Bulges in drywall occur when shortcuts are taken or mistakes are made during the installation process. They may not become evident until much later. Bulges due to improper installation are often caused by overdriving fasteners or not securing the drywall to the studs properly. However, larger bulges in your drywall often occur if moisture is behind the panels due to leaking pipes or roofs.
Driving fasteners into drywall with the wrong tool, overdriving them or not holding the drywall board so that it is securely against the studs while fastening can cause damage to the drywall paper and allow the moist joint compound to damage the core of the drywall panel. This results in bulges after installation. The bulges are usually small and may occur in only a single panel. To repair this type of bulge, drill into the damaged area and remove the paper core that has swollen from the moisture. Patch the area with joint compound and allow this to dry. Sand the area smooth and repaint.
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Water leaking from your pipes can cause drywall to bulge as water pools behind it. Typically these bulges are present in ceilings, but walls may also bulge if a significant amount of water has collected behind the drywall. You may also notice discoloration such as water stains if the leak has been present for a long period. Repairing bulging drywall that is caused by a leak usually requires replacing the entire panel, but prior to that, find the source of the leak and repair the problem and then allow the area behind the drywall to dry before covering it.
Bulges that appear where two pieces of drywall meet are usually caused by the drywall pulling away from the studs behind it. You may also notice bubbling in the tape and compound applied to these seams. Loosening occurs when not enough screws are used to secure the drywall during installation, or when the drywall has not been fastened to a stud. Screws should be fastened a minimum of 12 inches apart to ensure a properly secured panel. To repair loose sheets of drywall that are bulging, refastening with more screws is often effective. However, if the panels are bent or cracked, you may have to replace them with new drywall.
Patching Bulged Drywall
If the bulges in your drywall caused by water or improper fastening are less than 8 inches in size, you may be able to repair the problem by replacing only the area that is damaged. To do this, cut a rectangular piece from a new piece of drywall and bevel the edges at a 45-degree angle. Hold this over the damaged area and trace around the new piece. Cut the damaged piece from the wall, along the outline you've made at the same beveled angle as you did your patch piece. Place the patch into the hole. If it doesn't sit flat and slightly recessed, trim the edges slightly until it does. With the patch in the wall, apply drywall tape and compound around the edges using a trowel. Do not press down too hard. Allow the compound to dry, and then sand and repaint the patched section of drywall.