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Exterior Applications As appeared in Schluter-Systems The Profile Newsletter Elegant, durable, and easy to maintain, ceramic tile and natural stone are ideal for producing claddings in exterior applications where UV-rays, moisture, and thermal influences are present. Advances in tile manufacturing technology have provided us with a large variety of frost-proof ceramic tiles that can easily withstand these environmental influences.

Mother Nature has made an even greater contribution by offering an array of natural stones in a virtually limitless selection of textures, colors, and minerals. It’s easy to understand, then, why more and more architects, designers, and homeowners are choosing ceramic tile and natural stone for exterior applications.

Since frost-proof ceramic tile and natural stone can easily last forever and the demand for these materials is increasing, how can we take advantage of the considerable potential that exterior applications offer the industry? The key is proper installation!

Renovation of this four-story residence, situated on California beach frontage, included the addition of Portuguese limestone as exterior cladding.

Let’s take a look at a renovation project in Corona del Mar, California where 3,000 sq. ft. of Portuguese limestone (24" x 24" x ½") were installed as exterior cladding on a four-story residential dwelling. Situated on beach frontage, the exterior is constantly exposed to salt, moisture, and wind, placing exceptional demands on the installation. The planning and forethought of the architect and contractor resulted in an installation system worthy of the tile and capable of withstanding these climatic conditions.

On this particular project, the limestone was to be installed over a brown-coat, which is typically used as the base for a traditional stucco exterior. It was decided, however, that prior to the installation of the limestone, a waterproofing membrane be installed over the brown-coat to prevent the intrusion of salt and moisture into the assembly. Although this procedure addressed the issue of salt and moisture, it created yet another concern: How do you deal with the residual moisture that becomes trapped between the moisture barrier beneath the brown-coat and the waterproofing layer now placed on top of the brown-coat?

There were other things to consider as well; for example, the build-up of stresses within the assembly. Since ceramic tile and natural stone are rigid, brittle materials, bonding them directly (force-conductive bond) to the substrate, whose coefficient of expansion and contraction is intrinsically different than that of the tile or stone, would result in the transfer of stresses and, ultimately, cracking and de-bonding of the stone cladding.

To overcome the resultant dynamics of the assembly and the physical demands placed on the installation by the environment, it became evident that the waterproofing membrane would have to perform three functions. It would have to (1) waterproof the vertical wall assembly; (2) uncouple the tile covering from the substrate so that the two could move independently of each other, thus preventing the transfer of stresses from the substrate to the covering; and (3) accommodate the residual moisture trapped between the moisture barrier and the waterproofing layer.

Designed specifically to address these types of installation concerns, Schluter-DITRA matting provided the ultimate solution. DITRA’s unique ability to uncouple the finished surface from the substrate addressed a key concern by isolating the stresses created between the substrate and the stone due to thermal changes, gravity, etc. DITRA, in conjunction with the surface covering, would also act as a waterproofing membrane, thus protecting the substrate from any penetrating moisture. Additionally, the air channels beneath the DITRA would allow for evaporation of residual moisture within the brown-coat. The ability to accommodate moisture occurring within the brown-coat would allow the tile-setting to begin soon after the brown-coat was applied. Without the DITRA, the contractor would have had to wait the required 28 days for the brown-coat to cure before tile-setting could begin.

Air channels beneath Schluter-DITRA allow for evaporation of residual moisture within the brown-coat.

The installation proved to be quite simple. The DITRA matting was applied to the brown-coat using thin-set mortar. Schluter-KERDI-BAND was then used to seam the DITRA to all inside and outside corners and connections to eves, windows, and doorframes. Because the installation was on the vertical, stainless steel fasteners were screwed into the studs with 1½" washers approximately every 16 inches on center, in each direction, securing the DITRA to the structure. The stone was installed over the DITRA using a latex/acrylic medium-bed mortar. Finally, rather than grouting the stone, every joint was filled with exterior-rated elastomeric sealant. This included all tile transitions to windows, doors, and eve joints.

Although this method was not required for use with the DITRA matting, it was chosen to increase the water-tightness of the installation. Also, this procedure was well within the Tile Council of America’s recommendations for movement and control joint frequency!

Schluter-DITRA was designed to serve as an uncoupling layer for problematic substrates, a waterproofing layer, and a vapor pressure equalization layer to accommodate moisture occurring at the underside of the substrate. It is easy to see how the intrinsic characteristics of this matting matched perfectly the needs of the Corona del Mar project. In fact, this project provides the design/installation paradigm for the new millennium, allowing us to take advantage of the true potential that exterior installations offer the industry.