Expanding Foam in Cavity Wall Mistake

damyan24 · Post by **damyan24** » Mon Nov 09, 2020 6:08 pm

I am a landlord and my tenants experienced issues with damp on the inside of a bay window and it didn't seem like there was an issue with condensation or ventilation (as is usually the case). I noticed a crack where the bay window render meets the brickwork on the outside of the house and thought it may be causing the issue.

I thought I would fill the gap with an all-weather sealant in case this was the cause of the damp. The gap at the top (just above where the arrow is pointing) was fairly big (around 0.5-1cm) so I thought I would use some expanding foam first. Now, what I didn't realise was that the gap was essentially leading straight to the wall cavity so all of the foam just fell down (750ml can). I only then realised it may have actually been a big (and very silly) mistake which could potentially lead to more issues.

I wanted to know if this is something I should worry about and whether there is anything I should do now before I experience any issues with that?

ahfix · Post by **ahfix** » Tue Nov 10, 2020 10:01 am

The foam has probably fallen into the void, I doubt it's going to do anything.

However, I *think* the issue with the damp is due to the render on the bay, it's at ground level allowing the damp from the earth to rise up (you can see staining at ground level).

Quick fix could be to dig a small trench around the bay so the render isn't touching the ground, longer term fix is to cut away a few inches of the render to prevent it happing again.

ah

Argyll · Post by **Argyll** » Tue Nov 10, 2020 11:55 am

ahfix wrote: ↑Tue Nov 10, 2020 10:01 am The foam has probably fallen into the void, I doubt it's going to do anything.

However, I *think* the issue with the damp is due to the render on the bay, it's at ground level allowing the damp from the earth to rise up (you can see staining at ground level).

Quick fix could be to dig a small trench around the bay so the render isn't touching the ground, longer term fix is to cut away a few inches of the render to prevent it happing again.

ah

He could use a chemical DPC. You drill a hole every foot or so and insert a DPC stick. Skill builder has a video on YouTube for it.

Argyll · Post by **Argyll** » Tue Nov 10, 2020 11:56 am

wes56 · Post by **wes56** » Fri Nov 20, 2020 4:44 pm

I thought i posted a reply to this thread on 9th or 10th nov but whats happened to it i dont know?

No need for trenches. Just cut the render about 80mm to 90mm above ground contact. Make sure you are cutting above the Dpc thats been bridged by the low render.
Use Polyurethane sealant to seal up any gaps or cracks in the render.

You've got cavity walls so you might have cavity insulation thats got soaked from the damp.
You might also have a rubble fill in the cavity, the rubble will also bring up bridging damp.
The only way to know for sure is to take out a few bricks and have a look.
If damp has gone through the inside wall surface then you should look into the cavity. The joist might also be at risk.
Can you post a photo showing inside at the skirting level.