Improper Stone Veneer Installation Practices

Adhered Masonry Stone Veneer (also known as AMSV) is a product used on many newer (say, the past 30 years or so) homes in our area, although it is rarely properly installed based upon my experience. I’ve inspected lots of newly constructed homes for buyers just in the past 5 years and have not seen a proper AMSV installation yet.

In 2009, guidelines from the Masonry Veneer Manufacturers Association (MVMA) were introduced. Prior to that, only manufacturer installation guidelines really existed and those were often confusing to some installers, builders, home inspectors, and code officials. These guidelines were used to create a document considered the standard for AMSV installation, called ASTM C1780: Standard Practice for Installation Methods for Adhered Manufactured Stone Masonry Veneer. Homes with stone veneer installed that were built prior to this time frame will generally only have the items shown below if they were repaired or otherwise modified later on after installation.

This ASTM document outlines how this product should be installed and includes many (48, to be exact) helpful diagrams to use as reference to show many different situations and locations on a home’s exterior where this product is to be installed.

Adhered Masonry Stone Veneer is often installed along the lower portion of a home’s front exterior (such as below another type of siding) or sometimes is installed to cover the entire front (or more) of a home. Sometimes the product is only installed over the exposed foundation and another siding product serves as the home’s exterior cladding from the sill plate upwards.

I’ve inspected nearly 80 homes in a new development in the area and repeatedly call out the same flaws for each home. In this case, it commonly relates to the lack of sealant below a piece of metal flashing that is installed where vinyl siding terminates on top of a stone ledge. The stone ledge serves as the top of the stone veneer (a transition, if you will) installed below it.

In this very common example shown to the right, the red arrow is pointing to the underside of a piece of metal flashing that runs upwards a short distance (out of view) behind the vinyl siding and then is bent outwards to extend out laterally across the top of the stone ledge. The flashing is meant to help catch any water than may get behind the lower end of the siding and area around the stone ledge. Figures 3, 8a, and 8b of ASTM C1780 each show a bead of sealant to be installed along the underside of this flashing, yet it is almost never done. I’ve included figure 8b of C1780 below to illustrate how this detail is supposed to be done. Notice the items in red.

These proper flashing and sealant details are important in order to help prevent water entry into an exterior wall where hidden rot and mold (and/or insect infestation) can then occur unbeknownst to the homeowner for a period of time.

C1780 Figure 8b below illustrates the need to apply the “bedding sealant under flashing”. It means, properly caulk the underside of this flashing which sits on top of the ledge.

This sealant is supposed to be installed to help prevent wind-driven rain from entering behind the stone veneer at this location. I either use a screw driver or my finger to check this area. For whatever reason, most builders do not perform this detail as required.

I’ve actually asked a few builders about this in the past. Each time, the reply was along the lines of ‘we’re hoping that the house wrap behind the veneer will catch and shed the water’.

I’ve also asked a code official who was doing a final inspection on a brand new home as I was performing the buyer’s home inspection. His reply was that he was ‘not too familiar with the requirements’ and that ‘it’s up to the product manufacturer to tell the builder how to install the product’. The lack of following proper guidelines and the lack of knowledge of the installers and code officials is a good re-enforcement of why buyers of even brand new homes should always get their new home inspection performed.

Another related issue that I run across pertaining to AMSV deals with how these products are terminated along grade, roofs, windows/doors, and flat hard surfaces. Improper installation at these areas can prevent proper drainage from the AMSV and can allow for the absorption of water into the exterior wall structure.

C1780 Figure 5b above shows that stone veneer should terminate, at least, 2” above hard flat surfaces (ie, driveways, steps, or patios) and, at least, 4” above grade. There is a weep screed (normally a plastic piece with small holes in it) shown in the red circle installed which hangs down below the veneer to allow water to drain out that may have penetrated behind the veneer. The weep screed’s openings need to be fully open to atmosphere and should not be buried in soil or mulch or caulked.

Figure 7 of C1780 to the right shows an example of where the veneer is extended down onto the foundation. The weep screed would still be installed above grade (see its location in the red circle) and the veneer continues below the weep screed.

The veneer below the screed is not installed against wood structure but only against the foundation wall.

C1780 Figure 17 above shows a, minimal, 2″ gap between where sidewall veneer and a roof below it meet. This gap helps allow water to drain out of the screed and also makes future roof replacement easier. A weep screed can be seen hanging down below the veneer for drainage.

Note – Manufacturers of composite siding and stucco products also call for, at least, a 2” gap in this location. At homes with wood siding, I often find the siding installed directly against roof shingles and the lower edge of the siding often has chipping paint and/or rot due to the installation method.

C1780 Figure 22 to the right shows the details needed at joints where AMSV terminates at doors, windows, and other vertical joints such as another wall.

This diagram looks rather cluttered due to all of the components and details needed. This view is looking downwards into the exterior wall (home’s interior is at the top and exterior is at the bottom). A 3/8” perimeter gap is supposed to exist at these junctions where backer rod is installed (see red circle) and then the opening is properly sealed with an elastomeric sealant. These gaps with backer rod installed give room for expansion/contraction of the materials (the masonry and the door or window) and the sealant is meant to prevent water entry yet remain flexible. For doors and windows, the gap should exist around the entire perimeter where the AMSV contacts the window or door. Mortar should not be installed tightly right against a door or window. The photo below shows an example of a properly sealed joint where stucco joins a window; the detail is the same for stucco, brick, or stone. The sealant used is semi-flexible and does not harden like regular caulking.

The photo above shows an example of a properly sealed joint where stucco joins a window; the detail is the same for stucco, stone, or brick. The sealant used is semi-flexible and does not harden like regular caulking. (Photo is courtesy of AK Windows).

Another concern is where things penetrate through the AMSV such as receptacle boxes, faucets (aka hose bibs or hydrants), clothes dryer vents, etc. These items should be pushed into a bead of flexible sealant (elastomeric) instead of being cemented into place within the veneer. Doing so helps prevent water entry into (and possible rotting of) the adjacent wall as well as easy repair if any of these items need to be replaced in the future.

Kickout flashing, such as where gutters terminate against a sidewall, is also still, of course, needed to help prevent water damage at exterior walls covered in stone, brick, stucco, cement fiberboard, etc. Learn more by reading my Kicking Flashing article.

Learn more about the installation of AMSV from the National Concrete Masonry Association. This is an excellent article!

Also, here is a Mason Contractor’s newsletter article on the topic.

Matthew Steger is a Certified Level 1 Infrared Thermographer, an ASHI Certified Inspector (ACI), and an electrical engineer. He can be reached at: matthew@thehomeinspectorsnotebook.com

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