To finish wallboard, apply wallboard compound to all seams, nail and screw holes, and corners. Because wallboard compound shrinks as it dries, three coats are needed to compensate for shrinkage. Apply the first coat with a 4- or 6-inch taping knife and let dry thoroughly. Apply the last two coats with a 10-inch knife.
To prevent cracking, all joints must be reinforced. On outside corners, nail metal corners over the wallboard before applying compound. On inside corners and flat joints, apply a thin first layer of compound, then press strips of paper wallboard tape into the damp compound.