Scrub the ceiling to remove any dirt or grime, then let it dry.
Patch any holes in the ceiling. Prime the ceiling. On the walls along the ceiling tape 3-foot tall pieces of brown packing paper right up against the corner, using masking tape.
Cover the floor with a paint tarp. Set up the scaffolding and the platform to hold the plaster container.
Use the manufacturer's directions to find how much plaster you will need for your ceiling decoration.
Start in one corner and apply a layer of plaster to a section of ceiling; when you move to another section, make sure to blend the edges of the last section into the new section's edges. Repeat this until the entire area you want to decorate is covered. Then apply a second layer in this fashion.
Add another layer of plaster on top of the first layer of plaster. Burnish with the metal trowel. This results in a shiny surface that is marble-like.