Outside corners often take quite a beating, so it is a good idea to reinforce them with a metal corner bead. This is nailed to the outside corner, then joint compound is applied. Keep in mind that you should allow a day for drying for each coat of joint compound on corner joints. Pick a time to tackle this project when you won't mind having a wall "under construction" for a few days.
|Position the steel corner bead on the outside corners and use a level to adjust the bead to make sure it is plumb. When you have the bead positioned as you want it, nail it into position with wallboard nails spaced according to your local building codes.
|Use a 6- or 10-inch wallboard knife to cover the corner bead with wallboard compound. Apply three coats, letting each dry and shrink overnight before applying the next coat. Then use a wet sander to smooth the final coat.