Interior walls are composed of plaster for durability, fire resistance and sound absorbance. However, plaster walls are not completely resistant to cracks and damages. Shrinking lumber, contracting foundations and fluctuating humidity levels are common causes of cracked plaster walls. Although cracks in plaster walls are normal, they are aesthetically unappealing and detract from a home's appearance. You need to properly repair cracks to prevent them from quickly reappearing. Fortunately, basic supplies and techniques can effectively repair cracked plaster walls.
Scrape off any loose plaster near the crack with a plastic wall scraper.
Place adhesive fibreglass mesh tape over the crack. Ensure that the tape completely covers the crack.
Mix powdered joint compound with water in a 5-gallon plastic bucket. Carefully follow the joint compound manufacturer's directions on the product's label.
Skim a thin, 1mm.-thick layer of the mixed joint compound over the mesh tape using a 4-inch putty knife. Completely cover the tape with the joint compound. Allow the compound to dry according to the manufacturer's directions.
Apply two more layers of joint compound over the previous layer. Use a 6-inch putty knife for the second layer and a 10-inch putty knife for the final layer. Extend each layer out a couple inches further than the last. Allow each layer to dry according to the manufacturer's instructions.
Sand the dried compound with 80-grit plaster sandpaper. Rub the sandpaper diagonally over the compound until the repair is completely smooth and flush with the surrounding plaster surface.
Dampen a clean cloth with water and wring out the excess liquid. Wipe the patched plaster with the damp cloth to remove sandpaper dust.
You can substitute premixed plaster joint compound for the powdered joint compound. Prime and paint the plaster wall to completely camouflage the repair.