Expanding foam in cavity wall

[floonds]

Hi all

We've recently purchased a three bed 1930s semi. The property has suspended timber floors and cavity walls which seem to be filled with PU foam.

We've just had an external doorway bricked up, and as such, there's now a void between the inner and outer leaf. I've read online and can't seem to find a definitive answer, but is it ok to fill this with 'off the shelf' expanding PU foam such as the No Nonsense stuff from screwfix ?

On another note, I had a look under the floor and it appears the foam has expanded over the air bricks - I assume this should be removed?


Thanks in advance for the help.

 

[JohnD]

Are you sure that bulge is an air brick? It might just be an open joint or crack in the brickwork.

Any airbricks must be clear and unobstructed to ventilate moisture out.

The pipes should be lagged, especially if they are close to an airbrick and icy winds can blow through.

 

[floonds]

Yeah it looks like it (visible from outside at this position)

Should have mentioned - central heating is new install and pipes will be lagged next week.

 

[JohnD]

I use expanding foam around windows and doorframes, and joists where they are built into walls. These are small gaps.

The problem with a large flat area like your cavity it that the foam expands, and cases have been reported where it can push apart the two surfaces. I would have been happier to build in an insulating slab during the build. If you decide to DIY, drill enough holes so that you can see the foam if it rises up and starts to bulge through a higher hole, and apply in enough layers that each can finish expanding and set before you apply the next.

It expands much more than you think.

 

[floonds]

Thanks for the advice, I thought that would be the case. The builder said the same and that's why he advised I do the foam once the mortar has dried.

I just wanted to check there were no absolute no-nos to using standard expanding foam in the cavity.

 

[vinn]

Are you saying, as it seems, that you have foam cavity wall insulation that was installed before you bought the house?
The cavity around air bricks and vents should have been sealed by the CWI installers to prevent insulation from blocking them.
Any & all air bricks will have to be examined and opened up if blocked off by insulation.
As above, you must have through ventilation under any suspended floors.

 

[vinn]

Has the inner skin at the doorway been built up yet - if not CWI beads might be used to fill the cavity as you build the inner skin up.
Or call Kingspan Tech Dept. for further advice.
There are claims that off the shelf (Builder's foam) has caused damp difficulties . Why that should be I dont know.

 

[floonds]

Are you saying, as it seems, that you have foam cavity wall insulation that was installed before you bought the house?
The cavity around air bricks and vents should have been sealed by the CWI installers to prevent insulation from blocking them.
Any & all air bricks will have to be examined and opened up if blocked off by insulation.
As above, you must have through ventilation under any suspended floors.

Yeah - we didn't think it had CWI until the plumber drilled through and found solid foam in the cavity. Upon closer inspection it's like this throughout the house. I'll have to check all the air bricks - that's the only one I can get access to at the moment