Repairing a hole in a plaster wall takes a little more effort than patching damaged plasterboard. Plaster is more dense than plasterboard, and a large hole in a plaster wall is usually deeper than the width of plasterboard. The hole will expose the lath or brick -- the structure that supports the plaster. Repairing the damage takes several steps and the right tools, but you will be pleased with the results.
Clear away loose plaster and dust. Scrape the plaster around the hole with a utility or putty knife, knocking off loose pieces and making the edges appear smooth and even.
Brush a bonding agent onto the lath and the plaster around the hole. The lath is the structure that supports the plaster; the hole exposes the lath. Cut a piece of fibreglass mesh tape and press it into the bonding agent.
Mix up a patching compound according to the manufacturer's instructions. The patching compound for plaster repairs may be bought at a local hardware or home supply shop. It needs to be mixed with water until it has a dough-like substance. Only mix up the amount that you need, as it dries very quickly.
Apply the patching compound to the hole. Push the compound into the hole as well as into the mesh. Use a large blade knife to apply the compound. Smooth it out around the edges using the blade knife, as hard ridges are difficult to sand once they are dry.
Reinforce the patch with another piece of mesh tape. Press the mesh tape into the wet plaster. Allow the first coat of plaster to dry for 24 hours.
Sand the patch with 150-grit sandpaper. Sand the patch until it is even with the wall and feels smooth to the touch. Brush the dust off with a feather duster or small broom.
Make another batch of patching compound. Apply a light coat of patching compound over the first patch with the same blade knife. Allow the patched area to dry for 24 hours.
Lightly sand the patch with 150-grit sandpaper until it is smooth and even with the wall.