Covering a wall with wallpaper involves the use of an adhesive. Pre-pasted wallpaper is the most common type, but unpasted wallpaper was very common at one time. Unpasted wallpaper required an application of thick paste before installation. Because pasting was once the norm, some people still apply paste to modern pre-pasted wallpaper. This is a mistake, as the drywall underneath is often damaged when the wallpaper is eventually removed.
Assess the Damage
After the wallpaper is removed, the surface of the drywall may be scraped or gouged. You may see tears, in which the thin paper covering has been pulled away. Even if the wallpaper was applied to painted drywall, the adhesive can remove paint and damage the drywall. The drywall does not need to be replaced. You can repair the damage.
Remove Adhesive Residue
You may see some adhesive still stuck to the wall. Make a solution of approximately 2 pints of water to 4 tbsp. of liquid fabric softener and place it in a spray bottle. Apply the solution to the adhesive and carefully scrape the adhesive from the wall when it has softened, but only to the surface of the drywall. Do not "dig" it out or scrape away the drywall paper.
Repair the Drywall Surface
Use a utility knife or a razor to cut away loosened paper, taking care not to gouge the drywall. Fill in small holes and gouges with joint compound, smoothing the fill-in down to the surface of the drywall. If the paper removed a chunk of drywall with it, use a rotary cutting tool with a mulit-purpose bit to cut out the damaged section. Cut a new piece of drywall to fit the hole, push it in and apply joint compound around the seams of the repair. Cover the seams with drywall seam tape, run a drywall blade over the tape to smooth it and apply another coat of joint compound on top. Allow the compound to dry and sand it smooth. With the basic repairs done, vacuum the wall to remove dust and debris. Vacuum the floor as well and lay down drop cloths.
Prime and Skim the Drywall
Apply a thin coat of waterproof primer to the wall. Drywall is porous; the waterproof primer seals it, ensuring the subsequent applications of joint compound, primer and paint will not bleed into the drywall. Allow the primer to dry thoroughly before skimming the wall. Skimming is the application of a paper-thin coating of joint compound to the wall. Use a broadknife with a 10-inch or 12-inch blade. Holding the knife at an angle, skim the knife across the wall surface, smoothing on the compound in a layer no more than 1/16 inch thick. Allow the first application to dry, and apply a second coat at a 45-degree angle to the first coat.
Prepare to Paint
Sand the dry joint compound to ensure a smooth, even surface. Vacuum the walls, floor and ceiling to remove all dust and sanding debris. Apply a coat of quality paint primer to the wall and allow it to dry thoroughly. Paint the walls the color of your choice.