Expanding Foam in Cavity Wall

[DaveWave]

I was looking for some advice…

We’ve recently done some renovations to a Bolton extension at the side of the house which has left the floor level lower than it used to be and has exposed “holes” underneath the patio doors that just run into the wall cavity.

Sadly this week we’ve had mice gain access to the room via the wall cavity and so as a knee jerk reaction we blocked the holes with expanding foam.

(I’m aware we also need to tackle where the mice are getting in from outside.)

However, we might have gone a bit gung-ho with the foam and we can’t see how far the foam has expanded into the cavity.

In hindsight, I’m now concerned that this area will be a bridge from the outer wall to the inside and cause damp.

Is this a concern? Or as it’s a smallish area, is it possibly okay? I don’t relish trying to dig the foam out of the cavity but would rather know now than face a bigger issue down the line.

 

[Ivor Windybottom]

I wouldn't worry. It's a theoretical risk, in reality very unlikely.

It won't wick moisture but may randomly form itself into a shape that somehow funnels condensation off the back off the outer towards the inner wall. In reality you probably won't have water in there anyway, and the chances of this actually happening are near zero.

But I still wouldn't squirt it into cavities in future.

 

[Notch7]

However, we might have gone a bit gung-ho with the foam and we can’t see how far the foam has expanded into the cavity.

In hindsight, I’m now concerned that this area will be a bridge from the outer wall to the inside and cause damp.

spray foam I believe is closed cell and doesnt transmit damp, although if youve made a path for actual water to run across that might allow the inside skin to get wet

 

[DaveWave]

Thanks for the replies. That’s a bit of a relief.

There shouldn’t be any water around there so hopefully it’ll okay.

And I was kicking myself almost as quickly as I was spraying foam so I won’t do it again.

 

[Ivor Windybottom]

There are companies who will fill your entire cavities with the stuff. Opinions differ!

I'm not sure whether it will or won't wick moisture. It's plastic, but full of bubbles. I've seen it soak up water like a bath sponge before.