Think of a stone veneer as stucco with chunks of concrete embedded in it. Those chunks of concrete absorb and hold a lot of water, so you have to have a system that can drain. Otherwise, all that water held in the cladding will eventually find a way inside.

Adhered concrete masonry veneer (ACMV) has been increasing in popularity as a cladding on mid-range and high-end homes for the last decade. According to building consultant, Mark Parlee, a huge number of these homes are now showing signs of water-damage. Parlee believes the problems with ACMV have the potential to dwarf the EIFS failures common in the 1980's and 90's. That's because ACMV is more like stucco with big chunks of concrete in it. Those chunks tend to absorb and hold a lot of water, which will find its way inside if the cladding assembly is not detailed correctly. The primary requirement is to make the assembly drainable, using a well-detailed weather barrier covered by a rainscreen mat.

According to Parlee, most most contractors installing stone veneer treat it as if the stone will shed water instead of absorbing and holding water. ACMV, he argues, is a lot like brick veneer, only we aren't in the habit of installing it with an airspace behind it the way code requires for brick veneer. Look for details on how to create a drainable cladding assembly with ACMV in the upcoming October issue of JLC. Parlee's system builds on the Masonry Veneer Manufacturer's Association Installation Guide [PDF], and relies on a rainscreen  mat, such as one shown in the "Rainscreen Sources" sidebar on this page.