Cast stone and concrete has been used in architecture and sculpture for hundreds of years as a means to mimic or replace more costly natural stone. It is a unique medium typically consisting of cement and selected crushed stone, such as limestone, sandstone, marble, and granite. The mixture is usually cast, ideal for the replication of architectural units and garden sculpture, but can also be sculpted after initial set has begun and carved after full curing. Once completed, the finished surfaces are washed or polished to expose the desired aggregates.
Many objects have interior iron armatures for added strength, particularly for extended forms and figurative appendages. Cast stone is susceptible to surface cracks from shrinkage, thermal expansion, particularly differential expansion from armatures, aggregate expansion from alkali-silica reactions, and freeze-thaw cracking. Once points of water ingress are formed from open cracks, armatures are in threat of corrosion expansion and staining, and interior cements in threat of leaching carbonates. Treatments require adequate material analysis and appropriate treatment materials and procedures compatible with the historic original. Attention to identification of the historic aggregate and new aggregate selection is of particular importance.