There is often confusion in both terminology and physical properties on many construction documents when a material is called out as “cast stone” or “adhered stone veneer.” This article clarifies the differences in the two products.
There are substantial differences between the physical properties of cast stone and adhered veneer that should be considered when specifying.
Adhered veneer is a lightweight product that is applied to a structural wall with an adhesive. Therefore, it cannot be used to add to the load-bearing capacity of the wall. Cast stone, however, adds to the load-bearing capacity of a masonry wall and is usually integrated into the brickwork, becoming part of a composite wall system rather than being adhered to it.
Cast stone provides additional strength because it is anchored within the masonry structure and stands the test of time. While adhered stone products are made light in weight so they will work easily on the exterior of other wall materials, cast stone weighs approximately the same as natural cut limestone.
Test methods dictate how the materials are evaluated, while the specification stipulates what the requirements of the test results must be, as well as the ingredients each product must contain.
For example, cast stone is required to have a minimum compressive strength of 6500 psi, maximum moisture absorption of 6%, and a unit density of approximately 135 pcf. The minimum compressive strength of adhered veneer is approximately 1800 psi to 2000 psi, absorption may reach 22% (UBC Standard 15-5), unit density is approximately 75 pcf, and much emphasis is put onto a shear bond test which is presently under development.
Each product must pass a rigorous freeze-thaw test. Because adhered manufactured stone masonry veneer (AMSMV) is an adhered unit, most building codes such as UBC/IBC, require the maximum density to be 15 lbs/sq ft, and allow the minimum thickness to be approximately ¼ in. Cast stone, when used in a conventional 3 5/8 -in. thickness, weighs about 40 psf.
In cast stone, a high percentage of durable fine aggregate in any man-made stone creates a very smooth, consistent texture for the building elements being cast, resembling natural limestone, brownstone, sandstone, marble, or granite. Applications that use cast stone range from the simplest window sill to the most complicated classical architecture. Therefore, the number of profiles and sizes required for any given project can vary from a single shape shown on a sketch to hundreds or more, perhaps not so clearly indicated in a set of architectural contract documents.
AMSMV usually has a natural quarried stone appearance and can be used for many of the same applications, although it is primarily considered an adhered veneer.
Both products have many of the same properties inherent in a material which is primarily intended to simulate natural building stone, although cast stone is typically custom made to approved shop drawings and AMSMV is most often laid out and cut to suit field conditions.