I just had at some offcuts of the PIR insulation board that my house is full of with a blowtorch. Sadly, I didn't install it, so I don't really know what it is, other than "inadequate".
It's got foil on one side and white plastic on the other and it's about
25mm thick.The good news is it won't burn by itself and doesn't burn that well with the blowtorch on it. As soon as you take the heat away, it goes out. Even under the torch it chars and crackles, but is very reluctant to burn.
That's my experience of trying the same.
The canned foam however, often used to close gaps in celotex, can vary from similar (esp red "Fire foam") to "bloody hell" in some other cases.
When I firestopped the ceiling of the integral garage in my last house, I was alarmed to see that the foam was marked "Highly Inflammable" even though it was firestop foam. I assume that's the propellant.
Not my problem, now!
Which ends up where in a closed-cell foam?
The acoustic mastic I used for sealing around my "noisy neighbour wall" can also be used as intumescent firestopping, it was frame-gun applied rather than a foam.
Well, quite.
I only used the foam where cables penetrated the ceiling. Everywhere else I used intumescent (tee-hee) mastic.
Yes, I was amazed how fiercely "normal" foam burns. I had a lump platerboard fixing foam in the garage left over from cleaning the gun, and I thought I'd turn the blowtorch on it just to see. It really went up - literally roaring. I'm not sure if there is any low expansion fire foam that is sticky enough to hold up plasterboards. Makes you realise how important is the mechanical fixing at the top of the platerboard ... Simon.
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