The Challenges of Stone Veneer

Stone siding might be the most problematic siding that my company comes across as home inspectors. This material is failing left and right all over the country, and most of the time the homeowner has no idea when their wall is a rotted mess behind the siding.

I’m calling it stone siding because that’s what everyone knows it as, but what I’m really referring to is a product called Adhered Masonry Stone Veneer, or AMSV. This is a man-made product that looks like stone siding but performs like stucco. Well, lumpy stucco, to be more specific.

We Find Problems

While masonry veneer looks great, it’s susceptible to the same moisture problems as stucco. We’ve tested dozens, possibly even hundreds, of homes throughout the Twin Cities (Minneapolis and St. Paul) that have stone veneer siding, and we’ve found that these homes experience the exact same type of moisture intrusion problems as newer stucco but worse.

How to Do It Right

While the newest stucco installations are done quite well, the folks installing stone veneer almost never get it right. When we inspect stone veneer, we use the National Concrete Masonry Association’s installation guide. To understand how important this guide is, here’s some background, directly from one of their engineers:

When masonry stone veneer (MSV) was first introduced into the market, manufacturer recommendations were the only available guidelines to install the product as there were no industry-wide practices or standards.
In 2009, The Masonry Veneer Manufacturers Association (MVMA) created the industry-wide installation recommendations. In 2012, MVMA became part of the National Concrete Masonry Association and we pursued a product and an installation standard through ASTM. That is how ASTM developed the ASTM C1670/C1670M—Standard Specification for Adhered Manufactured Stone Masonry Veneer Units, and ASTM C1780—Standard Practice for Installation Methods for Adhered Manufactured Stone Masonry Veneer. Both are now widely used and are referenced in the TMS 402/602-16 Building Code Requirements and Specification for Masonry Structures that in turn is referenced by the IBC code.

In short, the installation guide referenced on the previous page is the standard that should be followed everywhere. This is the way to do it right. Whether that standard is adopted will vary throughout the country. And even when it’s adopted, enforcement of that standard varies wildly.

Installation Guide

The Installation Guide for AMSV is packed with diagrams showing how to install the material and forms the basis of ASTM C1780. It’s extremely helpful. Every home inspector ought to have a copy of this guide and be familiar with the installation requirements.

As I mentioned, we find the same installation shortcomings over and over again. To help you understand how widespread these issues are, I’ve taken several installation diagrams from the AMSV guide and edited them down to more clearly illustrate where the installations went wrong.

As a home inspector, I don’t get to see all of the different layers of materials that get installed behind the stone veneer; my inspection is limited to what I can see on the surface, and that’s what I report on. To make the installation diagrams easier to understand, I’ve removed the labels of all the components that aren’t visible during the course of a home inspection.

Missing Bedding Seal at Flashing

This is never done right. Never. We verify this by slipping a putty knife underneath the flashing (A). When it’s not done right, wind-driven water will leak behind the siding at this location.

We shouldn’t be able to put our putty knife underneath the flashing like this (B). This means it wasn’t installed properly, and this is all we ever find.

Too Close to Grade or Hard Surfaces

Masonry veneer should be kept at least 2 inches above hard surfaces, such as concrete, and 4 inches above the soil (C).

When the material is buried in dirt, water can wick up into the material and cause rotting at the wall (D).

There should also be a 2-inch gap to paving, but this is often not done. How is water supposed to get out at the bottom? (E)

Of course, leaving a 4-inch gap at the ground isn’t the prettiest looking thing in the world, but there is a solution; simply have the weep screed terminated at least 4 inches above the ground, and have another layer of masonry veneer installed as shown (F).

(G) shows this detail done properly.

Here’s a close-up (H); note the weep screed.

Improper Vertical Transitions

When masonry veneer has a vertical transition to something like wood trim, windows, or other siding materials, it should have a ⅜-inch gap left between the two materials. This gap needs to have a foam backer rod pushed behind it and then filled with sealant to help prevent water intrusion. This is rarely done (I).

Here’s the detail for windows (J).

This is what it looks like when it’s wrong at a vertical transition (K).

And here’s another improper installation, with the mortar tight to the window (L).

Clearance to Roof Coverings

Masonry veneer needs to be kept 2 inches above roof surfaces to help prevent water from wicking up into the wall (M). Here’s a common deviation, where the masonry veneer actually touches the shingles (N). This is just asking for trouble.

Improper Vent Penetrations

Dryer vents, kitchen exhaust vents, bath fan vents, and other similar vent terminals should be pushed against a bed of sealant (O), but they’re often buried in masonry. What happens when the vent cover gets broken and needs to be replaced? (P)

Improper Faucet Installations

Just like dryer vents, exterior faucets need to be embedded in sealant on the surface of the masonry veneer (Q), not buried behind the veneer (R). What happens when the faucet needs to be replaced?

How many bloody knuckles will this installation cause?

The nice thing about the installation is that they got the vertical transition correct; check out that thick bead of caulk.

Of course, this is only a partial list of the things that can go wrong on a stone veneer installation. When you inspect a home with AMSV, be sure to compare what you’re looking at to the manufacturer’s installation instructions and document any installation errors. But it’s also important to help your clients understand the gravity of your findings. Not all of these issues need to be addressed, but they will all increase the likelihood of water problems.

If there’s a small feature of AMSV on the front of the house and it’s well protected from water with large roof overhangs, it’ll probably function fine even when installed improperly. On the other hand, AMSV that’s improperly installed on a gable wall is far more concerning because of the amount of water that will hit the wall. In those cases, I frequently recommend intrusive moisture testing.

To find someone in your area who is qualified to perform intrusive testing, I recommend using the “Find a Professional” link on the Exterior Design Institute website at exteriordesigninstitute.org.

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