Repairing mold-damaged drywall is not difficult, but correcting the cause of the mold can often be challenging. Roof leaks, an improperly installed vapor barrier, leaky pipes, or constant contact with water from sinks, tubs, and showers can cause mold damage. Mold happens whenever moisture is constantly present. Mold spores attach to the paper facing of the drywall, the paper becomes a food source, and the mold colony propagates and grows. Long-term exposure to mold spores can be harmful, especially if a person is allergic to mold. You should consider consulting a mold removal specialist to determine the type of mold that is present, and you should always wear a face mask and gloves when working with mold.
Remove Mold-Damaged Drywall
Mark the damaged drywall with a pencil after you determine the area of drywall you want to remove. Use a straightedge to mark lines vertically and horizontally on the face of the drywall. Whenever possible, have the lines fall over the centers of the framing members behind the drywall; this will provide backing and a fastening surface for the drywall patch.
Confirm that there are no electrical or plumbing runs in the wall behind the marked cutout, then cut out the damaged drywall section with a keyhole saw. Wherever a cutting line intersects with a stud or a joist behind the damaged drywall, saw through the drywall at a shallower angle cutting the drywall until you reach the surface of the wood.
Cut into the vertex of corners with a razor knife. Make corner cuts wherever the section of drywall you are removing is attached to an inside corner. Cutting the corners reduces damage to adjacent walls or ceilings as you remove the damaged drywall.
Make a hole in the damaged drywall with a hammer. Grasp the drywall with your gloved fingers inside the hole, and pull the damaged drywall away from the wall. Remove the entire area of damaged drywall one piece at a time. Take your time and minimize any damage to the drywall adjacent to the section you are removing.
Remove all of the drywall from the wall if the wrong type of drywall was initially installed. On rare occasions, mold damage results from using the wrong type of drywall for a particular application. The two most common causes of mold damage, not created by water leaks, are drywall installed behind tile, or regular drywall installed in a bathroom instead of mold resistant drywall.
Remove any drywall nails or screws from the facing of the studs or framing. Often the fasteners will remain in the wood after you remove damaged drywall.
Repair the Leak
Locate and repair the source of the leak. The source of the problem is usually apparent once you remove the drywall and expose the framing. If the leak source is not easily determined, consult a licensed contractor before you replace the drywall. You must repair the cause of the leak or mold and mildew will eventually reform over the new drywall. An unresolved leak may also create additional damage to framing, insulation, siding and flooring.
Check the exposed framing for dry rot. Dry rot is a fungal infection of the wood framing members. If dry rot is present, remove and replace the affected framing. Remove and replace any wet insulation.
Clean mold off of framing members with a 1-to-8 ratio bleach and water solution. Use a scrub brush or a scrubbing pad, wear gloves, goggles and a respirator as you clean. Thoroughly dry the entire exposed area.
Paint the exposed framing with zinc oxychloride liquid, or ZOC. ZOC inhibits mold, mildew and fungi growth. Use a 2-inch disposable paintbrush to apply the ZOC, and then throw it away when you are finished. Do not try to clean and reuse the brush. Wear gloves, goggles and a respirator when working with ZOC.
Install New Drywall
Measure the length and width of the area needing drywall replacement. Use a tape measure to obtain the measurements and transfer them to the front face of a new drywall sheet. Mark lines for the necessary cuts on the drywall face using a pencil and a 4-foot straight edge.
Cut through the paper facing of the drywall sheet with a razor knife. Cut along the drawn lines. Break the drywall along the face cut, and fold the drywall slightly to make a crease in the paper backing of the drywall sheet. Cut through the crease in the backing paper with a razor knife from the backside of the drywall sheet, and remove the unwanted portion of drywall. To make cuts that are perpendicular to each other, use a keyhole saw for the shorter of the two cuts, and then fold and cut the drywall.
Position the drywall section in the opening, and use a helper to hold the new drywall in place. Install fasteners through the drywall into the wall or ceiling framing. You can use drywall nails or drywall screws. Screws are better because they cause much less damage to the internal structure of the drywall sheet during installation. Install fasteners every 9 inches on the perimeter, and every 12 inches in the field. If necessary, use a piece of plywood or one-by lumber for a backing and fastening surface behind any drywall edges that don’t fall over framing.
Tape and finish the replacement area to match the existing texture, and then paint the wall or ceiling to complete the project.