Joint compound over paint?
Hello. I'm in the middle of patching some plaster walls in my home. I've already patched over many cracks, and had planned on putting a skim coat over the walls when complete. The problem is that I'm getting a large amount of bubbling in the compound. I don't think that it's my technique, and I don't think that the compound has been over-mixed. I believe that applying the compound over paint is the problem.
My question is this: is there anyway to prepare a painted wall to accept joint compound? If there is not, then is there any other type of compound that I can use?