Home Archive Tile/Stone Talk: Exterior Adhered Veneer
Home Archive Tile/Stone Talk: Exterior Adhered Veneer

Tile/Stone Talk: Exterior Adhered Veneer

By Gregory Mowat, Forensic Tile Consultants


Exterior installations require an understanding of tile, masonry and code requirements for working with adhered veneer. Exterior veneer, including the backing, needs to provide a weatherproof covering. Additionally, the exterior wall envelope should be designed and constructed in such a manner as to prevent water accumulation within the tile assembly.

According to the International Building Code, adhered veneer is secured and supported through adhesion to an approved bonding material applied over an approved backing. Adhered veneer and its backing shall be designed to have a bond to the supporting element sufficient to withstand a shearing stress of 50 psi (350kPa).

Exterior veneer shall not be attached to wood frame construction at a point of more than 30 feet (9.1 m) in height above the non-combustible foundation; this limit may be increased when special construction is designed to provide for differential movement and when approved by the building official.

Special construction means using a metal-stud assembly, masonry, poured-in-place or tilt-up concrete for veneer above 30 feet in height. Sprinkling of the building may be required for veneer installed above this height.

Exterior veneer 2Consideration shall be given for differential movement of supports, including that caused by temperature changes, shrinkage, creep and deflection. The height and length of veneered areas shall be unlimited except as required to control expansion and contraction of the 30 foot height limitation for wood framed construction.

Adhered veneer units shall not exceed 36 inches (914 mm) in the greatest dimension or more than 720 square inches (0.46 m squared) in total area and shall not weigh more than 15 pounds per square foot (psf) (73 kg/m squared) unless approved by the building official. However, veneer units weighing less than 3 pounds per square foot shall not be limited in dimension or area.

Definitions in the International Building Code and referenced standards:

A number of different materials up to 1 1/4 inch thick may be installed as adhered veneer, like split brick, but coordination may be necessary for the support of heavier pieces of tile until a bond is established. Other common products treated as adhered veneer include thin-brick tiles; additionally granite, limestone, marble, quartz-based stone, and slate tiles not exceeding 1/2 inch or 5/8 inch (13 to 16 mm) thick are usually treated as adhered veneer.

Exterior wall assemblies can include wood framing, metal framing, tilt up concrete, poured in place concrete and concrete masonry units. When tile and masonry installers install tile, thin brick, stone tile and special purpose tile on exterior wall assemblies, water-resistive barrier paper, a waterproof membrane or vapor retarder may be required. Where tile is directly bonded to the waterproof membrane, the waterproof membrane must meet ANSI A118.10 requirements and be recommended by the waterproof membrane manufacturer.

Exterior veneer 3Installation of scratch coat includes the fastening of 2.5 pounds per square yard or 3.4 pounds per square yard diamond wire lath to the backing as a setting bed. Horizontal (cap of wall) may require stainless steel expanded metal lath. The setting bed shall be a minimum of 3/8 inch (10mm) thick and a maximum of 3/4 inch (19 mm) thick.

Successful installations include achieving a minimum of 95% contact and coverage of thin-set mortar, as well as the coordination of layout and location of the movement joints (expansion joints).

Apply mortar with the flat side of the trowel over an area no greater than can be covered with the tile before the mortar skins over. While using a notched trowel of the type recommended by the mortar manufacturer, comb the mortar to obtain an even setting bed without scraping the backing material. Cover the surface uniformly with no bare spots and with sufficient mortar to ensure a minimum 3/32 inch (2.4 mm) between the tile and backing after the tile has been beaten into place. Tile shall not be applied to skinned-over mortar.

For tiles with uneven thickness, a box screed may be used to true up deviations from plane between the tile units. The resulting thickness of mortar in back of the units shall not be less than 1/2 inch (12 mm) or more than 1 1/4 inches.

Tilt up concrete, poured in place concrete and concrete masonry units may require scarification of the surface to remove curing compounds or contaminants in order to allow water penetration so the thin-set mortar can properly adhere.

Using any other backing surface than those listed above, including exterior ceramic tile panel systems and cementitious backer units, requires approval through The ICC evaluation service. The Ceramic Tile Institute of Northern California has cautioned against using cementitious backer units as part of an adhered ceramic tile exterior veneer.

Bostik PanelTack installationWhile the requirement for grout between tile units is not included in the building code or tile industry requirements, a lack of grout may contribute to additional moisture penetration into the wall assembly. However, dry stack stone is commonly installed without grout.

California requires all veneer to be a minimum 1/2 inch (13mm) or thicker when adhered veneer is to be installed above doors at hospitals and schools. Where an Installation will be subjected to freeze/thaw cycles, degradation can occur over time. Where installation will be subject to seismic movement, special attention should be made to placement and width of movement joints.

