FAQ's

Do you need a Drainage Layer behind the Adhered Stone Veneer?

While installing a dedicated sheet of drainage material provides a sure and quick way to wick water out of the wall before it penetrates the sheathing, a commercial drainage fabric is not required by Code.

Paragraph 1403.2 of the IBC calls for A water-resistive barrier behind the exterior veneer and a means for draining water that enters the assembly to the exterior of the venee”. According to the Commentary to the Code, this assembly has three parts: A water-resistive barrier installed over the substrate; flashings at penetrations and terminations of the exterior wall finish and a means of draining moisture that may penetrate the finish back to the exterior. The Commentary states that this drainage plane 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.

Moisture running through a commercial drainage products typically moves much more quickly than water seeping down the thin gaps between the expanded metal lath and the moisture barrier. Drainage sheets help the whole wall dry out more quickly. This is important because saturated masonry is prone to mold and mildew in hot climates. It is susceptible to fracture in cold climates with serious freeze thaw cycling issues. Using a drainage plane will significantly lower your risk of damage from moisture penetration.

My window sill stones are 2″ x 24″ x 4″.  When they are installed, the 4″ dimension is nearly horizontal. Can it still be installed as an adhered veneer?

No. The Code limits the depth of adhered veneer to 2-5/8″ or less. This dimension is to be measured horizontally as installed. The piece of stone that you are using as a sill projects 4″ from the sheathing of the wall. This exceeds the size allowed for adhered veneer installation.

You have two options: You can either use a metal sill or you can install a steel angle under the stone sill and treat that stone as a piece of Anchored Stone Veneer. The steel angle under the sill does not need to be continuous or particularly hefty. It is not supporting much weight. It does, however, need to support 2/3 of the horizontal projection of the stone. See Detail xx for more information.

Can you bury the base of an Adhered Stone Veneer below grade?

The base of the wall is susceptible to premature failure because of the moisture in the soil. We understand that the architect wants the building to look like it is built with massive pieces of stone. This illusion of load-bearing masonry is shattered if the stone veneer is held several inches above grade. Unfortunately, the Code does not allow you to let many materials touch the ground. Stucco, wood siding, most sheathing materials, wood studs and steel studs must all be held above the ground. Masonry materials (concrete, concrete block, brick and stone) are robust enough to touch the grade.

While we never recommend burying a thin piece of Adhered Veneer Stone in the ground, you can bury natural stone veneer in the ground if you install it over concrete block or poured-in-place concrete without a layer of rigid insulation or metal lath behind it. If you choose to take this path, please use natural stone that has low absorption. Contact the stone supplier to see if your thin stone veneer would survive being buried in the soil.

Is there a test that will predict the durability of a specific type of stone?

Although the C-18 Committee of ASTM has been working on developing an accelerated weathering test to predict the durability of stone, they have not yet agreed on appropriate test methods. At present there is no test for stone durability. It is not appropriate to use ASTM C-666 on stone. C-666 is a test for durability of concrete. Until ASTM publishes their new standard, our best advice is to use a type of stone that has performed successfully on other buildings in your area.

When in doubt, be conservative. Thick pieces of stone usually fare better than thinner stones do. In climates with a lot of freeze/thaw cycling, stones with a low absorption coefficient typically last longer than porous stones do.

How stiff does the substrate behind the Adhered Stone Veneer need to be?

Both wood studs and steel studs are quite flexible. They bend a bit in response to applied loads. This can cause cracks in the inflexible stone veneer. These cracks usually show up at the middle of the wall, the point of maximum bending. These cracks can let water into the wall which may lead to premature failure.

For years the Brick Industry Association has recommended that the studs behind an anchored brick veneer be designed to limit bending to L/720. Since the L factor in this formula is expressed in inches, the L factor for a 10′ tall wall would be 120″. The allowable deflection for this wall would be 120/720 or 0.167″ (slightly less than 3/16″).

Since Adhered Stone Veneer is thinner than anchored brick veneer and because it is glued to the substrate, we feel that we need a slightly stiffer structural system behind our veneer to minimize the potential for cracking. We recommend an allowable deflection of L/1000 for the stud walls behind Adhered Stone Veneer.

Concrete and CMU walls are naturally rigid and pair well with Adhered Stone Veneer.

Can I install rigid insulation between the Adhered Veneer Stone and the sheathing?

The International Energy Code for Conservation (IECC) calls for a continuous layer of insulation somewhere in the wall assembly. They instituted this requirement to circumvent the thermal bridging factor of the studs which wick away 40% to 60% of the R-value of batt insulation installed between studs. If you want to introduce a layer of continuous rigid insulation in an adhered stone veneer wall, we recommend that you install this insulation on the inside face of the studs, just behind the interior sheathing.

If you insist on installing rigid insulation on the outside face of the studs, you need to realize that the rigid insulation is actually not all that rigid. Point loads from errant baseballs or ladders leaned against the wall can dent the rigid insulation and crack the veneer. To prevent this damage you will need to install a thick layer of cementitious materials over the insulation to provide a stiff, stable substrate upon which to mount the stone veneer. Elsewhere in this Guide we tell you that the cementitious layer behind the stone (scratch coat + mortar bed) should be 3/4″ to 1-1/4″ thick. If you are using rigid insulation behind the stone, we recommend that you aim for the 1-1/4″ thick layer.

Walls with rigid insulation installed under the stone veneer should NOT have the stone veneer touch the ground. While the stone is tough enough to survive this exposure, the rigid insulation, the expanded metal lath and the flashing should not touch the ground or be buried below the sidewalk.

The Code calls for flashing at edges and penetrations in the Adhered Veneer wall. Doesn’t this flashing interfere with the bond between the stone and the wall?

Flashing can indeed cause shear failure in the mortar holding the stone to the back-up wall. This is why you should always install expanded metal mesh on top of the flashing. Fasteners hold the mesh firmly to the substrate behind the flashing and the scratch coat can grip the holes in the metal mesh.

If you are using bitumen ice dam flashing behind the mesh, the bitumen will soften when the sun warms the wall and the tar will self-heal around holes caused by the screws or nails holding the expanded metal mesh in place. If you are using other types of flashing you will need to add a dab of sealant at each nail or screw penetration.

Code says that you do not need a moisture barrier or flashing behind adhered veneer that has been applied directly to concrete or CMU.

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