Screenings also known as stone dust is a very durable sandy like material that is great for the final grade for all types of stonework. Typically used to level out areas before laying pavers or flagstone some people even use it for the final grade on driveways. It provides a solid clean surface that compacts and looks like concrete making it another affordable alternative for driveways and patios. Screenings is the finest of the types of crushed stone. Although it is made from the same type of stone as the other two types, it is crushed into a powder. When used by itself screenings forms a hard surface that is water resistant. Since screenings can form a strong, porous surface, it not only protects the base of the area from moisture, it also keeps weeds and grass from growing up between the pavers. Screenings provides an efficient final base layer and these aspects are what make it a great material to go under patios.