Repair Cracks in Plasterboard

As a house settles, cracks often form at the corners of windows and door frames and on walls and ceilings. As temperatures and humidity vary, the materials in your house expand and contract. Each section tends to move at an independent rate, which can crack your ceilings and walls.

Fix simple cracks and holes using drywall joint compound and fiberglass joint tape. This involves chipping away at plaster, which can irritate your skin and get in your eyes and lungs. To protect yourself, wear safety goggles, a particle mask, work gloves, a long-sleeved shirt and long pants.

Small cracks are easy to fix. Although some people think hairline cracks add character to their homes, when the cracks reach the thickness of a spaghetti noodle, they should be repaired to protect the wall. Use a utility knife to widen the crack so the inside crevice is slightly wider than the outer edge. Then vacuum out the dust and chips. Fill the crack with drywall joint compound, using a 3-inch-wide putty knife. Flush it out so the finish is level with the rest of the wall or ceiling. Then let it dry overnight.

The next day, apply fiberglass joint tape over the sealed crack, pressing down to hold it in place. Follow with one or two coats of compound, feathering out the edges with an 8-inch-wide drywall-taping knife or a trowel to even out the finish.

Fixing small holes—those no larger than 8 inches wide—requires a few more supplies. You’ll need plaster of Paris, some wire mesh designed for plaster, and plaster bonding agent. As with cracks, undercut the edges of the hole, leaving a beveled edge that flares into the wall, rather than out. Then brush bonding agent on the lath or existing mesh, as well as along the edges of the hole.

Until recently, most plasterboard was formed by applying several coats of plaster to a backing made of strips of wood, called laths. For wood lath walls, insert a small piece of wire mesh into the hole. This creates additional crevices for the plaster to adhere to. Fasten it to the wall with drywall screws instead of nails.

Cover the hole with plaster of Paris. Smooth the mixture with a trowel, then cut off pieces of the flexible tape and seal the edges of the hole to form a frame. Finally, apply two or three thin layers of joint compound, using a trowel. Then blend the compound to match the existing finish.