Installing plaster is a four-step process. 1. The first step is to install the lath. Lath is a wooden or metal grid that's nailed to the wall and provides a surface for the plaster to stick to. 2. The second step is to apply a coat of mortar to the lath. Mortar is a mixture of sand, lime, and water that serves as the adhesive for the plaster. 3. The third step is to apply the plaster itself. Plaster can be applied in one or more coats, depending on how thick you want it to be. 4. The fourth and final step is to sand and polish the plaster finish.