Michelle in Port Coquitlam, BC had a worker repair the wall and ceiling above the shower tiles. He used ordinary drywall compound and she is worried that it is going to just go soft with time.
The original wall and ceiling were made with the same material and it didn't have any problems until there was a leak from above. The reality is that this area does not receive direct water -- that's why the tiles go up as high as they do. It does need to be painted with something that will prevent any moisture penetration. That could be two coats of an oil based paint, or if you want to use the modern latex paints, start with a "vapour barrier" latex primer. With that done right, the shower humidity cannot get to the plaster to cause a problem.