How To Fix Outside Corners Of Plaster Walls. Rough up the areas around the repair to improve adhesion. There isn't big science behind it, but there are a few things you need to know to get a ok, so you have your corner beads fixed to the walls and you're ready to plaster.
In the past, when the paint/plaster has cracked off the metal on a wall corner, because of bumping/banging something into it, i have tried to repair it with spackle i've never seen that much damage on an outside metal corner bead.
Many older houses have plaster walls and ceilings with wood lath for a base. Moisten the existing damaged area before carefully applying plaster repair. Mix it to a firm putty consistency then use a moistened wide. How to repair cracks in plaster walls.