Repairing a crushed outside corner on a wall
Why do outside corners take the damage?
An outside corner is the one place where two walls meet and stick out into the room. Furniture, vacuum cleaners, shopping bags and moving boxes all find it first. A hallway corner in a Riverside house can take a hundred small knocks over the years, and the drywall there has almost nothing protecting it except a thin strip of metal or paper-faced bead under a few coats of compound.
The damage comes in three forms. A dent is a shallow dimple where the bead is pushed in but still attached. A chip is a missing piece of compound that exposes the bead or the board edge. A crush is the serious one: the bead is bent flat, the gypsum underneath has crumbled, and the corner has lost its straight line. Each form needs a different level of repair, and picking the right one at the start saves time.
How do the three kinds of damage compare?
| Damage | What it looks like | Repair | Sessions |
|---|---|---|---|
| Dent | Small dimple, bead still straight | Fill with setting compound, two finish coats | Two |
| Chip | Compound missing, bead or board edge showing | Scrape loose material, rebuild with compound, check the bead for rust | Two to three |
| Crush | Bead bent, board crumbled, line lost | Cut out the section, replace the board and the bead, finish from scratch | Three or more |
The sessions column is about drying time, not working time. Most of the hours are spent waiting for compound to set, and a corner that is rushed almost always shows a ridge after painting.
What tells a dent from a crush?
Press a thumb into the damage. A dent feels firm underneath, because the gypsum is intact and only the surface has moved. A crush feels soft or gives way, and the bead may rattle if it is loose. Run a straightedge down the corner as well. If the bead is bent more than a quarter inch off the line, no amount of compound will hide it, and the bead has to come off.
Rust is a second warning sign. Metal bead that has been wet, or that was never coated well, leaves brown stains that bleed through paint. A stain at a corner is a signal to look at the bead itself, not just the paint, since rust expands and pushes the compound off from underneath.
How is a dent repaired?
A dent is the simplest case. Sand the area lightly to knock off any raised edges and wipe away the dust. Mix a small batch of setting compound and press it into the dimple with a four inch knife, drawing the blade along the corner rather than across it so the bead guides the edge. Leave the fill slightly proud, since compound shrinks as it hardens.
Once it has set, sand it flush with a fine sponge, then apply a thin coat of all purpose compound on each side of the corner, feathering it two or three inches out. A second coat the next day finishes the repair. Corners need a light touch because the knife rides on the bead, and pressing hard will scrape the new compound right back off.
How is a chip rebuilt?
Chips need the loose material removed first. Use a putty knife to scrape away anything that crumbles, down to solid compound or paper. Check the bead where it shows: if the metal is straight and tightly fastened, it stays, and a coat of primer on any bare steel prevents rust. If it flexes or has pulled away from the board, add a few drywall screws through the flange into the stud or the edge of the board.
Rebuilding the profile is done with setting compound in two thin passes, one side of the corner at a time. Work one face, let it harden, then do the other. Doing both sides at once leaves the knife with nothing to rest on and the corner comes out round. A sharp corner needs one edge set first as a guide for the second.
When does a crushed corner need new bead?
A crush calls for a rebuild. Mark the damaged stretch with a pencil, usually a section a foot or two long, and cut the old bead with tin snips at both ends. Pry out the damaged piece and look at the board behind it. If the gypsum has crumbled, cut it back to solid board with a utility knife and replace it with a patch of half inch board screwed to the framing.
A new piece of metal or paper-faced bead is cut to length, set against the corner and checked with a level. It is fastened with screws or nails every eight inches or so along both flanges, with the heads just below the surface. Vinyl bead and metal bead both work, though metal holds a sharper edge and takes a hit better. In a busy hallway the extra strength is worth having.
What goes on top of new bead?
Corner bead is covered in at least three coats, each one wider than the last. The first coat is setting compound pressed firmly over the flanges, with the knife riding on the bead. The second coat is all purpose compound, spread about six inches from the corner on each side. The third is a thin coat of topping compound feathered out wider still.
- First coat: setting compound, knife resting on the bead, scraped nearly clean
- Second coat: all purpose compound, wider by two inches on each side
- Third coat: topping compound, thin and feathered, sanded smooth when dry
Each coat needs to dry fully before the next. The edge of the bead itself should show only as a faint line when finished, with no metal or paper visible. A corner that still shows bead after three coats needs a fourth, as the compound shrinks and exposes it.
How should the corner be sanded and checked?
Sanding is the step where corners are won or lost. A fine sponge used with light pressure and a wrapping motion softens the edge without cutting through to the bead. Sand with the long direction of the corner, not across it. If the sponge starts to show metal, stop and add another thin coat instead.
Check the result the way any patch is checked: a flashlight held flat along the wall throws a shadow on every ridge and hollow. Run a hand down the corner as well. A good outside corner feels straight, slightly rounded at the very edge and free of bumps. Prime it before paint, because raw compound at the corner soaks up paint and leaves a dull stripe.
What can be done to keep the corner from breaking again?
Most corner damage repeats in the same spot because the cause is the same. A hallway turn that gets struck by every vacuum cleaner will keep taking hits. A strip of clear corner guard, a wall bumper or a rearranged piece of furniture takes the knocks that would otherwise land on the compound. In homes around the Mission Inn district, where older houses have narrow hallways, a bumper strip is a common fix.
Houses in the Inland Empire also expand and contract with heat. Paper-faced bead handles this movement better than rigid metal because it bonds to the compound along its whole width. A thin line of flexible caulk at the ceiling line, where the corner meets the ceiling, keeps a hairline crack from running up the edge. These small details are cheap and take little time.
How long does an outside corner repair last?
A properly rebuilt corner lasts as long as the wall itself, provided the cause of the damage is dealt with. Done in thin coats with enough drying time, the repair is stronger than the original, since the new bead is fastened to the framing instead of floating on old compound. The finished corner should be straight, smooth and ready for paint.