Consultant Talk

Among Buric’s clients, there is constant talk about exterior claddings, especially EIFS and manufactured stone veneer. Problems with EIFS are widely known, and as an alternative, builders have turned to manufactured stone veneer. Robert Klein, Project Consultant, and Bridget Miller, Architectural Designer, both from our Somerville, NJ office, impart some of their knowledge regarding this alternative method of cladding.

As designers and builders have come to understand the inherent problems with EIFS, they have increasingly turned to other materials to provide the aesthetics they previously attained with EIFS. Specifically, manufactured stone veneer, a lightweight, textured and pigmented concrete product resembling stone is being cast as a substitute; however, all is not well with this cladding either.

This veneer system is commonly used in framed construction and normally consists of a metal lath fastened over a weather barrier of tar paper or housewrap installed on the exterior wall sheathing (plywood, oriented strand board (OSB) or fiberglass–faced gypsum).

Stones are then applied by two methods. In a one–step process, stones are “back buttered” with mortar and pressed into a wet base coat of cement plaster previously applied onto the metal lath that anchors the system to the wall. Alternatively, in a two–step process, the base coat is applied to the metal lath and then raked to provide a rough surface for stone–setting on another day that again uses the “back buttered” approach. The installer’s term for either of these applications is “Lick and Stick” stones.

Once the stones are set, the joints are either grouted or not, if the stone were installed by the “drystack” method with minimal joint space. Additional layers of weather barrier may be installed behind the lath as a bond breaker to prevent the base coat from bonding to the original weather barrier. The base coat may bond tightly to the outer housewrap layer rendering little to no air space for water to flow down the weather barrier making the single layer of weather barrier useless as a drainage plane. Sometimes the significant quantity of water entering through the mortar or the stones may deteriorate the outer weather barrier making a second layer advantageous for further weather protection.

In the wake of an ever–increasing tide of construction defect litigation, manufacturers of stone veneer are adding flashing and sealant details to their instructions to counter concerns of water intrusion behind the stone.

What problems have been found with manufactured stone veneer?

The product has been most widely used during the past ten years and Buric is beginning to observe problems associated with the cladding. By nature, all masonry materials are porous and absorb water. In manufactured stone veneer, the entire system can be water permeable. Water absorption can occur through the stones and grout joints, and when there are no joints, the water passes directly through to the base coat.

Often, a thick enough base coat is not applied. This layer has limited water resistance and once saturated, the water then affects the secondary weather barrier. When no bond breaker is installed, asphalt felts, if used, can degrade and allow water infiltrating into the underlying building components.

These veneer systems are also more difficult to flash at roof–to–wall intersections than conventional masonry applications. Buric has observed gaps in construction that provide avenues for water intrusion. Where roof run–off water is mismanaged, water can penetrate to the cladding substrate. In some cases the stones are not well adhered and will dis-bond from the base coat, creating a potential fall hazard from the buildings. A number of other issues can occur with manufactured stone veneer.

What can be done to secure a problem-free future of manufactured stone in today’s construction?

Designers and applicators need to be aware of the construction limitations of manufactured stone veneers, as they failed to do with EIFS. This will continue to be a challenge to a housing industry in decline and where production builders often sacrifice details and building integrity for the bottom line.

As synthetic air/water barriers, liquid applied waterproofing membranes, and flashing systems continue to become more mainstream, they should help the cladding industry reduce its overall risk and help building owners enjoy the overall aesthetics of the product.

Buric advises its clients that when installing these types of claddings on buildings, they remain vigilant in observing all installation details and procedures. All wall claddings during installation and after completion should be closely monitored for signs of failure or distress. The more common types of signs that may become apparent for stone veneers are gaps, falling stones, staining, and cracks. As with all claddings, many factors determine the successful performance. For stone veneers, some of these factors are not readily apparent to the lay person and may require trained diagnosticians to determine the cause for problems that do become apparent. If you have a concern or are in need of more information on cladding, feel free to contact Buric’s Building Diagnostics service division.