Look at new construction in your community and you'll likely see more buildings clad in stone. Take a closer look, and you might find that thin stone veneer is becoming the material of choice on many projects. Contractors are choosing thin stone for a variety of reasons: its natural beauty, a sense of permanence, ease of installation and the ability to match existing stone structures economically.
In response to market demands, several companies are now involved in the development of panelized thin stone veneer products in addition to standard or custom-cut veneer. Panel dimensions vary and can range in size from 10- by 16-feet to more compact 1-square-foot pieces. These panelized systems, featured in two of the projects described in this article, give architects, designers and installers some new and attractive options when specifying natural stone.
New York's Fordham University now includes an architecturally appealing parking structure featuring Champlain Stone's Corinthian granite veneer.
Photo courtesy of Nicholas D. Lombardi, S.J.
Intermodal Transportation Facility, Fordham University
Located on the campus of Fordham University's Rose Hill campus in New York City, this five-story parking facility contains more than 1,500 parking spaces and provides shuttle services to and from the University, the Bronx Zoo, the New York Botanical Gardens, the Belmont-Arthur shopping district and the Metro North Rail Line. Its planning and construction were a combined effort of the University, city, state and federal governments.
The goal was to take this large parking garage and to construct it in such a way that it didn't look like a parking structure. "It was designed to blend with the campus context, the vocabulary of the campus," says architect Doug Hyde, who designed this structure during his tenure with Einhorn Yaffee Prescott Architecture & Engineering PC. "Fordham is a stone campus and this project embraced that idea." Hyde's solution was to gift wrap the structure in stone.
Corinthian granite from Champlain Stone was chosen to maintain continuity, primarily because this same variety of stone was used on the adjacent O'Hare Residence Hall, which Hyde also designed. "Corinthian granite was also used for the bridge that provides connectivity from the parking structure to the residence hall through a portal, which in essence is a major gateway to the campus," he says.
Installers put finishing touches on stone panels at Fordham University's parking facility.
Photo courtesy of Champlain Stone Ltd.
Full-size hand laid stone was originally considered by decision makers at Fordham, but was not a viable option in this case. "It was impossible to find real stone masons in New York City in sufficient numbers to economically execute a project of this scale," says Bryan J. Byrne, PhD, vice president for administration, Fordham University. "We learned this during the construction of O'Hare Hall. We tried to use another system of concrete molds with full-sized inlaid stone but the contractor defaulted."
Panelized walls with thin stone veneer attached to the surface were finally chosen as the best option. " The panels assured everything was going to stay together," says Erin Brothers, project coordinator for Champlain Stone. "Eastern Exterior Wall Systems spent a long time testing our stone, confirming it would hold using this method."
Hyde notes that these panelized walls ultimately achieved the same look as the hand laid stone used in the construction of O'Hare, without the amount of labor and equipment needed to perform this kind of work on-site. Also, the panelized systems cost less and create less debris on the construction site than full bed stone installation.
Construction detail of thin veneer panels being assembled at EEWS facility in Bethlehem, Pa.
Photo courtesy of Eastern Exterior Wall Systems
Panelization also allowed all of the stone work to be performed in a controlled manufacturing environment without weather delays. "After completing the panels required to enclose the building, our company can usually face a building of this size in six to eight weeks," says project manager Jeffrey Bartleson of Eastern Exterior Wall Systems.
Champlain Stone cut pieces of the Corinthian granite, achieving a desired thickness of 3/4 to 11/4 inches. "Then it became our responsibility to work the stone further, knocking off the perimeter arris and arranging the stone in the Ashlar pattern as seen on the finished panels," Bartleson says. "We first created a mock-up panel, which was approved by the architect, and used as our control sample for the remainder of the project to ensure consistency."
Prefabricated wall panels for this project were comprised of six-inch 16-gauge galvanized studs, sheathing, a 3/4 inch mud bed with lath, thinset and the Corinthian granite stone veneer. Panels were assembled in the Eastern Exterior Wall Systems manufacturing facility in Bethlehem, Pa. "The panels in this particular case had approximately a 10-day shop life cycle due to the amount of wet goods used," Bartleson says. "This is to say there was a lot of time spent curing."
The material needed to attach the panels in the field is usually independent from the panel itself. "In this particular case, the panels were attached using an assortment of shelf angles and 'T' bolts which were attached to the precast first and then welding the panels to the angles," Bartleson says. "Every panel connection is unique from project to project as panel sizes, weights and deflection criteria may change. Therefore all panel connections are engineered and are somewhat job specific."
A front view of the university's O'Hare Residence Hall reveals a close match to the parking facility.
Photo courtesy of Nicholas D. Lombardi, S.J.
