The two major reasons calling for the repair of corner bead are cracking and damage from impact. Either way, the loose patch must be scraped away.
Cover the floor area with a drop cloth or runner and, with a 5-in-1 tool use the pointy end of the blade for digging undre the crack to seperate the bonded patch from the unbonded and uplift the seperating patch in the affected area. Normally it is easiest to enter at the crack line itself. Move along with the scraping while removing any questionable areas of lift. Remove all until you reach where the dried layers are tightly adhered.
In all probability, there will be the flange of a metal bead band, forming a crack line at the edge. Typically this is from settling. This too should be expposed fully.
Nail back or screw the corner bead to the wall. And take precautions that a corner stud is being hit for fastening.
Knife on all-purpose mudd, with a consistency that will permeate the holes in the bead, anchoring the compound.
When dry check closely to see if any cracking has occured at the bead line. Do this by lighly pressing over the surface. If any cracking recurs, it must be redone.
Reduce high spots by hand sanding (cracks often reform while under the pressure of hand sanding) and apply another layer of compound.
Build to a sufficient level, which is two coast for some appliers and three for others. Then finish sand while again, protecting the flooring.
Damage / Indentation
Metal Drywall Beads – the best remedy for damage to a metal bead is to scrape free the loosening patch and afterward remove any screws with a driver, and the nails with a cats claw. Noting that it may be difficult to remove nails without deforming the bead flange itself. One way to prevent nail pulling damage s to pry against the base of a rigid putty knife.
Vinyl Beads – for vinyl beads, chances are the disturbed patch alone can be simply removed and then apply new compound. If damage goes beyond patch and alters the the formation of the bead, the bead will have to be pulled and redone. But for minimal damage on vinyl beaded corners, and the edge has not been indented, typically patching and sanding will suffice.
After removal of the corner bead, continue scraping to remove any debris and give enough room for installation of a new bead. See how to install corner beads.
For the look of a seamless corner, complete removel of a damaged metal bead is optimal in order to recreate the outer edge. But due to the amount of labor involved in removal, the popular fix for an underlying metal bead is to remove only the damaged portion with a hacksaw, and next cut with a pair of metal snips a new piece of the same material, giving about an inch for overlap. Screw back into place overtop the severed section of bead. Then skim with compound twice (possibly three times) and sand to a final finish. Be aware however that the overlap might be visible on finished completion with this method.
Other Patching and Repair