Holes in plaster, from small cracks to openings large enough to put your hand through are usually repaired with spackling compound. This comes in powder form and is mixed with water as needed to make a smooth paste. The ratio of powder to water is not critical. The paste must be smooth but stiff enough to remain where it is spread without running, and soft enough to spread easily. Spackling compound in paste form, that is, already mixed, is also available.
Before applying the spackling paste to the job, wet the plaster around the hold or on both sides of the crack with a sponge or damp cloth. Plaster tends to absorb moisture, and if the spackling compound is placed on dry plaster, the moisture from the compound will be drawn out too rapidly to make a good bond.
For small holes or hairline cracks, just apply the spackling compound to the spot to be filled with a large putty knife. Use only a little more compound than is necessary to fill the opening, and smooth it to a featheredge, removing any excess with the putty knife. For larger openings, first scrape away any loose plaster in the crack. Use a screwdriver, beer can opener, or any pointed tool to do this. To make a good bond, it is generally supposed that the crack should be wider inside the wall that at the surface. However, ideally the crack should be undercut on both sides. Practically, it doesn’t make too much difference. Open the crack wide enough to clean out all loose plaster, and then apply the spackle. If enough to clean out all loose plaster, and then apply the spackle. If the opening is large, allow a first coat to dry and then apply a second. When the job is finished, the wall can be covered with paint, wallpaper, or whatever you wish.
If there is a lot of loose plaster, chisel away edges that arouse the least suspicion of fault. If you cut away too much, you can patch up the hole, but if you leave some crumbly plaster, the whole job will be spoiled later.
When a large opening is to be plastered over, as when an electric fixture is removed, you will have to furnish a base for the spackling compound. One-way to do this is to cut a piece of plasterboard to fit. When it is in place, the plasterboard should be about 1/8 inch layer of spackling compound to finish the job. If you do not have any plasterboard or similar material, you can do an adequate job by stuffing the hold with newspaper crammed in about a 1/8 of an inch below the plaster surface. Then finish with spackling compound as before.
