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Expanding foam and UPVC windows
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- Lemon Slice
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Expanding foam and UPVC windows
Just curious really about peoples thoughts on this. I’m having my house repointed in lime mortar and they are doing the window reveals as well. They’ve hacked all the old lime mortar away and they commented that there’s no expanding foam around the windows, apart from one which has foam only down one side.
I have an old stone house, is there a reason why there would be no expanding foam? I’ve read various things like expanding foam distorts the frame etc. These guys say that the window fitters they know always put expanding foam around the windows for insulation. So, should I get them to just plaster around the windows in lime mortar or let them put some expanding foam in first?
I have an old stone house, is there a reason why there would be no expanding foam? I’ve read various things like expanding foam distorts the frame etc. These guys say that the window fitters they know always put expanding foam around the windows for insulation. So, should I get them to just plaster around the windows in lime mortar or let them put some expanding foam in first?
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- Lemon Half
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Re: Expanding foam and UPVC windows
I can't see expanding foam distorting the frame, it will have plenty of space to expand all around the gap, it's not like you are forcing it into an enclosed space with no exits. Once the foam has set it will also be perfectly compressible to allow expansion of the windows with heat. When I fitted a UPVC window to the rear of my house I used foam and have no problems. The foam should be cut back to below the frame thickness and the gap filled with low modulus silicone filler.
John
John
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- Lemon Slice
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Re: Expanding foam and UPVC windows
redsturgeon wrote:I can't see expanding foam distorting the frame, it will have plenty of space to expand all around the gap, it's not like you are forcing it into an enclosed space with no exits. Once the foam has set it will also be perfectly compressible to allow expansion of the windows with heat. When I fitted a UPVC window to the rear of my house I used foam and have no problems. The foam should be cut back to below the frame thickness and the gap filled with low modulus silicone filler.
John
What about the window shims? Won’t the expanding foam potentially disturb the shims making them go out of shape?
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- Lemon Half
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Re: Expanding foam and UPVC windows
I think you may be over estimating the pressure exerted by expanding foam. It is important to fill the gap around the window with foam to maintain the thermal performance of the window. This material needs to be compressible to take up the expansion and contraction of the window with temperature changes, The combination of expanding foam and low modulus silicone fulfils this brief. Without filling the gap with these materials or similar you will get cracking and draughts.
John
John
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Re: Expanding foam and UPVC windows
If you fill an open paper bag with expanding foam will it:
a. pop the bag?
b expand out of the top of the bag?
John
a. pop the bag?
b expand out of the top of the bag?
John
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- Lemon Slice
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Re: Expanding foam and UPVC windows
Well they’ve just hacked off the reveals for the downstairs windows and they have expanding foam around them. The upstairs windows have much bigger openings by the looks of things. They are going to put some foam around the upstairs windows. Said something about dabbing it around the frame as the foam will expand upwards, and they are going to have to do the render the reveals in layers as the original is quite thick.
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- Lemon Slice
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Re: Expanding foam and UPVC windows
This is basically what I’m talking about. Much bigger gaps that have no foam, whereas downstairs windows, gaps aren’t as wide and have foam around them. Only one of the three upstairs front windows has foam, and only down one side. No idea why it would have been done like this.
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- Lemon Quarter
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Re: Expanding foam and UPVC windows
I'm having new uPVC doors and windows fitted at the moment. Plenty of expanding foam, caulk and silicone. The fitters have done well so far given that the mains supply, fibre broadband and phone line were fitted through the front door frame. Still all working so far
RC
RC
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Re: Expanding foam and UPVC windows
The top does seem to have wider openings than the bottom, the guys here doing the repointing did say they could have made the windows a little bigger. I’m wondering if they just sized up based on the previous windows, and didn’t want to make the top windows bigger than the bottom windows or it would have looked odd.
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- Lemon Half
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Re: Expanding foam and UPVC windows
JessUK98 wrote:The top does seem to have wider openings than the bottom, the guys here doing the repointing did say they could have made the windows a little bigger. I’m wondering if they just sized up based on the previous windows, and didn’t want to make the top windows bigger than the bottom windows or it would have looked odd.
Usually you would size up to allow approx 10mm gap all round. Perhaps they were bought in standard sizes rather than made to measure.
Get that expanding foam in there! Job done!
John
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- Lemon Slice
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Re: Expanding foam and UPVC windows
Just taken them out a cup of tea and they are having fun with the expanding foam. Bet they are secretly cursing for taking this job on
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- Lemon Slice
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Re: Expanding foam and UPVC windows
JessUK98 wrote: No idea why it would have been done like this.
I'd guess that the installers ran out of foam due to having bigger gaps to fill and couldn't be bothered to go and get more as it would delay the completion and they' be late home for tea.
Adrian
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- Lemon Half
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- Lemon Half
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Re: Expanding foam and UPVC windows
JessUK98 wrote:I’m having my house repointed in lime mortar ...
If I were doing that with a period house, I would be getting shot of the plastic windows....
We had some new (custom, wooden) windows fitted, the fitter, who does nothing but fitting for a living, used a mix of mechanical fixings and foam. I think had he been left to himself it would just have been the foam, he said it is plenty strong enough but with me breathing down his neck he agreed to put some screws in as well.
The chap who made the windows was quite obsessive about sizing and came back three times to measure and re-measure. They were almost too big, but not quite.
It's lucky the weather has cooled, lime mortar does not like heat, it needs a long curing time.
V8
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- Lemon Slice
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Re: Expanding foam and UPVC windows
I think the problem is that unless you hacked away all the mortar from the reveals first, you’d never know there was such a large gap. So they’ve measured based off the old windows. The reveals were proper thick. Obviously had to be to cover the gap
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- Lemon Half
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Re: Expanding foam and UPVC windows
JessUK98 wrote:I think the problem is that unless you hacked away all the mortar from the reveals first, you’d never know there was such a large gap. So they’ve measured based off the old windows. The reveals were proper thick. Obviously had to be to cover the gap
So the old windows were too small too
AiY
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- Lemon Slice
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Re: Expanding foam and UPVC windows
AsleepInYorkshire wrote:JessUK98 wrote:I think the problem is that unless you hacked away all the mortar from the reveals first, you’d never know there was such a large gap. So they’ve measured based off the old windows. The reveals were proper thick. Obviously had to be to cover the gap
So the old windows were too small too
AiY
Yep. At least the top 3 windows were. The downstairs windows had much smaller gaps. The whole house is frankly just just wonky. I don’t think any of the walls are straight. The deeds say it was built “pre 1820” so it’s just a nightmare, sometimes I regret starting stuff. The electrics will need doing at some point, dread to think what that will find!
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