What is Manufactured Stone Veneer?
Manufactured stone exterior cladding system has been around since 1962, the 1920’s, or the 12th Century depending on the criteria used to establish its historical beginning. However, the use of manufactured stone cladding, especially over common wood framing, became much more popular over the past few decades. The increase in its use, and thus, its being tested in real weather exposures has brought to light deficiencies with the various installation practices and methods. Learning from past failures the adhered manufactured stone veneer industry has been slowly developing installation methods that reduce the risk of the various modes of the observed failures. Most changes in the installation methods have dealt with addressing issues with the unwanted infiltration of rain water and movement cracking. The most recent standard is Installation Guide and Detailing Options for Compliance with ASTM C1780, 4th Edition, 2014.
Prior to the development of the first consensus standard in 2013, installation methods were generally determined and provided through recommendations by the stone manufacturer. This practice resulted in various installation practices and methods. Some of these practices were not as good as others.
During our evaluation of failed manufactured stone veneer we have noticed the following:
- A thicker mortar bed, approximately one inch thick, provides a stiffer cladding, a more water resistant cladding, and better protection of the metal lath and fasteners from corrosion.
- Narrower mortar joints between the stone units provides better resistance to rain water infiltration, and thus, reduces the risk of corrosion of the metal lath and fasteners.
- Proper flashing at the interfaces with windows, doors, roofs, etc. reduces the infiltration of rain water into the wall and reduces the risk of the corrosion of the metal lath and fasteners, decay or corrosion of the components in the wood frame back-up, and leakage into the interior.
- Installation of expansion joints that divide large surfaces areas of stone in smaller section to allow expansion. Expansion joints reduce the risk of cracking which allows the infiltration of rain water and reduces the risk of the stone bulging out away from the wall from buckling.
- A double layer of roofing paper or a rubberized water proof membrane reduces the risk of water infiltration into the structural back-up for the cladding. See Figure MS-1.