Drywall cracks at seams and bullnose corners
Chrisn is correct to a point. Lumber "moves" twice a year, generally speaking, in the heating and cooling season. That's the main cause of corner beads (or tape, or nails) "popping" loose or cracking. If you are just taping over the cracks, the tape itself will eventually crack also if there is sufficient movement. Metal bead is especially prone to this sort of problem. Adding more nails in the places where it cracks the worst sometimes helps. If you have metal bead and since this is a recurring problem, it might be worth tearing it out and replacing with "mud-on" type metal-reinforced paper bead. I've had way less problems and call-backs since I started using the paper beads. Installed properly, it is bonded the entire length of the bead to the drywall rather than in a few random places by nails and what mud goes through the holes punched in the bead. Use a setting type compound to apply the bead for an extra measure of assurance.....
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