After removing wallpaper, the wall will require some prep work before it can be painted. Not only will wallpaper paste leave behind a noticeable residue, but once the clean wall is uncovered, you may discover small blemishes, such as holes and cracks, that should be fixed before you begin painting. Once the residue is removed and any damage is repaired, you should end up with a perfectly smooth surface for your paint job.
Remove as much wallpaper paste residue as possible from the wall using a scraper tool.
Clean the entire wall with an abrasive cleaner. This will remove small bits of paste residue that the scraper missed. Let the wall dry for a full 24 hours after cleaning.
Fill in any small gaps or holes in the plaster with joint compound or with wood filler if your walls are made of wood. Brush any loose debris from the space and dampen the area with a wet sponge first, then fill in the gap and let the area set until it feels dry and firm to the touch.
For anything larger than a nail hole, first cover the hole with two pieces of mesh tape in an "X" shape, with the centre of the "X" placed directly over the hole. Cover the tape with joint compound and allow to dry.
Sand any joint compound or wood-filled spots to smooth them back down to the same level as the wall. Use gentle strokes with fine-grained sandpaper to keep the sandpaper from catching and ripping out chunks of the filler.
Continue sanding the entire wall. Sanding provides a rough surface to which paint can more easily adhere than it can to smooth surfaces.
Do not try to repair large cracks on your own. Check the width of the crack by trying to insert your finger in it. If the tip of your finger fits inside, consider calling an inspector to check your home's foundation.