To create smooth, round or sharp corners on a drywall edge a corner bead is installed where the edges of drywall are joined at the corner. Under the joint compound on the corner is a metal or plastic bullnose corner bead which is a strip of metal that creates the shape of the corner. To repair a chip in the plaster on the edge of a corner you must scrape off the old plaster or joint compound to the bullnose corner strip, repair the bent bead nose and replace the plaster or joint compound.
Scrape away a few inches of the old drywall from both sides of the chip to expose the corner bead underneath using a 1 ½ inch drywall taping knife. Peel away the drywall and use a drywall taping knife in an up and down motion to scrape away any loose drywall to make the edges of the repair area clean and smooth. Gently tap the metal corner bead until it is straight with a sharp edge using a hammer. Make sure to uncover the entire damaged parts of the corner bead.
Tighten any existing drywall screws that appear loose in the corner bead. Reinforce the corner bead by adding additional drywall screws with a drill.
Use a mud pan to mix the 45 minute drywall mud with water following the instructions on the label. Mix only as much as you need to make the repair.
Apply drywall mud to the repair area from the nose of the bead moving toward the wall using a six-inch drywall taping knife. Apply mud until it is level with the existing wall. Allow enough time for the mud dry thoroughly. Scrape the first layer of dry mud in an up and down motion to form a sharp corner using a six-inch taping knife. Apply a second coat of mud with up and down strokes keeping the corner sharp and straight. Let the layer dry thoroughly. If your wall is not textured, sand the patch with 120 grit sandpaper to smooth and blend the patch with the wall surface.
Blend the edges of the patch with the textured wall surface using a wet cloth to feather the edges. Use the wet cloth method if your walls are textured. Let the mud dry thoroughly and texture the wall to match the old wall before priming and painting.
Cover the floor under the repair area with plastic to protect it from damage. Keep kids and pet away from the area.
Wear safety glasses to protect your eyes while scraping drywall or mixing mud.