Fix a crack in a wall by using a utility knife to cut the crack so it is between 1/8 and 1/4 inch deep, fill it with joint compound, embed joint tape in the compound and spread the repair material using a 6-inch putty knife. Once the repair dries, use sandpaper to smooth it with the surrounding area, but do not sand into the paper tape. Complete the repair by painting with touch-up paint that matches the surrounding wall.
Dip the tape in water to wet it before applying it over the joint compound. The wet tape is less likely to form air bubbles. Use the putty knife to press the tape into the compound and squeeze the excess out from under the edges of the tape. When applying the top coat, feather the repair to the level of the existing wall about 2 inches beyond the edges of the tape.
Wall cracks occur in plaster and wallboard as a house settles. The repair process sometimes takes a couple of days to complete, as the compound must dry. As it dries, it sometimes shrinks and requires a second coat to ensure the repair matches the existing wall. When making repairs, choose the paper joint tape, which creates a stronger and longer-lasting joint than fiberglass mesh.