Architectural Record BE - Building Enclosure

Large-Size Porcelain Slabs for Building Surfaces

Interiors and exteriors finished with half-inch slabs can create lightweight and beautiful results
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Sponsored by Walker Zanger
By Peter J. Arsenault, FAIA, NCARB, LEED AP

Exterior Building Applications

While interior applications of large porcelain slabs are commonly thought of, exterior applications on building facades are a logical and attractive choice too. Panel-type building facades have been common for decades and often include wood or steel framing for the structural support, plus a supported finished panel as the exterior weathering surface. Large porcelain slabs can easily replace stone panels or other panels, thus creating a lightweight but durable surface, coming in at about 5.5 pounds per square foot. With the range of colors and patterns available, they can be used to replicate wood, stone, or smooth surfaces in a consistent pattern across a facade or with contrast and variety built in. Further, with the growth in the need for continuous insulation in exterior wall assemblies to comply with energy codes, porcelain slabs can readily cover the face of continuous insulation, creating a full cladding surface.

The key to successfully using porcelain slabs for the outermost surface for any exterior wall assembly is the method of attaching or securing them in place. In some cases, adhering the tile to an appropriate wall sheathing or backer board on the exterior wall may be appropriate for residential or light commercial buildings. The joints would then be grouted with an appropriate watertight grout and sealed if needed. Checking with manufacturers and following specific recommendations and guidelines for the adhesive and grout used will be important here to assure proper installation and durability. Also checking for guidelines on height will be important; a slab placed above another may need some additional support to avoid creep and movement over time.

For commercial installations, a common approach for panelized facades is to use an aluminum support system of vertical and/or horizontal channels or tees that are secured to the building structure with adjustable aluminum clip angles. Porcelain slabs can be set into such a support system that carries the weight and wind load of the slabs, transferring directly to the building structure. The depth and spacing of the clips and channels can be designed to allow for continuous insulation to be installed between them and satisfy thermal envelope requirements.

Porecelain slabs installed with consealed mounting in an office. Porecelain slabs installed in the kitchen.

Large porcelain slabs can be used on interior and exterior walls and installed with concealed mounting, allowing the exposed face of the porcelain to be the only visible component.

When it comes to attaching the panels to the support system, there are several common methods of attachment that can be used. In the simplest form, panels can be attached using adhesives to create a chemical bond between the panel and the support system. Instead of adhering to the substrate, as may be done for residential systems, porcelain slabs can be adhered to the aluminum support system based on tested and certified adhesive materials and techniques. One of the visual benefits of this approach is that, since the anchoring is done completely on the back side of the slabs, the joints are the only thing seen on the face. From a performance standpoint, this type of mounting uses the continuous nature of the adhesive anchoring to distribute stress evenly, preventing any concentration of stress in the adhesion surface and minimizing critical points where ruptures could begin. Further, the nonconductive properties of such anchoring enables the connection of different types of materials and prevents galvanic corrosion.

In some cases, it is desirable to have a full mechanical support system that wraps over the edges of the panels with exposed clips or clamps. Such systems have been developed for facades by a number of different manufacturers based on using aluminum trim type of profiles that attach to the support system. Visually, the aluminum trim can be a minimal profile that simply secures the slabs in place or a pronounced profile that adds shadow lines and reveals to the facade. In doing so, the popular building facade design approach of using a ventilated rainscreen system can be considered. In this case, the facade is based on the principle of separating the exterior cladding from the rest of the wall assembly. A space between them is intentionally designed to allow for air to enter and ventilate the wall as well as allow any water that enters to drain out of the bottom and away. The idea is that the cladding is the first line of defense against the weather but allows for air and water to enter a small space behind it. The surface of the substrate wall is treated to provide the full and continuous air and water seal and is protected by the cladding, in this case, the porcelain slab.

For tall buildings subjected to higher wind loading, ventilated rainscreens need to be looked at a bit closer. Higher wind loads mean more pressure is applied to the exterior cladding, and that can cause problems either to the cladding or the systems behind it. The solution is a pressure-equalized rainscreen that relies on creating smaller compartments across a facade rather than one continuous ventilation cavity. These ventilation compartments respond independently to constantly changing wind pressure. When wind-driven air enters openings in the bottom of the rainscreen and finds no way to exit, the air pressure inside the cavity matches the wind’s pressure and “pushes back” against it, preventing wind-driven rain from entering. If a small amount of rain is driven into the cavity, the same openings allow the water to drain.

In addition to the main facade cladding material, porcelain slabs can be considered for trim, accent, soffits, and other feature areas of a building. The selected textures, patterns, or colors can be precut or cut in the field using common tile-cutting techniques to create simple or ornate exterior designs.

Fabrication and Installation

Regardless of how the porcelain slabs are being used, it is important to fabricate and install them according to industry standards and in accordance with manufacturers’ recommendations and instructions for specific application. In all cases, the large sizes available help reduce installation time, thus saving labor costs, but proper workmanship and appropriate attention to detail is needed as with any finish material. It is also worth noting that field fabrication is possible with results that can rival factory precision for mitred edges and other details. This can be particularly important for custom items, such as countertops and stairs.

Illustration if fabrication instructions.

Illustrated fabrication instructions are commonly available from porcelain slab manufacturers and should be followed carefully for best results.

When porcelain slabs are being fabricated with cutouts or custom shaping, then water-cooled bridge saws or waterjet machines are called for, as with most porcelain and ceramic tile work. Commonly for saws, a 400-millimeter segmented blade spinning at 1,600 RPM and advancing on the order of 36 inches per minute is the norm, with water feeding directly onto the spot where the blade contacts the slab. Before fabrication starts, it is advisable to trim approximately ¾ inch from each of the slab’s four edges to remove any possible tension stress that may be within the slab. For all cuts, it is also recommended that the beginning and finishing portion (approximately 7 inches along either end of the cut line) be done 50 percent slower or 18 inches per minute. For 45-degree-angle cuts, the feed rate should be reduced to 24 inches per minute.

For cutouts, it is recommended that at least 2 inches of porcelain remain between the edge and the cut out to retain the integrity of the slab edge. Use of a drill for the corners will help assure precise fabricating. Within a cut out, the main body of the opening should be cut and removed first, leaving approximately 3 inches to be cut separately in a more controlled manner.

When installing the porcelain slabs using an adhered method, flooring installations and some small-sized applications could be installed with thin-set or regular-set adhesive common to many porcelain installations. However, for wall applications, whether interior or exterior, some manufacturers recommend a two-part epoxy adhesive due to the potential for the material to creep or slide down vertically. If a backer board is being used, it can be adhered or otherwise fastened to the structure or supporting layer first and then the epoxy applied between the porcelain slab and the backer board. In all cases, the installer needs to assure a 100 percent bond with no air pockets or voids that could allow breakage. If there are any details about the fabrication or installation that need clarification, then it is best to consult the manufacturer since it has probably encountered the situation before.

 

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Originally published in Architectural Record

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