I used paper inside and outside corner beads and some of them are cracking. Is there anything I can do to fix them, or do I have to replace them?
Corner bead is generally a metal bead on the outside corner of your drywall. That it is "cracking" indicates that it was not done correctly in the first place.
Tear off whatever is there and do it right with metal corner bead installed with 1 1/4" drywall screws and then drywall compound to finish.
Only inside corners are done with paper tape.
Also, make sure that nothing is moving and that all the seams are supported.
The tape that you used is failing because it did not bond with the drywall compound under neath. It needs to be imbedded into wet compound for it to stick. If its just a few spots, use a sharp utility knife to cut out the spots that are lifting, then cover the hole with compound. If it's a lot of places of sections or more than a couple inches long. You're going to have to remove the whole corner and start again.
We use a combination of outside corner beads of paper and steel on the back side. Just using paper is not the way to go. You have no strength on the corner itself. The best way to do inside corners is buy perf a tape. It comes in rolls of 250 or 500 ft rolls. It creases in the centre of the roll so it will fit a 90% corner. Make sure you put lots of mud under the tape of you will get bubbles meaning not enough mud under the tape to bond it properly to the drywall. It's alot easier to replace than fix because I don't think you have the right beads to start with.
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