Without going into too much of the sordid details, part of my kitchen ceiling is down and I want to plaster it and then repaint it. The area is about six by eight feet squared. I started using basic Plaster of Paris, but it's very difficult to work with -- it dries too quickly and then the sanding is rediculous. So someone suggested I use pre-mixed compoud and mix some plaster in with it. I tried this, but he had instructed me to mix way to much plaster in with it -- the whole mess dried within about 1/2 an hour and was much too thick to work with properly. So I'm wondering if there is a formula to use when mixing plaster in with compound for this purpose. Any suggestions would be much appreciated.