated or shifting window cill etc. has caused it to fail.

Food for thought, thanks.

J^n

[Tricky Dicky]

I think you will find it is double sided tape not glue simply easier and quicker for the installers to do it that way no waiting for glue to set. It is surprising how well it sticks it was certainly the case with our windows. We had some old uPVC windows replaced that had too narrow an air gap with external beads which still used the old wooden interior cills with a wooden fillet strip to span the gap. The new windows had a covering cill (actually fascia board) siliconed over the top of the wooden cill a capping strip was used to fill the gap. How did I know it was taped on? A roofer put his foot through the bedroom ceiling and a falling piece of PB put a large dent in my brand new cill which subsequently was replaced.

Richard

[Martin Brown]

The simplest temporary solution to possibly both of these is a length of shrink wrap tubing which is soft enough to push into position and pliable enough to make a reasonable seal. Temporary fix try cardboard.

You can get P or W profile soft foam tape with a sticky back for making good an opening window seal. Easier than tweaking hinges in mid winter.

It is rather hard to visualise the profile you want to fill. But a first try with a piece of folded paper will quickly establish if that is where the cold draft is coming from.

Sealant is usually well behaved for gaps narrower than about 5mm. Much beyond that you might find that it is unwilling to bridge the gap.

[jkn]

I confess that I have been considering cardboard, as you say for a temporary fix, myself...

The profile is a bit like an 'el', or hockey stick shape - mostly flat with a small lip at the end. I am pretty sure a goodly proportion of the draught is coming from there.

Yeah. I am thinking that I could use two applications of sealant; one to be pushed back mostly 'inside' the gap. Then when it has dried it will form a rear surface for the second application to be pressed against, if that makes sense...

J^n

[Andrew]

I watched a local firm replace windows over the road. They glued the trim strips on with superglue, then ran a bead of clear mastic at the junction between trip strip and brickwork. This covers the 5mm gap and hides any old paint splashes.

The internal trip strips are just to hide any damage they might have done to the plaster removing the old window. Quick'n'Dirty.

I watched Anglian do a similar 1970's property further down the road and they used expanding foam in the gap between frame and window reveal, then removed the excess and then fitted the trim strips. the expanding foam stops air leakage around the frame which is what the OP can detect.

He could just run some white silicone into the gap and smooth it off.

[RJH]

I'd be inclined to use low expansion foam, then sealant over that. Sealant on top of dried sealant doesn't sound ideal.

[jkn]

I do have a proper expansion foam gun ... is low expansion foam a very different thing than the 'normal' stuff? I have never knowingly used the former.

Would it be feasible to squeeze the tube down to 5mm or so to get the foam into the hollow area under the capping strip? It does seem that this would give a more 'structural' solution than just sealant alone.

I am in the process of cutting away the old sealant BTW, so it won't be sealant on sealant.

Thanks, J^n

[Brian Gaff (Sofa]

Is the upvc just a hollow U shape and bends when you put pressure on it, if so then I agree its going to be hard to fill it. If it seems pretty solid then sealant will work, indeed may be the only way. At least its relatively easy to get rid of if it fails.

One might have supposed whoever fitted it would have spotted this and put something in there to start with before finally fixing the frame in.

Its quite a common problem I've seen all sorts of things done, even a piece of wood screwed to the front flat face of the upvc with some kind of filler under it, but that depends on how extreme you want to get and whether you really want to have to paint it. Brian

[Murmansk]

I've seen a video on YouTube about expanding foam tape which is nothing to do with expanding foam as found in a can!

It's foam tape which is supplied in a flattened form and expands when you release it from the roll - used to seal the variable gap under a skirting board in the video I saw

[jkn]

A bit of an update - with a bit of judicious poking around I have determined that the capping strip ('45mm bull nose, perhaps) *is* probably superglued to the frame - I was prying at the wrong bit! I think with gentle application of a mallet & bolster chisel I can probably knock it off quite easily.

So that will make sealing it a lot easier - I can use low-expansion foam in any gap, then refit the capping strip as if from new (or even buy as new strip, gasp)

I've also realised that the gap in the window is where the rods stuck open some years ago, and I just fitted an espag handle 'temporarily'. That might be a real pain to fix, and it is on the first floor, sigh...

Anyway, thanks for all the thoughts and suggestions

J^n

[RJH]

I've got some of the Screwfix own brand cheapie in the gun right now, and it's what I'd call 'high expansion'. The lower expansion is easier to control I find. But I've just done a round of filling (foam into cavities/gaps then fine filler or caulk on top) and it's gone OK - just need to be sure the flow is just right for the gap you're filling.

Don't see why not. Maybe try a small area first?