Before putting primer on rough-textured paint or washable wallpaper, they must either be stripped first, or lined with a special paper after they are primed.

If the walls are smooth and painted, paneled or covered with tightly adhering washable wallpaper, wash them with a strong detergent containing ammonia.

The most difficult wallpapers to remove are the nonstrippable types that resist moisture penetration - some are coated with vinyl and referred to as washable wallpapers, and others are made with woven fabric or foils - and wallpapers of any kind that have been covered with paint.