While cast stone has been a popular building material since the 1920s, it's hard to pin down an exact definition for this versatile product class. The American Concrete Institute defines cast stone as “concrete or mortar cast into blocks or small special molds so as to resemble natural building stone.”
In ASTM C 1364, the Standard Specification for Architectural Cast Stone, the committee defines cast stone as “an architectural precast building unit intended to simulate natural cut stone.”
The Cast Stone Institute best defines its members' product as “a refined architectural concrete building unit manufactured to simulate natural cut stone used in unit masonry applications.”
In practice, cast stone is a masonry product, used as an architectural feature, trim, ornament, or facing for buildings or other structures. As such, its placement is governed by masonry specifications, often within the jurisdiction of the Masonry Standards Joint Committee and other masonry associations.
Unlike veneer stone, cast stone conforming to the ASTM C 1364 standard requires substantially different physical requirements than cultured or simulated stone products. Since cast stone is often used as a structural member, it must have a minimum compressive strength of 6500 psi, a maximum absorption of 6%, and pass a rigorous freeze-thaw test.
In simplest terms, cast stone differs from architectural precast in two ways. First, the cast stone elements are normally smaller and designed to be included in a masonry assemblage. Second, a mason usually installs cast stone.