Ok, I have stripped for the most part two layers of wallpaper and am down to bare wall. How do I know what kind of wall I have? Drywall or plaster? In either case, there are still a few small pieces of wallpaper backing on the wall. I have successfully used DIF and have gone around and around spreading it with my fingers to remove these small places. However, in the process I have left some residual which has dried. What is the next best step to prep the walls for primer and paint? The surface is not perfect, and I am wondering if I am going to have to do more than just use a good primer. Any tips are appreciated. I have read a little about TSP, but don't know where to get it or if I should be using it as a cleaning agent prior to priming. How well will a primer hide slight imperfections in the wall?