As above thinking of using it as a buck/mould for some fibreglassing i know polyurethane is ok with resins, not sure if the celotex is the same?

It does look like the right stuff that i saw in wickes!

resin normally gives off styrene gas, so any foam with the word styrene in it will disolve very quickly.
Even non styrene foam doesn't really like resin.
But if you shape it, then cover fully with body filler, then resin on top of that its fine.

Certainly florists oasis foam is okay with it. Not sure what celotex is though! Certainly the same crumbly texture of oasis.

I guess i could buy some and do a test piece with some gelcoat

i'll see if i can find some of that florist oasis foam stuff

to the best of my knowledge celotex is a polyurethane foam and is ok with normal polyester resins. I would still do a test bit first. there are similar thermal boards that are phenolic based, they start dark yellow / orange and go brown in sunlight.

hth

Cheers all

I have used polyester resin over celoex and the only problem I have noticed that if the resin gets warm during curing it can create bubbles if any air is not rollered out. This happened during the last cold winter so may be due to the extreme temperatures we experienced.

Cellotex is pretty dear stuff so you might be best off keeping your eyes open going past builders at work and see if they have got any offcuts you could have to try out first. I have quite a few bits in the skip on our job, just a bit too far away for you! Also try a proper builders merchants rather than a diy chain as they will be cheaper.

The wickes stuff is 1200mm by 450mm 50mm and for a fiver isn't to bad tbh, i should only need two for the half doors i might make!

now i've been looking at the carbonmods kits to make carbon parts from a mould.... noooo it would be way to expensive stop looking!!