John Hemming

It all depends whether the plaster is bad or not. if you tap the wall will your knuckle, it'll either sound solid or hollow. if it's solid, then you'll be able to patch the holes with bonding coat and skim over.
if it sounds hollow then it'll be better to take the plaster back to brick and then reboard and skim.

hope this helps.

I would recommend going over with render mesh, bonding and then skim over. this is the best outcome, rather than having to sand the ceilings down. the mesh will allow for expansion and shrinkage of the woodchip.

I would recommend having a plasterer in to sort this. you'll need to screw timbers to the back of the boards, to fix new plasterboard in the holes. then patch the holes up with multi finish.

its definitely a job for a plasterer/decorator as you'll need the patching to be perfect.

Hello.

first of all, i would always highly recommend having any asbestos removed professionally, if you do have any in your house.

the advise i'm giving is for artex ceilings without asbestos in them, but the process would be the same if you were to choose to go over asbestos artex.

you'll need to use 1 part pva and 2 parts water. some will say 3 parts water. for a good coat, i use 2.

mix together with a brush (roller can be used on flat surfaces but brush is better to get in the crevices of artex). brush over the whole ceiling.

once it's dry or tacky to touch, apply a thick coat of multi finish plaster. then flatten the ceiling so there's no lines.
once the ceiling is damp to touch, but not leave any finger prints.. this is the time to apply the 2nd coat of multi finish plaster.

once this is on, i use my refina flexi trowel to flatten the ceiling and finish it. usually takes around 4 trowels overall.