If the interior walls of your home are surfaced with drywall, chances are at least one exterior corner has been crippled by a vacuum cleaner, couch, or runaway Radio Flyer wagon. A coat of spackle and paint won't hide the resulting cracks and disfiguring dents. The only solution is to cut out the damaged corner and rebuild it with a new metal corner bead and fresh joint compound.
The actual repair takes only a couple of hours, but you will have to wait overnight for the joint compound to dry before applying the final paint coat.
Step 1 - Uncover Old Metal Bead
Start by using the utility knife to make a vertical slice on each side of the damaged metal corner bead (photo 1). Position each cut about two inches away from the corner and make both of them long enough to encompass any hairline cracks visible above or below the point of impact. With the repair area outlined, use the hammer and cold chisel to chip off the old joint compound and expose the metal corner bead beneath.
Step 2 - Cut Out Damaged Section
Use the hacksaw to cut through the bead (photo 2); remove a section at least six inches long around the damage. If the bead is screwed in place, remove the screws and pull it out with pliers. If it's nailed, gently pry it off without crushing surrounding surfaces. If you can't pry out the nails without further damaging the wall, use the snips to cut the bead from around the nailheads. Then pull off the damaged section and tap the nails below the surface with the hammer.
Step 3 - Measure and Cut a New Metal Bead Section
Use the snips to cut a new piece of bead to fit into the space where the old section was removed. A tight fit is important, so measure carefully to make sure the new piece doesn't overlap the existing one.
To snip through the L-shaped bead, cut in from each edge, then bend the piece back and forth until it breaks off. Metal corner bead is sold in eight-foot lengths that cost about two dollars each.
Step 4 - Attach New Bead Section
You can attach the new bead section with 1 5/8-inch drywall screws or two-inch drywall nails. Nailheads lie flatter and are easier to spackle over, though hammering them in can crack the old joint compound. Screws hold better, but their thicker heads are a little harder to conceal, especially if the existing corner bead is covered by a thin coat of joint compound. Our corner was finished with a thick layer, so we fastened the new piece with 1 5/8-inch-long drywall screws (photo 3).
Be sure the new bead's edges align with the existing corner. If you've secured the patch and the edges are misaligned, try tapping them straight with a hammer. If that doesn't work, you'll have to remove the replacement piece and put in a new one.
Step 5 - Apply a Thick Coat of Joint Compound
Once the new section of corner bead is securely fastened, the next step is to cover it up with joint compound. Thoroughly stir the material until it's smooth and lump-free. Then use the four-inch drywall knife to spread compound over both sides of the corner (photo 4). Don't fuss over this first, thick coat of compound—it will shrink, and you'll need to apply at least two more thinner coats. Just lay it on and wipe it smooth.
Step 6 - Add More Compound and Paint Over It
Wait for the first coat to dry (10 to 12 hours). Then, use a sanding block and 80-grit sandpaper to knock down the high spots (photo 5). Switch to the eight-inch drywall knife and spread on a thinner, wider coat of joint compound with more care. Apply pressure on the outer edge of the knife as you draw the tool across the surface to form a thin, "feather edge" of compound. After the second coat dries (about two hours) lightly sand it with 120-grit sandpaper. If needed, apply a thin skim coat of compound to fill airholes, scratches, and other flaws. Wait two more hours or so, then wipe down the repair with a damp sponge and apply two coats of paint.
Courtesy of American Tool