So I've just had the surveyor/estimator from the foam insulation company out to site today, and they say they can't do full fill foam injection because the outer leaf is stone with lime mortar, and the foam will cause cracks/bulges. They're now recommending bonded EPS beads.

 

This is *very* frustrating, as they never mentioned this previously, and the whole build detail was based on the fact the cavity would be foam injected. Two issues arise from this:

1) Airtightness - the blockwork, cavity to rafters closure, and joist penetrations all have relatively poor detailing, and the foam would've fixed all of that. However, I can at least remedy this by foaming all the joists gaps and top of cavity, and parging the blockwork.

2) Cavity trays - this is the bit that I'm struggling with. The house is a U shape, and the inside of the U has a flat roof. The cavity extends down below the level of the flat roof, and there are no trays fitted. Now we could pump the whole lot down to internal ceiling with EPS beads, but I worry that some moisture will find its way through, and we'll end up with wet patches on the plaster. Retrofitting cavity trays at the bottom of the stone leaf is so time/cost prohibitive at the moment that it's off the table.

 

I asked the company if they could foam fill up to the level of the flat roof, and then EPS, and they said absolutely not as they can't mix the two materials due to warranties etc. So it's up to me to sort out the prep/detailing.

 

I'm now thinking of using 1-part expanding foam to essentially create a full-fill cavity plug at the level of the flat roof, to act as a barrier to any moisture, with the EPS beads above it. It might not be as 100% impermeable as a cavity tray, but if any little moisture does end up in the cavity, it should stop it draining all the way to the bottom? 

 

We are not in an exposed location at all, and the inside of the U part of the building is even more sheltered.

 

Any clever thoughts?

 

Bugger. 

 

You've been let down here I feel. However it is what it is. 

 

I don't know your supplier but Walltite have a video of foam+ stone. Maybe worth a call. 

 

 

 

Yes I've seen that and that's what's annoying. The contractor was the "local" contractor appointed by BASF when I enquired for a Walltite quote.

 

He did say that if it was hardened lime mortar (i.e. 2 years old) then he'd chance it. The worst part is that i'm sure if you do it slowly and carefully, it would be fine, but we've got to this "computer says no" situation. I might try to ask BASF technical department directly.