Plaster of Paris. Most plaster contractors use various products based on the task at hand. The product shown below is ideal for casting new plaster molds to duplicate damaged crown moldings. This particular type of plaster can also be used as a finishing product, however newer and and more user friendly products are available and used more frequently. Molding plaster, when used as a finish product, can be temperamental. This is because adhesion involves each plaster layer using suction for proper bonding, and is why a barrier should be applied between coats creating extra steps. Newer plaster products work entirely different and are more sandable with better sculpting capabilities. They are also more durable and crack resistant. Most, if not all good plaster products come in powder form and are mixed just prior to using. Dry times can range from (5) to (120) minutes or better, cure times before applying primers or paint range from (4) hours to (30) days. All plaster products should be primed with an oil base product, however some water based products claim to adhere to plaster. Lakeshore still does it the old fashion way and that’s with oil. Using pre-mixed products to repair old fashion plaster is not recommended.