Tile mortar manufacturers are recommending ANSI A118.15 LHT mortar for exterior adhered veneer installation of tiles without resins on the back of the tile. Installation of special purpose tiles may require chemical adhesion. Verify with the special purpose tile distributor, manufacturer/quarry or mortar manufacturer any special installation instructions and whether the tile is recommended for installation on exterior veneer. Caution is urged against using quartz-based stones or type C and type D marbles in areas where frequent wet/dry cycling will occur.

Special purpose tiles include thin-brick tiles, porcelain tiles, thin porcelain tile panels, flagstone tiles, granite tiles, limestone tiles, marble tiles, onyx tiles, quartz-based stone tiles, sandstone tiles, soapstone tiles, slate tiles, bluestone tiles, brownstone tiles, Mexican pavers, Saltillo pavers, Smalti mosaic tiles, agglomerated tiles made from the quarry waste of natural stones, terrazzo tiles, Catalan pavers, Cantera pavers, Adoquin pavers, concrete tiles either extruded or poured/layered, glass tiles, metal tiles, plastic tiles, wood tiles and simulated stone tiles.

Tiles with epoxy or polyester as components or on the backs of the tiles should be set with epoxy unless the tiles are submitted to an adhesive manufacturer with written installation directions supplied by the adhesive/mortar manufacturer. Another option exists in grinding the epoxy or polyester resins off the back of the stone tile in order to bond with a polymer-modified mortar.

Portland cement thin-set will not bond to epoxy, polyester, resins, paint, or mastic. Epoxy will bond to Portland cement, epoxy, polyester, resins or mastic. Moisture-sensitive stones may need to be set with epoxy.

For large area stone tile veneer installations, verify the color range expected. Blending of stone tiles may need to be specified where the shade range is normal and expected. Pre-sealing may be necessary when grouting over tiles that may absorb the grout. For the application of any sealers, follow the sealer manufacturer’s installations explicitly. All stones are not equal.

Always work toward successful installations!

How Madonna University’s Welcome Center was Slated

Madonna University Welcome Center 1There’s a new building in Livonia, Michigan, which is rigidly steeped in Christian humanistic values and deftly clad with one of the most ancient, time-tested of natural materials. Madonna University’s overall mission is to instill its students with intellectual inquiry, a respect for diversity…and a commitment to serving others through a liberal arts education based upon the truth. The overall design of the Madonna University Welcome Center was inspired by these values.

According to Matthew Teismann, AIA, NCARB, president/cfo at MKC Architects of Columbus, Ohio, “The Madonna University Welcome Center invites all people to visit a contemporary structure offering two mindsets. One being a location which provides a first view for incoming students; the other being a museum exhibiting history of the Felician Sisters of North America.” This second entity consists of a 4,300-sq. ft wing, named the Felician Sisters of North America Heritage Center and Archives. It celebrates the Felician Sisters — an apostolic congregation of religious women founded in the mid-1800s.

Madonna University Welcome Center 2Teismann described how the building’s interior theme embodies an updated version of “cloister design,” dating back to the basilica of Saint Francis of Assisi in Italy. “This five-year project was challenging,” he stated, “as we were tasked to come up with a contemporary building emanating historic significance. One way we were able to accomplish that theme was by specifying CupaClad natural slate to clad the exterior of the Welcome Center.”

The architects initially planned to clad the façade of this 30,550 square foot structure with black stone…but could not find material with the performance characteristics they were seeking. From there, they considered selecting various types of porcelain material…after that, black brick. “We ultimately decided upon CupaClad due to its contemporary, clean lines and also because this unique building material was historically significant. We also were pleasantly surprised when we were presented with CupaClad’s proposal, which indicated how cost-efficient it was, especially for higher-end buildings.”

Madonna University Welcome Center 3The architect added that final specification of this natural slate product was not only based upon it being affordable, but also being exceptionally durable and offering incredibly low maintenance, as well.

CupaClad’s Vanguard 201 was the product selected for the Welcome Center. Modern and efficient, this system marries large-format slates with stainless steel clips, creating a clean, contemporary combination. “Selecting Vanguard 201 ultimately results in someone seeing the building via a larger perspective,” stated Teismann. “People can now perceive how the exterior was installed via the grids and clips, which is actually a nice ‘look’…especially when considering the horizontally-formatted, large-scale blue slate modules by CupaClad. Also, to a more trained eye, because of the unique application method, the natural slate does not show expansion joints, which can break up an aesthetically rhythmic placement of exterior cladding.”

“This building was not intended to be a religious edifice,” concluded Teismann. “But even though it’s not religious in stature, overall, it is inherently very spiritual. CupaClad materials actually embody this.”

Photos of Madonna University Welcome Center courtesy of photographer Laszlo Regos, laszlo@laszlofoto.com


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