Oops! Just read in my 1998 DIY Manual that you should never use gloss paint on expanded polystyrene coving - it creates a fire hazard. Can anyone tell me if this applieas to water-based gloss paint. Maybe water-based gloss wasn't available when this manual was written. I have used the water-based gloss on the paper-wrapped polysterene coving. Is there a solution if this is wrong?
check the paint tin to see if there is any reference to this type of hazard. if in any doubt the call the technical helpline (number should be on the tin) and ask them for suitability of the product.
i'd guess that water based is probably ok, it will be the solvents that react dangerously with the polystyrene - but check with the manufacturer.
as to a solution, it will be tricky to remove the paint. you won't be able to use any chemical paint strippers as this will eat the polystyrene as well (paint and polystyrene actually very similar products! both come from oil) and could constitute its own fire risk. sanding is likely to ruin the coving. might be best to remove the coving and start again.