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 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 adheres over the corner with joint compound (mud), 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 simple wallboard tape, but it can still be susceptible to damage.
The third construction method, 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 impacts.
But even this solid metal corner bead can be damaged with a heavy impact. Here's how to repair it if that happens.
Equipment / Tools
- Metal shears
- Metal file
- 4-inch, 6-inch, and 10-inch drywall taping knives
- Drywall sander
- Breathing protection
- New metal corner bead
- 1 1/2-inch drywall nails
- Drywall compound
- Fine-grit sandpaper
Mark 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.
Cut Out the Damaged Section
Using a hacksaw with a fine-toothed blade, 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.
Remove the Corner Bead
Pry out the damaged section of corner beading from the top cut to the bottom cut. Depending on how the corner bead was attached, this 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 the New Metal Bead
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.
Smooth any rough burrs off the cut edges with a metal file.
Secure the New Corner Bead
Position the new section of corner bead in place and secure it to the studs with drywall nails. 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.
Mud Over the Bead
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.
Let It Dry and Apply Another Layer
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 knife. At this point, the corner should be very close to a perfect 90 degrees.
Sand the Compound
After the final layer of drywall compound has dried, put on breathing protection and sand the repaired area with a drywall sander. Take your time and sand gently. You want to create a perfectly smooth surface for priming and painting.