A drywall-covered wall that has visible joints can destroy the appearance of an entire room. Drywall finishers coat joints with tape and thin layers of joint compound to blend them into the wall. When they use insufficient joint compound, however, the joints can appear as ridges, or the tape can separate. Defects, including cracks, can also appear if the wall gets wet or if the framing moves. To hide defective drywall joints, you usually have to recoat them while removing and replacing tape that has bubbled or separated.
Cut out bubbles in drywall tape with a utility knife. Slice off all the loose tape, leaving only that which is firmly attached to the wall. Scrape off loose and chipping joint compound from around the bubble with a 6-inch drywall knife.
Spread a coat of drywall primer over any joint you are going to repair. Joint compound and tape adhere better to primer than they do to wall paint. If extensive repairs are needed on the wall, paint the whole wall with primer.
Lay new drywall tape over any areas from which you removed tape. Spread all-purpose joint compound on the area with a 6-inch drywall knife and lay the tape on top of it, making sure there are no voids under the tape. Scrape over the tape with the blade to flatten it.
Lay a coat of joint compound over the entire joint you are repairing, including areas you’ve retaped, with a 6-inch knife. Scrape it flat and let it dry overnight.
Spread a second coat of joint compound over each joint with an 8- or 10-inch knife. The wider knife allows you to feather the edges of the repair farther from the center of the joint, thus creating a wider, flatter seam. After the joint compound dries, repeat the process with a 12-inch knife.
Sand the final coat with 120-grit sandpaper. Shine a work light obliquely on the wall while you’re working to help you spot ridges and uneven spots so that you can sand them down. Wear a dust mask, because sanding raises a large amount of dust.
Prime the joint compound with drywall primer before you paint it.