Stucco, exterior insulation finish systems (EIFS), brick veneer, manufactured stone veneer, and cheap thin stone or faux stone siding often get bad reputations when it comes to installation defects in masonry construction because of improper moisture management. But even the best natural stone veneer, whether full or thin stone, is doomed to fail from water damage if moisture stays trapped in the wall. That’s why our staff of experts at Buechel Stone spent some time with Tyler LeClear Vachta, Marketing & Education Manager with Masonry Technology Inc., to learn more about how to prevent moisture problems with full and thin stone wall systems. He was so well-spoken on the topic that we requested his permission to pass along his expertise using his exact presentation, so that’s what we’re doing here. Watch his narrated video (embedded below) or scroll down this blog post to absorb the information at your own pace.

This Press & Blog post looks at how to prevent moisture problems in full and thin stone veneer masonry construction. Flashings, building paper, and house wrap probably come to mind, and these are important components. But even with those materials, we’ve seen an increasing trend of failures. While EIFS and stucco get a bad reputation, stucco and thin stone face the exact same issues, and now with exterior rigid insulation behind stone we are re-creating the EIFS scenarios that led to trouble in the 90’s.

The photos above illustrate just some of the examples of failures in relatively new buildings, some of them less than a year old. We see house wrap and building paper. While sometimes there are obvious flaws in the detailing, there are cases where the assembly experienced normal wetting but just couldn’t dry. Over the years, we’ve seen many instances where an extra layer of building paper was added in an attempt to protect the wall. But a ‘belt and suspenders’ approach of adding another barrier doesn’t do very much.

The above image shows some of the EMC components. At the far right, we see the EMC-3639 drainage mat, with vertical channels and mortar-blocking fabric. (There are two sizes on the Buechel website, linked here: EMC-3639 and EMC-3639XL.) The vertical channels allow moisture to drain to the bottom of the wall and exit. And the mortar-blocking fabric protects those channels so that the mortar doesn’t clog them. The fabric is also wrapped around the back so that we have an insect guard at terminations.

At the bottom, you can see a LR-3639 WEEP screed, made of galvanized steel. This WEEP screed is a little different. There’s large slots to drain liquid water and allow air flow to ventilate the rain screen air gap. An air gap is allowed by code to replace the outer layer of building paper or house wrap. (Please verify with local codes.)

Testing shows that rain screen systems perform significantly better than code-minimum systems. The above lab test compared a code-minimum wall with two layers of paper, lathe, and scratch coat to a system with the building paper, rain screen drainage mat, lathe, and scratch coat. Moisture sensors were embedded on the face of the sheathing and each layer of paper to measure moisture over time.

So let’s look at the components a little closer, and then we’ll get to detailing in just a minute. The full wall air gap over the building paper or house wrap, is maintained by the EMC-3639 which is vapor-open to allow the system to dry to the exterior.

At the base of the wall, we need to let liquid water exit. With full width stone veneer, we can use the SCW-3639 or WOW-3639. They both create tunnels for drainage on the flashing. They work better than rope WEEPs, which don’t wick very well, or tube and vents that end up above the bed joint mortar.

With adhered stone we can use the WOW-3639 or the LR-3639 WEEP screed, which has large slots for drainage and ventilation.

Any time that we have an interruption in the drainage plane, such as at a window or door, we need to let the water escape or divert it. The WOW-3639 WEEP is used on window drip cap flashings to let the water exit the wall in full or thin stone veneer. The MD-3639, or moisture diverter, can be used to divert moisture from the drainage plane away from the rough opening in inset applications, or as a ‘belt and suspenders’ approach with the WEEPs.

Another common detail is a stone siding transition. The EMC-3639 can also be used behind siding. At transitions such as a stone wainscoting, flash the upper detail at the cap stone.

On the right (above) we have a window detail. At windows, install the WOW-3639 WEEP above the drip plate with the EMC-3639 fabric lapping over the WEEPs. This prevents the mortar from clogging the WEEPs. On inset windows where WEEPs are not practical, use the MD-3639 moisture diverter to divert moisture away from the opening. Install the MD-3639 at a quarter inch per foot slope to drain immediately above the opening. Extend it four inches beyond the opening on both sides. Terminate the EMC-3639 in the moisture diverter.

Two other important details include the soffit (pictured below). For maximum drying, we want to vent the EMC-3639 below the soffit. Leave a small gap for ventilation between the termination and the soffit board. Use a soffit trim board to protect against wind-driven rain.

On the right (above) we have a wall-to-roof intersection with a very important masonry installation detail. The kick-out flashing used in this detail is a fifteen-dollar piece of metal or plastic that can prevent $30,000 dollars in repairs.