Masonry Magazine December 2005 Page. 25
There are substantial differences between cast stone and simulated stone. Simulated stone is a lightweight product that is adhered to a structural wall. Therefore, simulated stone cannot be used to add to the load-bearing capacity of a masonry wall. In addition, while simulated stone products are made light in weight so they will work easily on the exterior of other wall material, cast stone weighs approximately the same as natural cut limestone.
Cast stone has an ASTM standard specification, C 1364, which has substantially different physical requirements than cultured or simulated stone products, which usually reference ASTM test methods. Test methods simply dictate how materials are tested, while the standard specification stipulates what the test results must be, as well as the ingredients the product must contain. For example, cast stone is required to have a minimum compressive strength of 6,500 psi and maximum absorption of 6%. It must have a fine-grained texture similar to natural stone and pass a rigorous freeze-thaw test. The dimensions of each unit may not deviate by more than 1/8-inch from approved dimensions, and it is reinforced with billet steel reinforcing bars, unless otherwise specified, according to ASTM C 1364 - Standard Specification for Architectural Cast Stone.
Design Considerations
SHRINKAGE AND VOLUME changes are top design considerations for masonry wall assemblies, and the concerns for cast stone can be divided into two categories: shrinkage and cracking of cast stone veneer assemblies, and shrinkage and cracking of individual cast stone elements.
The first category applies to cast stone used as a veneer or in combination with concrete masonry veneers. In this case, the recommendations from the National Concrete Masonry Association (NCMA) seem appropriate. NCMA recommends that control joints be placed at a maximum spacing of 25 feet and that the aspect ratio of the wall is such that the length of the wall is no more than 1-1/2 times the height of the wall. Thus for an eight-foot high wall, vertical control joints should be spaced at 12 feet. These recommendations from NCMA also take into account reversible thermal and moisture movements and are based on extensive research and field experience.
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December 2005
Masonry 23
The Voice of the Mason Contractor