By using the same ratio of small, medium and large stone in developing the pattern, consistency from panel to panel was maintained. After erection was completed, the 3/4 inch joints between the panels were eliminated using a color matched silicone caulk and backer rod. "It's nice to be able to offer architects and engineers an alternative means to the labor intensive process in applying field stone," he says.
Bartleson notes that this project was a very unique challenge for his company. Trying to mimic field-installed stone without compromising the overall look was difficult. "Having to compete with the restraints of the panel size rather than having a continuous wall canvas to work with posed an assortment of obstacles," he says. "It took some time to develop the system that we used in our shop for manufacturing these panels, but we eventually ironed out the flaws. I think the finished product speaks for itself."
Despite the large learning curve, it proved to be a very straightforward process — and the finished product met or exceeded expectations. "The goal was to build something attractive and lasting — something that's a part of the campus context instead of being just a big parking structure," Hyde says. Byrne agrees. "The garage has been well received both for its functionality and its aesthetic impact. The extra effort was worth it given its proximity to the main entrance to the campus."
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Moisture Drainage and Ventilation
Natural thin stone veneer installations are made of the same materials as any masonry wall. What installers are now realizing is that thin veneer installations also act much the same and that they need to take steps to avoid possible problems with moisture and toxic mold.
"If you look at all the documentation that the Brick Industry Association puts out for brick and stone wall construction, they always specify an air space — and the reason why is that moisture passes through masonry products," says Jim O'Neill, sales engineer for Keene Building Products. "Mortar absorbs water, and moisture works its way through masonry units to the other side. The problem is that in the majority of the walls that are built today with thin veneer, there is no air space. Weather resistant barriers become the sole prevention for leakage, something they were never designed to do."
Several products on the market provide that missing air space in thin stone applications. This does two things — it lets the weather-resistant building paper perform as it was designed by creating an air space on one side of it while providing an avenue for drainage and ventilation. Incidental moisture that is migrating through the wall has a place to exit the building without seeping inside because the weather resistant barrier is performing properly. It has a cavity that drains through the bottom to the exterior, as well as letting air circulate, providing drying on both sides of the wall.
According to O'Neill, the air space creates a capillary break. "There can be a terrific amount of moisture stored in these masonry walls. And if the masonry is touching the weather-resistant barrier without an air space, capillary action just keeps drawing it into the building," he says. "You provide an entangled net product like our Driwall Rainscreen behind the thin stone veneer, and it breaks up the capillary action."
In parts of the country that experience frequent freeze and thaw cycles, hairline cracks in the mortar joints can exacerbate the moisture problem. These hairline cracks allow wind-driven rain to penetrate the mortar and collect within the interior wall. "Moisture eventually gets in and of course causes mold and rot," says Kevin Lolley, sales manager for Advanced Building Products.
After installing their product, Mortairvent, a ventilation cavity is created between the vapor barrier and exterior wall. The polymer core mesh creates airspace, while the filter fabric blocks mortar droppings from seeping into this newly formed cavity — and still allows moisture to pass through. The combination of drainage and ventilation eliminates the threat of toxic mold.
When it comes to flashing for commercial projects, copper is the material of choice. "It's a little more expensive, but it's the only metal that's completely resistant to all the acids and alkalis that are present in fresh mortar," Lolley explains. "When you're building a school, court building or any of the commercial structures we deal with, you're talking about a 100-year structure, so you don't want flashing that's going to fail in 10 or 20 years."
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Columns at the Marriott are clad in Sierra Sandstone Shadowstone.
Photo courtesy of RealStone Systems
Marriot Facelift
The Minneapolis Marriott City Center Hotel originally featured a 1980's style interior that needed to be made more contemporary. "There were no program changes — it's just basically a philosophy of change that Marriott decided at the corporate level about the look and function they wanted in their hotel restaurants, bars and lobbies," according to designer Byron Kermeen from Walsh Bishop Associates. "The existing interior at this location didn't fit the model."
Stone was chosen as the new interior wall covering. According to Kermeen, the use of stone was a nod toward Minnesota's Northwoods. For cost reasons, a RealStone System thinstone veneer product was chosen. Cladding the columns in stone was about one-third the cost of wood.
RealStone System's Sierra Sandstone Shadowstone, a variety of quartzite, was specified by the architects at Aumiller Youngquist PC and Walsh Bishop Associates to renovate the lobby, restaurant and bar. Minnesota Brick & Tile, a RealStone Systems distributor, supplied approximately 3,000 square feet of stone for the project. "Sierra Sandstone Shadowstone continues to be one of our more popular products used in both the commercial and residential markets in a wide variety of applications for interiors and exteriors," explains Mike Ryan, national marketing manager for RealStone Systems.
About 3,000 square feet of stone were used in the Marriott renovation.
Photo courtesy of RealStone Systems
The veneer material used comes as a 6- by 24-inch panel of dry stack ledgestone, which is composed of individual stone veneer pieces stacked and adhered together to form standardized one-square-foot panels. Grout or mortar between the panels is not necessary. A tolerance level of +/- 2mm on the panels greatly reduces any visible gapping once installed.
