To repair a popcorn ceiling, saturate the damaged area with hot water, remove the damaged texture with a putty knife, and apply joint compound and drywall mesh to the area. Sand the joint compound with fine-grit sandpaper after it dries, and apply canned popcorn ceiling texture to the area.
To prepare the area, apply one layer of joint compound, place a piece of mesh drywall on the compound, place a second layer of joint compound over the mesh, and allow the compound to dry. If necessary, apply a small amount of joint compound to fill depressions in the mesh, and allow the compound to dry before wiping the area with a cloth to remove dust.
Follow the manufacturer's instructions to apply the popcorn ceiling texture properly, and blend the texture into the surrounding area at the edges of the patch by applying a small amount of the texture to the adjacent areas of the ceiling. Apply primer to the refinished area before painting to match the surrounding area.
To repair a small crack in the ceiling, remove 2 inches of texture on each side of the cracked area, and apply a bead of caulk down the center of the area. Smooth the caulk with a fingertip, allow the caulk to dry, and spray the popcorn ceiling texture onto the area.