Bubbles occur in drywall tape for two reasons: not enough drywall compound underneath the tape and gaps between the sheets of drywall. Paper drywall tape must have enough compound under it to completely cover the back of the tape but not so much that the compound creates a bulge. Sheets of drywall need to be installed as close together as possible to avoid gaps. Fixing bubbles is not difficult, and you will only use basic drywall tools.
Repairing Drywall Tape Bubbles
Use your box knife to cut a horizontal slit down the center of the bubble; cut a vertical slit across the top of the bubble and across the bottom of the bubble. This process will allow you to fold open the drywall tape.
Use your 2-inch putty knife to apply drywall compound on the backside of the bubble you cut open. Fold the tape back into place, and use your putty knife to smooth the drywall tape as flat as possible. Allow the repair to dry overnight.
Follow the process in step 1 to cut open the bubble. Use a fast drying compound to fill the gap in the drywall. Fast drying drywall compounds are not pre-mixed; you must add water yourself. Put approximately one cup of dry compound into your tray. Slowly add water, and stir until you have a consistency of at least a milkshake. You can always add more compound if you overfill it.
Use your putty knife to fill the gap with the compound that you mixed. Do not overfill the gap with compound. Your compound should be even with the surface of the drywall. Allow the compound to dry, and then follow step 2 to put the tape back in place.