The wallpaper was so old that much of the primer came off with the wallpaper (or it was never primed to begin with.) Some of the papercoating was damaged. We patched where it was damaged and to even out the surface. I'm not good at thickness - not very. To replace the drywall would be impossible. It would be the whole 2400 sq st house. Every room was wallpapered (behind the washer and dryer, behind toilet tanks you name it!). It was our plan to sand, reprime and then paint.