I have plaster walls in my stairwell that have 2 layers of very old wallpaper. After removing 3 layers of wallpaper from a bedroom walls and ceiling, I was told about "skincoating" drywall over the wallpaper to get a new looking wall. It seems to be working but can be trying. Is there a trick to doing this? I like the results but wonder if I am doing something wrong. I have a difficult time getting it to go on as thin as I would like.