Painting plaster walls usually involves a little more preparation than is required for painting other types of surfaces. Most home owners and do-it-yourselfers, however, should be able to get the job done with little or no major problems. Some repairs may be necessary before painting plaster, depending on the condition of the wall. After this is done, many home improvement experts suggest that the wall then be sanded, cleaned, and primed.
Repairing cracks and holes is the first step towards painting plaster walls. While fine, hair-line cracks may be filled in by a couple coats of paint, larger cracks and holes will need extra attention. Smaller cracks and holes are usually a simple fix, and require nothing more than being filled in with joint compound.
Larger blemishes generally require a little more work. Before beginning, any bits of loose plaster need to be removed and scraped away from the hole. Most of the time, the resulting hole is larger than the original. Work plaster or joint compound into the hole, squeezing it in between the strips of wood behind the plaster. The freshly applied layer of joint compound should come just below the surface of the original plaster, and it should be scored with a nail or other sharp object to help the top coat stick.
After the first layer is completely dry, the second layer can be applied. This top layer should be scraped smooth with a wide putty knife and be flush with the wall. To finish the repair, the edges of the patch should extend beyond the edges of the hole. Any repairs need to be allowed to dry completely, as wet, new plaster will not hold paint.
Before painting plaster walls, many times the walls will need to be sanded, especially if there were repairs. Edges of repairs should be sanded to make them somewhat smooth. Smooth plaster should be sanded just enough to allow the paint to stick, and rough plaster walls, such as textured plaster, should be sanded down until they are smooth.
Because they hold more moisture, plaster walls tend to attract more dust from the air, and often get dirtier than most other walls. Cleaning the wall is considered to be an important step before painting plaster. This removes any dust that could leave a gritty feeling and spots in the fresh paint.
To clean the walls, many people use a soft bristle brush to remove any fine particles from them. Afterward, the walls can be wiped down with a slightly damp cloth. If there are stains on the wall, some experts recommend using a mild solution of trisodium phosphate, which can be purchased at most home improvement stores. Before priming or painting plaster, it should be allowed to dry completely.
Because plaster is so absorbent, a good primer may be necessary before painting plaster walls. This will help prevent any stains on the plaster from bleeding through, and flaking off the paint later on. Stain-blocking primer for plaster is considered the best, and one to two coats should be enough.