Panels come preassembled and are ready to install right out of the box. Each piece on average weighs 10 pounds, so it still only takes one person to set up. Like conventional thin stone veneer, once the surface is prepared, installers mortar the back of the stone and stick it to the wall. Installers typically start from the bottom up to make sure everything is level. "Installation is roughly 25 percent to 40 percent faster than typical natural thin stone veneer," Ryan says. "The installer is able to put up a square foot at a time versus smaller individual pieces."
More renovations are planned for the structure, and Kermeen says they are advocating the continued replacement of existing wood with thin stone veneer. "It will be continuing up on the sixth floor where there is an open atrium," he explains. "The stone will be carried forward in the renovation."
RealStone panels merge together to form a 90 degree corner with ease.
Photos courtesy of RealStone Systems
John Brown University Restoration
At the heart of the John Brown University (JBU) campus in Siloam Springs, Ark., stand three gothic-style buildings known as the Cathedral Group: the Cathedral of the Ozarks, the Engineering Building and the Art Building. They are the focal point of the campus. All were originally built of concrete block with concrete openings and trim.
Since the construction of these structures in the 1940s and 1950s, sun, rain, ice, and sleet have taken their toll on the exposed concrete block causing significant staining, crumbling and other deterioration. The deteriorating integrity of the concrete block put the interiors of these buildings at risk for moisture penetration and mold.
JBU began a restoration and renovation campaign to face all the buildings with limestone veneer — using limestone was actually part of the original building plans. In addition, the project includes roof replacement, restoration of stained glass windows and updates to the interiors. The project goals were to restore, preserve and extend the lives of these buildings.
Using limestone was part of the original building plan for the restoration project at JBU.
Photo courtesy of U.S. Stone Industries
"That kind of architecture was very unusual in a block building from the '50s," says Kent Barnow, managing partner of U.S. Stone Industries. "It's a great case study of what's possible, even with buildings in that condition."
More than 30,000 square feet of Kansas Cottonwood sawn split-face thin veneer was utilized in the renovation. "It was sawn to specific lengths and heights, so it wasn't random," Barnow says. "The cut stone was fabricated in two standard sizes and profiles."
According to Eric McBride, president of John McBride Construction, some of the block had deteriorated over the years, which had been patched with Portland lime mix. "We covered that with some paper backed lath," he says. "The limestone was installed like typical veneer, putting on the ground coat and then the stone in an Ashlar pattern." Veneer to cover the concrete openings and trim were thinned down by sawing them to size at the site.
The project started in early July 2007, and the bulk of the project was completed after seven months. JBU raised the $6.1 million total cost, with $1 million matching grants from both the Mabee Foundation and the Kresge Foundation.
The Cathedral of the Ozarks in Arkansas has a bright new look thanks to limestone veneer facing.
Photo courtesy of U.S. Stone Industries
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Sticking With the Right Variety of Mortar
Thin stone veneer is always the star of the show, but what about the supporting cast? Unfortunately, mortar selection is not always given proper consideration in planning for construction projects. Choosing mortar is just as important as choosing the thin stone veneer itself — mortar accounts for up to 17 percent of the wall's visible surface and is the "glue" that holds the stone in place.
"Installers should choose some type of modified mortar, either a latex or a polymer acrylic to enhance the stickiness and lessen the amount of sag," says Stan Harwell, mid-Atlantic and northeast sales manager for Amerimix. Sag refers to the tendency of the stone to slide down the wall or shift position as a result of its weight.
Temperature differences are also a consideration. "If you're putting the backing or setting mortar against a cold concrete block wall, you're probably going to want to add some kind of accelerator, and you'll want to heat the water to increase mortar temperature," Harwell says. "In the summertime, when it's hot and the sun is beating down on a block wall with no moisture in it, you're going to want an additive to hold the water in longer."
Installation in northern climates is affected by seasonal temperature extremes. "You're going to want mortar with good entrained air content in the 8 percent to 12 percent range," he explains. "That's going to help with freeze-thaw issues." Harwell also suggests that installers consider the extensibility of the mortar ?how much will it shrink in relation to the backing material. "You can get hazing and cracking behind it, which opens up the possibility of water penetration."
Most pre-blend companies, including Amerimix, have a product made especially for thin stone veneer. "You don't need a lot of strength in this application; what you need is good bonding capabilities and good flexural strength," Harwell explains.
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More than 30,000 square feet of Kansas Cottonwood sawn split-face veneer was utilized in the renovation of the Cathedral Group on Arkansas' JBU campus.
Photo courtesy of U.S. Stone Industries
Mark Haverstock is a freelance writer in Boardman, Ohio. He has published more than 500 magazine articles on a variety of topics.