Can I apply ThistlePro PureFinish plaster on painted popcorn ceiling?

'Popcorn' ceilings are something that I come up against most weeks and have plastered over hundreds of them. Different plasterers have different methods to cover these up. However, preparation is key and you also need to consider the depth of the texture on the ceiling, how old it is, what condition it is in, does it contain asbestos? The last point being obviously very important as potentially dangerous to health. You will be very unlikely to achieve the desired finish you are looking for with the type of plaster you suggest. You would definitely need to use bonding first then two coats of multi finish plaster or if only a light texture you may get away with just two good coats of multifinsh. This can go very wrong if not competent, it's all about timing and experience, I would not advise trying it but only on the smallest of ceilings if it's your first attempt and you are determined to try.

As long as it's solid and is primed and prepared properly then yes. I personally don't guarantee over skimming artex or texture or over old flat walls because it can sometimes fail. The ideal way is to over board the ceiling, this way you won't have any problems but over skimming it is cheaper. Thanks for your question.

I agree with the above comment about boarding the ceiling as it may look sound but once you start plastering it and it becomes wet it can fail and big sections bubble and come away from the ceiling

It can be done but really is not advised. 9 times out of 10 it will distemper. May be not straight away but over a short period of time it will loose suction. Always at a minimum I would suggest over boarding. Sometimes this is found on concrete ceilings in flats etc and always advise to suspend the ceiling.