An Education in Architectural Cast Stone
Architectural cast stone is a quality masonry product simulating natural stone.
By Jan Boyer
If it looks like stone and is a manufactured concrete product, then it must be cast stone, right? No, not true. The product could be cast stone or one of a number of other products, including adhered manufactured stone masonry veneer (AMSMV), architectural precast, calcium silicate, natural stone or even new lightweight products made with only an outer coating of concrete. Each product has its appropriate applications, dependent upon the project. Here is all what you need to know about architectural cast stone
What is cast stone?
Architectural cast stone is a refined architectural concrete building unit manufactured to simulate natural cut stone and used in unit masonry applications. In other words, it is a unit that is installed by a mason.
Used as an architectural feature, trim, ornament or veneer for buildings or other structures, it is created with a fine grain texture to simulate all types of natural cut stone, including – but not limited to – limestone, granite, slate, travertine or marble. Cast stone can be made from white and/or grey cements, manufactured or natural sands, carefully selected crushed stone or well-graded natural gravels, mineral coloring pigments and admixtures to achieve the desired color and appearance, while maintaining durable physical properties that exceed most natural cut building stones.
Architectural cast stone is generally non-structural and anchored to load-bearing masonry wall systems in traditional commercial and residential buildings, and other structures. It is also used in numerous hardscape applications and is often the material of choice for restoration projects, where it can easily replicate intricate natural stone original pieces.
Proper specification of cast stone
Architectural cast stone is specified to be manufactured to meet or exceed standards as per the current version of the ASTM Standard Specification for architectural cast stone, which originated in 1997. In this document, there are specific requirements for the physical properties, testing, appearance and tolerances for cast stone. These requirements are applicable, whether the product is manufactured by dry tamp, wet cast or machine made methods.
ASTM C-1364 is referenced beginning with the 2012 International Building Code as the definition for Cast stone and is, therefore, legally binding in jurisdictions that have adopted the building codes. Cast stone requirements address compressive strength, absorption, freeze-thaw issues. Visit CastStone.org/specifications.htm for more detailed information. You may also reference the Cast Stone Institute Technical Bulletin #54 at CastStone.org/bulletins/54.html.
Cast Stone Institute plant certification
Recognizing the importance of quality cast stone production to the viability and longevity of a structural or landscape project, the Cast Stone Institute developed a plant certification program 15 years ago. Over the years, this certification program has been enhanced to make it one of the most rigorous certification programs in the construction industries. The CSI Certified Producers take great pride in the production of exceptional cast stone for each project for which they supply material.
In order for a non-certified producer plant to be considered equal to a CSI Certified Plant, there are specific and important criteria that a specifier should require as documentation. Simply stating that a plant complies with CSI Certification Guidelines is not enough. Prior to admission, each potential Producer Member must submit to a rigorous examination of product quality, safety, testing (including freeze-thaw), meticulous record keeping and financial viability of the company.
Once certified, they undergo the recertification process every other year with unannounced inspections and test data reporting every six months, in addition to numerous other requirements.
The following two tests must be performed for every 500 cubic feet of Cast Stone produced and passing reports available for review for at least the most recent six months. These tests can be performed in house or by independent testing laboratory. Each test must also be performed at least every six months by a qualified independent testing laboratory that has successfully passed the CSI Testing Technician Training Course. Note that this required testing is completed on 2-inch cube samples and not by cylinders as per ASTM requirements.
- Compressive strength must be at least 6,500 psi at 28 days (ASTM C1194).
- Absorption must be less than 6 percent with a cold water test at 28 days (ASTM C1195).
A passing freeze-thaw test, ASTM C666, by a qualified independent testing laboratory should be available for each mix design. This test measures product weight loss after 300 cycles of rapid freezing and thawing in a wet environment with cumulative percentage mass loss less than 5 percent required for passing. Freeze-thaw testing shows durability of the cast stone over time, and it is a good indicator of quality cast stone production.
10 Year Product Warranty
Continuing to lead the industry, the Cast Stone Institute Producer Members adopted language for a 10 Year Limited Product Warranty in 2011. CSI Producer Members are aware of the evolving environment for products in the marketplace that demand sustainability, durability and useable service life. This warranty demonstrates that CSI Producer Members embrace these principles and produce product that will stand the test of time. Cast Stone Institute Technical Information, Details, Or Equal and Warranty documents are available at CastStone.org.
Jan Boyer has been the Executive Director of the Cast Stone Institute since 2006. She can be reached at email@example.com. To see photos of the many uses of cast stone, visit CastStone.org/photographs.htm. The Masonry Society offers Standards for Architectural Cast Stone, https://MasonrySociety.org/product/tms-0404-16.