The first step is to scoop the joint compound onto the masonite.
Next, I use a plaster tool to smooth a thin coating of plaster over the surface of the masonite. I strive for a layer that is 1/16" to 1/8" thick. I used to tell people that it is like frosting a cake, but I really have no idea if that's true!Now I must wait for about 48 to 72 hours so that the plaster is hardened and dry. I will sand the surface to smooth any sharp edges. Next I will paint two coatings of gloss polymer medium to make the plaster waterproof. That is necessary because I use watered acrylic paints to make my color layers.