Plaster and Drywall Repair

Plaster is applied wet and is forced into wood or metal lath. As it dries, the material that has oozed onto the back side of the lath forms plaster keys that hold the plaster in place. After you’ve cut the lath away to run your cable, you have to either patch in new lath for backing or use a small section of drywall for your repair. The cleaner your access holes, the easier your repairs. You might have to repaint the entire wall (maybe the rest of the room, too), depending on how much the paint has faded.
Patching a hole in drywall is a little easier than doing the same with plaster. All you need to do is …

• Even up the hole in the wall by tracing an outline an inch or so in each direction. Take these dimensions and cut out an even rectangle or square of new drywall.
• Hold the drywall patch against the wall, trace around it, and cut out an even, level hole.
• Cut a second drywall patch two inches larger in each dimension.
• Drill a hole in the center of the larger patch and pass a cord through it, knotting one end so it holds tight against the hole.
• Apply construction adhesive to the outer two inches of the face of the patch.
• Insert the patch into the wall and align it with the hole. Pull it tight to the wall with the cord.
• Tie the other end of the string to a pencil or a small piece of scrap wood, and twist it until the patch holds tight. Tape the end of the wood to the patch so it doesn’t slip. (You also can screw through the wall and secure the patch.)
• After the adhesive has set, test the smaller patch for fit and trim down the edges if necessary. Drill a hole in the middle of the patch.
• Pull the cord through the second patch, and glue the smaller patch to the larger patch, securing it by twisting the cord.
• After the patch has set, cut the string and push any excess back into the hole. Apply fiberglass drywall tape to the edges, and cover the patch with a thin application of joint compound.
• When it’s dry, lightly sand the patch with 100-grit paper and apply a second coat of joint compound, spreading it slightly beyond the tape. Sand it when dry and apply a third coat if necessary.
• Run your hand over the patch after each layer of joint compound has dried. (You don’t want to end up with a lump.)

The Finish Work

Electrical boxes must be set so they’re flush with the surrounding wall or ceiling when wood framing is used for construction (NEC Section 370-21). The gaps around the box cannot be greater than 1/8 inch; anything greater must be filled with patching plaster. The code wants to diminish the possibility of a fire spreading if a device or fixture has a short circuit. Boxes are secured by
…
➤ Nailing to the stud or joist.
➤ Plaster ears.
➤ Snap-in brackets.

Metal boxes can be used with …

➤ Nonmetallic cable.
➤ Armored cable.
➤ Metal conduit.

Nail-on plastic or nonmetallic boxes can be used with nonmetallic cable. Others are rated for use with plastic conduit.

Insulation Obstacles

Insulation is great for maintaining your house’s temperature, but it’s terrible to pull wires through, especially the blow-in cellulose type. Worse yet is solid foam. You’ll never get a cable through that stuff. If you have insulation and you’re not inclined to pull your walls apart and remove it, consider …
➤ Using some form of raceway or conduit.
➤ Installing floor receptacles.
➤ Looking for alternative locations on interior walls instead of exterior walls.
➤ Going through closets or cabinets.