It might be the gas fire.
As I remember, unburned Calor gas decomposes to carbon dioxide and water when exposed to air. I believe there's some water after burning too.
Have you got an electric heater you could try instead?
Thanks for that - sounds like it could be it. I don't have an electric fire that would get it up to a sensible working temperature that quickly, so I guess it's back to the wood burning stove. I am only burning off cuts and sawdust in it, so nothing should
produce any significant moisture.
What I can't understand though is why only the sides wrinkled, and immediately on spraying.
The only other info is that Rustins say that the stuff goes thru a phase after about
12 to 14 hours where it is prone to wrinkling. I can't have left it for more than 3 hours in a temperature of about 75F. Even if their data is miles out, that wouldn't explain why it only happened on the sides.
I have sanded the sides back as best I can, and I'll leave it to go off till Monday, then have another go without using the gas fire. I'll also try bringing it back in the house to dry. Praying might be in order as well!!