How to Patch Plaster Walls


Prior to using drywall in construction, homes were built using plaster and horizontal wooden slats called lath boards. The process involved a first layer of plaster pushed through the small gaps between the laths, followed by several layers of smoothed plaster. Repairing older homes with plaster wall damage can easily be done by a confident do-it-yourself homeowner and by using a drywall patch.

Things You'll Need

  • Drop cloth
  • Utility knife
  • Tape measure
  • Straight edge
  • Drywall
  • 5-in-1 painter's tool
  • Drill
  • Plastic bag
  • Primer
  • Paint
  • Paintbrush or roller
  • 1-1/4 inch drywall screws
  • Self-adhesive nylon mesh tape
  • Joint compound
  • Mud knife
  • Sandpaper (150 and 320 grit)
  • Remove all furniture, wall hangings and electrical outlet covers that may interfere with the patching process. Lay down a drop cloth to protect the floors.

  • Push a utility knife through the plaster until you hit the lath. Place your fingertip against the knife and wall. Keep your fingertip on the knife and pull it out from the plaster. Measure the distance from your finger to the end of the knife with a tape measure. This is the thickness of the drywall to use for the patch.

  • Measure the area that needs to be patched with a measuring tape. Cut out a drywall patch this size using a straight edge and utility knife.

  • Hold the drywall patch against the plaster wall and in the location where it will be installed. Score around the patch with the utility knife and then set the drywall patch aside.

  • Cut through the old plaster using the scoring line as a reference. Insert a five-in-one painter's tool into the center of the damaged area and gently work off all the old plaster from the lath boards. Keep a plastic bag handy for the pieces.

  • Position the drywall patch in place and secure it to the laths with one-and-one-quarter inch drywall screws using a drill. Cut four sections of self-adhesive mesh tape and cover the seams around the patch.

  • Apply a generous layer of joint compound over the mesh tape and over the heads of the screws with a mud knife. Make a second pass over the tape and screw heads with the mud knife to remove excess mud and leave a smooth thin layer. Run the knife over the outer edges of compound to blend it in with the rest of the wall. Wipe the knife clean of mud frequently. Let the compound dry for 24 hours.

  • Sand the seams using 150-grit sandpaper. Apply a second, wider coat of joint compound to the seams to fill in any voids. Blend the edges with the rest of the wall. Allow it to dry and then sand again with 150-grit sandpaper. Apply a final and wider coat of compound to the seams. After is it completely dry, sand the seams with 320-grit sandpaper.

  • Finish the project by priming and painting the wall using a paintbrush or roller.

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