On most walls constructed with drywall, the pristine edge formed on an outside corner is the product of a hidden strip of metal corner beading that runs the length of the wall from ceiling to floor. Because it is hidden beneath drywall compound and paint, you don't even know it's there. It is present to protect that corner from small impacts, and it does this job very well. But a heavy impact, such as might happen when you are moving a large piece of furniture, can bend or even tear away that metal corner bead, leaving you with a badly damaged wall corner.
Drywall Corner Construction
There are three ways that outside corners are constructed with drywall. First, ordinary paper or fiberglass seam tape can be wrapped around the outside corner and mudded over. But it is hard to form perfect corners with this method, and such corners are very susceptible to damage.
Second, there is a type of corner bead that includes two paper flanges attached to a thin L-shaped strip of metal. This type of corner bead is adhered over the corner with taping compound, then is finished by applying an additional layer of mud over the corner bead and sanding it smooth. This type of corner bead represents a better corner treatment than simply wallboard tape, but it can still be susceptible to damage.
The third construction method, and the method that most professional drywall crews use is to cover the corner with a full-metal corner bead that is attached to the studs with drywall nails or screws. The bead is then covered over with drywall compound and sanded smooth. Because this is a nailed-in-place bead, such corners are quite durable and resist most routine impact.
But even this solid metal corner bead can be damaged with a heavy impact, and you may well be faced with trying to replace a damaged section.
Tools and Materials You'll Need
Cutting out and repairing a section of metal corner beading usually takes about 30 minutes, and requires the following materials:
- New metal corner bead
- Metal shears
- 1 1/2-inch drywall nails
- Metal file
- Drywall compound
- 4-inch, 6-inch, and 10-inch drywall taping knives
- Drywall sander and fine sandpaper
How to Repair a Damaged Corner Bead
Work slowly and carefully when removing a section of damaged corner beading. It can be hard to blend in a new section if you damage the edges of the existing bead when you cut out the damaged section.
- Mark the section of the corner where you want to replace the corner bead. It's best to mark a few inches beyond the damaged section in both directions.
- Using a hacksaw, carefully saw horizontally into the wall across the corner at both the top and bottom of the marked cutout area. The cuts will slightly damage the surrounding wall, but this is easily repaired later. You should be able to feel when the hacksaw has fully cut through the underlying metal bead strip.
- Pry out the damaged section of corner beading from the top cut to the bottom cut. Depending on how the corner bead was attached, they may involve removing drywall screws or prying out drywall nails that were used to hold the metal bead in place. This is a slightly messy job, but any damage will be repaired later.
- Cut a section of new metal corner bead to exactly fit the gap you removed. Hold the metal bead steady while cutting, because you want to avoid bending the flanges. You may find this easiest if you use metal shears rather than a hacksaw to cut the bead.
- If necessary, smooth any rough burrs off the cut edges with a metal file.
- Position the new section of corner bead in place and secure it to studs with drywall nails. (Nails tend to work better than drywall screws in this application, since the heads of the drywall screws may extend out too far and interfere with mudding.) Use care when nailing not to strike the vertical edge of the bead and bend it.
- If the ends of the existing corner bead were loosened when you cut out the damaged section, also nail down the flanges on the existing corner bead extending above and below the repair section. Your goal is to create a smooth vertical line from the old bead to the new bead that can be smoothly mudded over.
- Trowel on a layer of drywall compound (mud) on both faces of the corner, using a 4-inch drywall knife. One edge of the knife should glide along the metal bead as you apply it. Don't be concerned about making a perfect 90-degree angle at this point.
- Allow the compound to dry, then apply a second coat of compound to both faces of the corner using a 6-inch drywall knife. Allow this layer to dry.
- If necessary, a third coat of compound can be applied, using a 10-inch wallboard knife. At this point, the corner should be very close to a perfect 90 degrees.
- After the final layer of drywall compound has dried, sand it with a drywall sander to create a perfectly smooth surface for priming and painting.