Adhered Manufactured Concrete Stone Veneer (Part 4)

JNX-clusives

Chips Off the Old Block

and other ruminations about masonry 

by

Larry D. Jenks

 

Adhered Manufactured Concrete Stone Veneer

 Since my last installment, I have exchanged some thoughts with my friends Diane Travis, Technical Director at the Rocky Mountain Masonry Institute, and Mike Schuller of Atkinson-Noland + Associates. I will try to provide a synopsis of those discussions for you to ponder.

The main thing that makes an Adhered Manufactured Concrete Stone Veneer (AMCSV) different than EIFS from a moisture intrusion perspective is that the AMCSV system will  absorb water that comes in contact with it, and keep it from penetrating unbridled to the Water Resistive Barrier (WRB). That gives it time to evaporate. The EIFS systems, including the drainage systems I discussed briefly earlier, don't have water-absorbing materials, and water continues to migrate through the finish materials to the WRB. If a drainage system is not provided, the water stays held against the WRB, and eventually causes it to fail.

Here's what the IBC says about all of this...

According to the International Building Code (paragraph 1403.2 Weather Protection):

“The exterior wall envelope shall be designed and constructed in such a manner as to prevent the accumulation of water within the wall assembly by providing a water-resistive barrier behind the exterior veneer, as described in Section 1404.2 and a means for draining water that enters the assembly to the exterior of the veneer…”

The Commentary to the Code explains further:

“The method to provide the means of drainage is a performance criterion and must be evaluated based upon the ability to allow moisture that may penetrate behind the exterior wall covering to drain back to the exterior.  This may be as complicated as a rain-screen pressure-equalized type of exterior assembly or as simple as providing discontinuities or gaps between the surface of the substrate and the back side of the finish, such as through the use of non-corrodible furring.”

This says, to me, that a provision must be made to allow water to drain back out of the system. The code doesn't say anything about the ability of the system to achieve evaporation. But also keep in mind that in many parts of Colorado and the southwest, moisture events can be few and far between. In these cases, there is likely to be ample opportunity for adequate evaporation to occur. That said, rain screens or drainage mats add time and costs to projects, and their use should be weighed carefully. But clearly, the drainage mechanism can be a simple one, such as a dimpled mat. This strikes me as something you would want to discuss with your local Authority Having Jurisdiction (AHJ) before making your final decision. So please let me know if you find an AHJ that does not require some kind of drainage mechanism. The status of this system seems to be in flux, and we all need to monitor its evolution. While this plays out, my recommendation would be to play it safe. It may be short-sighted to opt for the pretty, the fast, and the cheap. You can quote me on that (but Diane said it first).