How To Repair Interior Cement Plaster

Originally Posted by mjay

It's so much easier to google, cut and paste.
Below is the basic outline. In Britain we add a little PVA [white wood glue works] to the water to brush onto the scratch coat [the texture finish you mention] this seals the surface in prep' for your finish coat. I prefer "hot mud" for repairs to plaster.

Plaster washers:
You can take the sag out of your plaster ceiling using these little gadgets. First, using an old chisel or putty knife, remove any loose or crumbling plaster in the area that is to be repaired. Slightly undercut the edges of the existing plaster to create a solid bond with the new plaster. Use a vacuum with an upholstery attachment and an old paint brush to remove dust and surface debris.

Next, insert a galvanized drywall screw (1-5/8 inches to 2 inches) through the center hole of the plaster washer, and place the screw head into a number-2 bit on a screw gun. Drive the screw through the plaster and into the wood lath a couple inches back from the edge of the hole or crack that is to be repaired. Tighten down the drywall screw just enough to pull the sagging plaster up against the lath, and flatten out the convex-shaped washer. If the plaster does not pull up and-or the screw does not tighten up, you have likely missed the lath and should back out the screw and move it slightly in one direction or the other.

Keep in mind that there is a slight space between each strip of lath. Install several plaster washers around the area to be repaired. If there is evidence that the lath is not securely fastened to the framing, use longer drywall screws in combination with the plaster washer and drive the screws through the plaster and lath and into the framing.

Once the plaster has been resecured to the lath, using a 6-inch taping knife, apply a plaster patching compound to fill in the hole or crack. Before applying the patch material, spray the lath and existing plaster with water. This will prevent moisture from being sucked out of the new patch material, which could result in cracking and a poor bond. Allow the patch to dry and then sand it level.

Conceal the plaster patch and the plaster washers by covering them with a self-adhesive fiberglass mesh joint tape. Use the 6-inch taping knife to apply a thin coat of drywall joint compound over the patch area. Feather the joint compound at the edges of the patch. Allow the joint compound to dry overnight and apply a second coat overlapping the first coat by a couple of inches in all directions. Allow the material to again dry overnight, and lightly sand using 100-grit sandpaper or sanding mesh along with a sanding pad or block. Additional coats of joint compound and sanding might be required to achieve the desired finish.

After the final sanding, use a damp rag and-or a tack cloth to clean the patch area and prepare it for painting. Prime the patch with a high-quality interior acrylic latex primer and when it's dry apply one or two coats of paint to match the existing finish.


Hope that helps.

p.s. Pre-drill the holes, the lathe is very dry and will split easily. Use fibreglass tape on all cracks.