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Green Basics

Stone and Synthetic Stone

A Traditional Look That Requires a Drainage Mat and Vapor-Impermeable Sheathing

Stone veneer that is 8 inches thick weighs 6 tons or more per 100 square feet. Stone veneers must be set on a solid masonry ledge built into the concrete footing, which means more concrete than for an unveneered foundation. Setting stone is labor-intensive, and skilled masons may not be as easy to find as carpenters who can install other types of siding.

Manufactured stone is lightweight concrete that has been molded and colored to look like building stone. It costs one-third to one-half as much as real stone veneer, and it’s light enough to adhere to a wall without any special footing for support.

Manufactured stone is made in a variety of colors and patterns but, unlike natural stone, the coloration is only on the surface, so cut edges must be concealed in the mortar joint.

Installation pitfalls

Many unwary builders have been plagued by callbacks after installing natural or manufactured stone veneer over OSB sheathing. Installers typically apply wire lath over two layers of #30 felt and adhere the natural or manufactured stone to the wall with mortar. This installation method, however, has been associated with a rash of catastrophic failures, especially on walls with OSB sheathing. Unless a three-dimensional drainage mat or dimple mat is included between the two layers, little drainage may result.

Stone veneer and manufactured stone are reservoir claddings, meaning that they absorb and hold water after a rainstorm. Once the sun comes out, the wet cladding tries to dry in both directions, which can push moisture into the building, a process called inward solar vapor drive.

A well-detailed stone veneer installation requires vapor-impermeable sheathing to slow inward solar vapor drive. In most cases, extruded polystyrene or polyisocyanurate foam are the best sheathings to use under stone veneer. Vapor-permeable sheathings like Celotex should never be used…

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2 Comments

  1. Beyhan Trock | | #1

    Stone Walls
    What can you tell me about how to penetrate XPS with ties attached to studs to support true 4-6" stone on the exterior walls?

  2. User avater GBA Editor
    Martin Holladay | | #2

    Beyhan Trock
    Beyhan,
    GBA has many details for stone veneer; if you become a GBA subscriber, you'll have access to all of these details in our detail library. Here is a link to an example:

    https://www.greenbuildingadvisor.com/cad/detail/flanged-window-sill-exterior-foam-sheathing-stone-veneer-siding

    Many manufacturers sell brick ties or stone veneer ties designed for walls sheathed with rigid foam. Google "brick ties for rigid foam" and you'll discover these manufacturers. Here are some links:

    http://www.ctpanchors.com/ctp-16.aspx

    http://rodenhouse-inc.com/products/pos-tie-veneer-anchoring-system/

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