a mixture of sand, clay, and highly refractory materials, such as chamotte and asbestos, together with a binder, used for making single-casting and semipermanent molds.

Both natural and synthetic molding sands are used. Different molding sands are used for the casting of pig iron, steel, and nonferrous metals. Molding sands may also be classified as facing sands, black, or floor, sands (for backing and filling), and all-purpose sands. Molds are classified as green-sand, dry-sand, skin-dried, and chemically hardened molds; those in the last category may be hardened by carbon dioxide, or they may be self-hardening. The properties of a molding sand—formability, strength, gas permeability, refractoriness, and collapsibility—depend on the combination of materials used and the way in which the materials are mixed. Recycled sands may also be used as molding sand. Special production equipment is used in the manufacture of molding sands.