Improper Stone Veneer Installation Practices

In this very common example shown to the left, 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.

C1780 Figure 8b 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.

C1780 Figure 5b 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 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.

780 Figure 17a

In cases where there is veneer on a sidewall above a roof, a gap of, at least, 2” should exist above the roof. 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

This detail covers where AMSV terminates at things like doors, windows, or other vertical joints like 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.

(photo 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.