To paint over wallpaper, replace damaged pieces of wallpaper, and apply adhesive to any wallpaper that is loose. Apply a thin bead of clear caulk around the top and bottom of the wall where the wallpaper meets the ceiling and floor, and spread a thin layer of joint compound over the wallpaper if it is heavily textured. Apply oil-based primer to the wall, followed by one to two coats of oil-based paint.
Allow the caulking and joint compound to dry before applying the primer, and allow the primer to dry before painting the walls. Another method to paint wallpaper is to clean the wall with a solution of 1/2 cup trisodium phosphate mixed into 2 gallons of water. Ventilate the room while cleaning the wallpaper, and wear protective gear.
Use a damp sponge to remove the trisodium phosphate after cleaning the walls, but do not saturate the wallpaper. When the wallpaper is dry, apply an oil-based primer-sealer to the wall, followed by one to two coats of oil-based paint.
Allow the primer and paint to completely dry between coats, and apply a topcoat after the paint dries. If the wallpaper is peeling or otherwise damaged, remove it before painting the wall, as painting can cause further damage to the wallpaper.