For a smooth, seam-free appearance when finishing drywall outside corners, apply a metal corner bead, and be ready to coat it with plenty of drywall mud. Follow the steps outlined below to finish drywall outside corners.
Step 1: Apply Metal Exterior Corner Bead to Outside Corner
Measure and cut metal corner bead to fit the corner. With the power drill and screws, attach the corner bead to the corner. Put in a screw for every 6 inches of vertical height, on each side, and countersink the screws. Add screws at 3-inch intervals if the corner bead is not lying flush to the drywall.
Step 2: Apply the First Coat of Drywall Mud
Use the 4-1/2 inch putty knife to apply the first coat of drywall mud, at full consistency, from the top of the wall to the floor. On later coats, you will need to thin the drywall mud with water but not the first coat. Spread it out over the corner bead, and to about 5 inches beyond the corner bead on each side. Don't cover the vertical joint of the corner bead. It gives the wall corner its sharp, 90-degree angle. Smooth over the surface with the 10-inch putty knife. The smoother each coat of drywall mud goes on, the better your final finish will look. Wait about 30 hours for the first drywall mud coat to dry. Clean your tools between each coat of drywall mud.
Step 3: Trim the Drywall Mud Coat
Skim the 10-inch knife, with its blade dry, down the drywall mud to knock off pellets. When the knife hits no high spots, apply the next coat of drywall mud.
Step 4: Second Coat of Drywall Mud
Apply drywall mud, still at full thickness, to each side, 6 inches beyond the edges of the metal corner bead. Dampen the large putty knife and smooth out the drywall mud carefully, to prevent washboard horizontal ripples. Fill in the screw heads and smooth over them. Discard any unused drywall mud and clean up your tools. Remove bumps and pellets from the mud surface after it dries with the dry blade of your large putty knife.
Step 5: Later Coats of Drywall Mud
Apply 2 more coats of drywall mud, now thinned slightly with water. Spread the next coat out to 8 inches beyond the corner support, and the last coat 10 inches to both sides. Ensure the joint of the corner bead is exposed metal after the last coat. It will be primed and painted, so it will not be visible.
Step 6: Sand the Surface
Use the 220-grit sandpaper to buff the surface. Brush and vacuum the sanded surface and check for imperfections with a trouble light. Cover any hollows or scratches with thinned drywall mud, and smooth down firmly with the small putty knife.
Step 7: Prime and Paint
Apply latex primer and latex paint, as for any drywall surface.