Sand down the surface with 120-grit sandpaper. Create a rough surface, which will enable plaster to adhere properly.
Apply a 1/4-inch-thick layer of plaster over the surface. Use the trowel to evenly spread plaster over the surface.
Dab the broom head onto the wall in a rapid motion to create a rough texture on the surface. Work in vertical rows to cover the entire surface. Dab the broom head rapidly in horizontal rows to overlap all of the vertical rows. This will establish a complete coverage of texture on the wall.
Run the flat edge of the trowel over the plaster to create an even finish over the texture on the surface. Allow plaster to dry completely. The cure time varies greatly by brand of plaster.
Sand lightly over the entire surface with the drywall sanding block. Press gently to remove any uneven and rough surfaces while allowing the texture to remain on the wall. Paint the surface as desired.