There may come a time when a corner of your doorway or wall gets damaged. This type of repair is fairly easy to do, depending on the extent of the damage and which building material you are to repair.
Most minor to moderate repairs can be done with spackle, a self-adhesive aluminum patch, a metal putty knife(wallboard knife), an outside corner trowel, an inside corner trowel, wet/dry sand paper, and a tack cloth. If you do not have these items, you can purchase repair kits which contain all the required items you will need to repair corners, excluding the trowels.
To repair a corner which has a crack extending from the ceiling to the top of your doorway, you will need the following materials: spackle, wet/dry sand paper, a tack cloth, a putty knife, and an outside corner trowel.
The first thing you will do is sand the entire area that is cracked, including the corner. After you have sanded, you should dust off the wall with a cloth, then finish off by using your tack cloth to ensure the spackle will adhere to the wall. Take your putty knife and dip it into the spackle, spreading it over the damaged area. Push the spackle into the crack as you run your putty knife along the wall. At the corner's edge, spread spackle over both sides of the corner. Follow up by using your corner trowel to smooth over the corner edge. Allow it to dry before finishing off with sanding.
If the inside corner is damaged on drywall, the materials you will need are: wallboard compound, wallboard tape, a corner trowel, and wet/dry sand paper.
The first step is to sand the entire damaged area. Using a cloth, dust off the wall; then follow up using a tack cloth to remove any remaining dust residue. Measure out the area to be repaired, and cut the wallboard tape to the length you will need. Fold the wallboard tape in half and crease it down the middle. Next, using your wallboard knife, apply the wall board compound on both sides of the wall and into the corner. Taking the creased wallboard tape, place it onto one side of the wall. Use your putty knife to gently push the center of the wallboard tape into the corner, smoothing out the remaining wallboard tape to the opposite wall. Take your corner trowel and apply a second coat of wallboard compound over the wallboard tape and walls. Once dry, apply a third coat; follow with a wet sanding to smooth the surface.