How to Do Corner Beading on Windows

Cut a strip of corner beading to the length of the corner. Avoid piecing the beading together along the corner. Place it over the raw corner edge. Screw it in place along both sides of the corner every 6 inches. Be sure the screw heads lie slightly below the surface of the beading, but do not screw them so tightly that they dent the beading. Run the blade of a drywall joint knife down each side of the corner to ensure it is smooth.

Mix drywall compound, also called mud, with water according to label directions. Scoop up a generous amount of mud with a 4-1/2-inch joint knife. Start at the top of the corner on one side and hold the knife at a low angle to the drywall. Pull the knife downward, spreading the mud 4 to 5 inches in from the corner and covering the holes in the beading and the screw heads. Feather the mud away from the corner. Use more mud as needed, and make the side of the corner as smooth as possible. Scrape excess mud from the area, but do so lightly and form the corner into a smooth, slightly rounded point.

Repeat Step 2 to cover the other side of the beading. Let the mud dry completely, about 24 hours. Meanwhile, clean your knife and other equipment that came into contact with the mud. Do not let it dry on any of your tools.

Run the flat edge of your drywall joint knife down one side and then the other of the dried corner. Do not gouge the dried mud, but use enough pressure to knock off any ridges or high spots. When the surfaces are even and the mud blends smoothly into the drywall on both sides, apply another coat of mud to the corner that extends about 6 inches onto the wall on both sides.

Wet the edge of a 10-inch joint knife and smooth out the wet mud on both sides of the corner. Again, feather it away from the corner. Spend as much time as you need to even out high or low spots. Let this mud dry. Remember to clean your tools.

Even out the dried mud with the 10-inch knife. Spread another coat of mud on the corner with the 10-inch knife, this time extending it 8 inches onto the wall on both sides. Even it out with the wet edge of your knife, and let it dry.

Build up another coat of mud extending 9 or so inches onto the drywall this time. Follow the same technique for evening out the surface, letting it dry and knocking off high points after it has dried.

Fill in any small gouges or ridges with mud that is thinned with more water. Let it dry. Lightly sand the surface with 220-grit sandpaper. Do not sand any more than you have to. Remove the dust with tack cloth. Now the corner bead is ready for priming and painting.