Kingspan bathroom ceiling cover

Can't understand this post. You plan on having a foil ceiling, with the words 'celotex insulation products', all over it in your bathroom? What are you trying to acheive?

If your bathroom ceiling is going black with condensation. why not just use insulation-backed plasterboard? - or insulate the loft above the bathroom so that the ceiling isn't so cold.

It's foiled both sides, but as PhilL says - use kingspan backed plasterboard.

I've got lots of kingspan from the kingspan depot at kingsland, so I'm using that. If I glue plasterboard under it could it crumble with damp? [g]

You might find it entertaining to achieve a long term bond to the foil surface :-) Why not screw through both plasterboard and kingspan into the joists before skimming?

Skimming is a skilled job, another reason for not using plasterboard, but something damp-proof and easier? [g]

If you don't want to skim, then just screw PB to the ceiling (through the foam) and fill any holes and gaps with board fill. Give it a quick sand when done, and then a couple of coats of emulsion.