Skim coating a ceiling can be done over a small portion for repairs, or over the entire ceiling. A thin layer of plaster is applied to the ceiling, leaving a smooth surface. Occasionally, several layers are required to create an extremely smooth surface. Remember to use extra safety measures when working overhead to avoid accidental falls.
Wear safety goggles to protect your eyes and a safety mask to avoid inhaling dust. Place a bandanna or hat on your head to prevent plaster and dust from falling into your hair.
Ensure the surface is as smooth as possible. Use a putty knife or trowel to remove all loose paint or texture. Sand the ceiling with fine- to medium-grit sandpaper. Wipe the area with a wet cloth to remove all plaster dust. Allow the ceiling to dry.
Dip a putty knife or trowel into ready-mixed wet drywall joint compound. Smooth the plaster on in a thin layer—similar to buttering toast or icing a cake. Clean the trowel after each stroke of plaster by wiping on the lid of the joint compound bucket. For extreme plaster build-up, wash the trowel in water and wipe it with a damp cloth. Use all vertical or all horizontal strokes. The plaster should not be thicker than 1/4 inch. Allow the plaster to dry.
Sand the newly applied plaster with medium sandpaper—inspect it to see if the area is smooth. Remove any ridges created when trowelling by scraping raised areas with the trowel. Add additional layers of wet plaster and repeat the process until the ceiling skim coat is as smooth as possible. Work in vertical strokes if the first layer was applied with horizontal strokes and vice-versa. Continue to alternate stroke direction for each layer.
Apply the plaster above your shoulder area—never directly above your head--to ensure balance while working on a ceiling.