Painting - Painting over plaster

The ceilings in my girlfriend's house don't seem to hold paint. They are horse hair plaster ceilings and the paint becomes chalky all over and flakes in some areas. The previous owner told her it was because either the plaster or the paint (she can't remember which) has calcified. I don't have a clue on how to help. Any ideas on how to get a fresh coat of paint to last would be greatly appreciated. (Would really score some brownie points with her if it works!!)

it has been awhile, but if i remember correctly there is a product called 'wall size'. it is used to seal plaster before wallpaper adhesive is applied. it blocks the plaster from absorbing the liquid in the adhesive. check with your local wallpaper and/or paint store for such a product, they could be real helpful with your problem.
good luck

I'd use an oil primer and oil ceiling flat for added security. Whenever water enters plaster (ie latex paints), the lime content of the plaster can react and gives off carbon dioxide which can manifest itself as bubbling, lifting paint etc...the older and drier the plaster is, the more likely this is to occur. It may not always happen, but if it does, a decent sanding to clean the are up, a good alkyd or oil primer will keep latex from penetrating back into the plaster. You could use latex on top of the oil primer also, or even use the oil primer as your finish coat if it looked good enough to her but ceiling paints are a much nicer white. Hope this gives you some options to consider when repainting older plaster homes. :)