Donate to Remove ads

Got a credit card? use our Credit Card & Finance Calculators

Thanks to johnstevens77,Bhoddhisatva,scotia,Anonymous,Cornytiv34, for Donating to support the site

Expanding foam and UPVC windows

Does what it says on the tin
JessUK98
Lemon Slice
Posts: 305
Joined: November 4th, 2016, 9:10 am
Has thanked: 87 times
Been thanked: 83 times

Expanding foam and UPVC windows

#431406

Postby JessUK98 » July 30th, 2021, 10:55 am

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?

redsturgeon
Lemon Half
Posts: 8911
Joined: November 4th, 2016, 9:06 am
Has thanked: 1309 times
Been thanked: 3667 times

Re: Expanding foam and UPVC windows

#431409

Postby redsturgeon » July 30th, 2021, 11:04 am

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

JessUK98
Lemon Slice
Posts: 305
Joined: November 4th, 2016, 9:10 am
Has thanked: 87 times
Been thanked: 83 times

Re: Expanding foam and UPVC windows

#431413

Postby JessUK98 » July 30th, 2021, 11:12 am

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?

redsturgeon
Lemon Half
Posts: 8911
Joined: November 4th, 2016, 9:06 am
Has thanked: 1309 times
Been thanked: 3667 times

Re: Expanding foam and UPVC windows

#431415

Postby redsturgeon » July 30th, 2021, 11:20 am

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

redsturgeon
Lemon Half
Posts: 8911
Joined: November 4th, 2016, 9:06 am
Has thanked: 1309 times
Been thanked: 3667 times

Re: Expanding foam and UPVC windows

#431418

Postby redsturgeon » July 30th, 2021, 11:27 am

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

JessUK98
Lemon Slice
Posts: 305
Joined: November 4th, 2016, 9:10 am
Has thanked: 87 times
Been thanked: 83 times

Re: Expanding foam and UPVC windows

#431423

Postby JessUK98 » July 30th, 2021, 11:35 am

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.

JessUK98
Lemon Slice
Posts: 305
Joined: November 4th, 2016, 9:10 am
Has thanked: 87 times
Been thanked: 83 times

Re: Expanding foam and UPVC windows

#431430

Postby JessUK98 » July 30th, 2021, 11:52 am

Image

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.

ReformedCharacter
Lemon Quarter
Posts: 3120
Joined: November 4th, 2016, 11:12 am
Has thanked: 3591 times
Been thanked: 1509 times

Re: Expanding foam and UPVC windows

#431438

Postby ReformedCharacter » July 30th, 2021, 12:07 pm

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

JessUK98
Lemon Slice
Posts: 305
Joined: November 4th, 2016, 9:10 am
Has thanked: 87 times
Been thanked: 83 times

Re: Expanding foam and UPVC windows

#431444

Postby JessUK98 » July 30th, 2021, 12:20 pm

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.

redsturgeon
Lemon Half
Posts: 8911
Joined: November 4th, 2016, 9:06 am
Has thanked: 1309 times
Been thanked: 3667 times

Re: Expanding foam and UPVC windows

#431448

Postby redsturgeon » July 30th, 2021, 12:25 pm

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

JessUK98
Lemon Slice
Posts: 305
Joined: November 4th, 2016, 9:10 am
Has thanked: 87 times
Been thanked: 83 times

Re: Expanding foam and UPVC windows

#431456

Postby JessUK98 » July 30th, 2021, 12:42 pm

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 :lol:

AJC5001
Lemon Slice
Posts: 447
Joined: November 4th, 2016, 4:55 pm
Has thanked: 161 times
Been thanked: 158 times

Re: Expanding foam and UPVC windows

#431493

Postby AJC5001 » July 30th, 2021, 2:41 pm

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

AsleepInYorkshire
Lemon Half
Posts: 7383
Joined: February 7th, 2017, 9:36 pm
Has thanked: 10514 times
Been thanked: 4659 times

Re: Expanding foam and UPVC windows

#431536

Postby AsleepInYorkshire » July 30th, 2021, 5:38 pm

JessUK98 wrote:Image

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.

The windows not correctly sized.

AiY

88V8
Lemon Half
Posts: 5769
Joined: November 4th, 2016, 11:22 am
Has thanked: 4098 times
Been thanked: 2560 times

Re: Expanding foam and UPVC windows

#431563

Postby 88V8 » July 30th, 2021, 7:04 pm

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

JessUK98
Lemon Slice
Posts: 305
Joined: November 4th, 2016, 9:10 am
Has thanked: 87 times
Been thanked: 83 times

Re: Expanding foam and UPVC windows

#431579

Postby JessUK98 » July 30th, 2021, 8:35 pm

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 :lol:

AsleepInYorkshire
Lemon Half
Posts: 7383
Joined: February 7th, 2017, 9:36 pm
Has thanked: 10514 times
Been thanked: 4659 times

Re: Expanding foam and UPVC windows

#431580

Postby AsleepInYorkshire » July 30th, 2021, 8:37 pm

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 :lol:

So the old windows were too small too

AiY

JessUK98
Lemon Slice
Posts: 305
Joined: November 4th, 2016, 9:10 am
Has thanked: 87 times
Been thanked: 83 times

Re: Expanding foam and UPVC windows

#431583

Postby JessUK98 » July 30th, 2021, 9:01 pm

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 :lol:

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!


Return to “Building and DIY”

Who is online

Users browsing this forum: No registered users and 11 guests