My son has a house that was built in the early 70's. They used drywall that had a wallpaper finish rather than the typical white paper finish. In the bathroom the wallpaper has lifted and easily peeled completely exposing the gypsum. Is there a fix for this without replacing the old drywall, can I just mud over the gysum and paint? Is there anything on the market to paint over the gypsum to seal it after the wallpaper is removed? Thanks for any help.