There was a time when I thought choosing tile meant deciding which colors would look best in the kitchen and bathrooms. People at the beach would explain that tile works well in a beach house in terms of cleaning but does of course scratch and is slippery when wet. Actually, both of those assessments can be true but are not necessarily true. Floor tile carries with it more than 4,000 years of technique, trial, error, and success so that the intricacies and varieties of choice and quality are nearly endless…and yes, there is tile that will not be scratched by sandy paws nor slipped on with wet feet. Each of these aspects is measurable by the Mohs scale of mineral hardness and the coefficient of friction for slip resistance.
The Mohs scale of mineral hardness was devised in 1812 by the German mineralogist Friedrich Mohs (1773-1839). Mohs selected ten minerals that were readily available and based the scale on their linear order of scratch resistance. Conveniently, Mohs’ name also works as an acronym for “measure of hardness scale,” making it easy to remember. The Mohs characterizes the scratch resistance of various minerals through the ability of a harder material to scratch a softer material. Minerals with small atoms, packed tightly together with strong covalent bonds throughout tend to be the hardest minerals. Qualities of hardness are generally consistent because the chemistry of minerals is generally consistent. A scratch on a mineral is actually a groove produced by micro fractures on the surface of the mineral. It requires either the breaking of bonds or the displacement of atoms. A mineral can only be scratched by a harder substance. A hard mineral can scratch a softer mineral, but a soft mineral can not scratch a harder mineral. Therefore, a relative scale can be established to account for the differences in hardness simply by seeing which mineral scratches another, which is the essence of Mohs’ work. The Mohs Hardness Scale starts with talc at 1 and ends with diamond at 10 and is universally used around the world as a way of distinguishing minerals. Simply put; the higher the number, the harder the mineral. This method is actually ancient, having first been mentioned by Theophrastus in his treatise On Stones in ca 300 BC, followed by Pliny the Elder in his Naturalis Historia, written about 77 A.D.
Understanding the hardness scale is important when selecting tile for a beach house, because sand (quartz) is 7 on the moths scale. If the tile has a higher Mohs than seven, it will not be scratched by sand on the floor…really, no matter how hard you try. There are now more sophisticated scales and methods of measuring hardness, but the Mohs remains a reasonable tool for basic applications. Most ceramic tile manufacturers use the Mohs scale to test the scratch and abrasion resistance of the glaze that is applied to the tile and / or the body of the tile. Tile hardness is affected both by materials used and by the firing process. The amount of alumina (aluminum oxide) in clay determines the hardness of the tile. Alumina occurs naturally in some clay, like kaolin, but can be added into other clays to produce a harder tile. During the firing process, a longer and hotter firing eliminates oxygen and slightly shrinks and condenses the tile, which is another factor in tile hardness.
Coefficient of friction is used to measure slipperiness or the lack thereof. The coefficient of friction is a measure of the amount of resistance that a surface exerts on substances moving over it, equal to the ratio between the maximal frictional force that the surface exerts and the force pushing the object toward the surface. The measurement is not always the same for objects that are motionless and objects that are in motion. Motionless objects often experience more friction than moving ones, requiring more force to put them in motion than to sustain them in motion. In other words, a grandson running across a slippery kitchen floor in socks is more likely to fall than the person standing washing dishes at the sink. The static COF is the measurement that applies to objects that are motionless. The kinetic or sliding coefficient of friction is the measure that applies to objects that are in motion. In a COF measurement, a higher number indicates a less slippery surface. A higher COF is created by adding insoluble crystalline materials within the glaze. Textures in the surface of the tile also increase slip resistance. In our house, because we can often have wet surfaces from wet people coming in and out, the tile floors all have a wet COF of about 0.6. We all know when a floor “looks” and “feels” slippery, which is another reasonable first cut at slip resistance.
The important thing to remember about tile hardness and coefficient of friction in household applications is that tile is created with intention to be used in certain areas with given sets of parameters. Wall tiles are not the same as floor tiles, and tiles for outside patios and pool areas should not be the same as those inside the house. Tile manufacturers have developed processes for longer and hotter firing and for adding materials that affect the final product’s performance and durability as well as its beauty. Even though a tile sales person may say that these factors are not important, they are. If in doubt, have a conversation with the technical support or engineering personnel at any given tile manufacturer. The contact information is readily available online.
Once the tile and design has been chosen, which grout and underlayment to use are the next choices to be made. Without question, the grout choice for us was an epoxy grout, rather than the old style cement grouts. We specifically chose Laticrete Spectra-lock, because it is non-staining, non-cracking, helps to prevent leaks between tiles, and doesn’t require sealing. Epoxy grout is more expensive and requires a skilled installer, but the overall addition to the cost is minimal compared to the results and the performance. It is important to keep the comparative cost in perspective as well, since the old style grouts are extremely cheap but require yearly sealing and frequent cleaning. There is definitely an overall cost increase for epoxy grout, but when considering the house costs across the board, the additional amount is minimal for a permanently beautiful and maintenance free floor. As a plus for the aesthetics, epoxy grout has a luster and depth of color that truly outshines the old grouts, especially with glass and stone tiles.
Because cracked ceramic tiles are difficult to repair, it is important to try to prevent cracking. The familiar underlayments like Durock and Hardi-backer do the job of supporting the tile, but they can't prevent shifting and cracking. Because the tile is adhered to that substrate and subject to stresses from building movement or uneven applications, shifting and cracks in both the tile and the old-style grouts will occur. A relatively new product offered by the Schluter company addresses the issues of underlayment using both historic and current data applications. Read this excerpt from the Schluter web-site to get the idea, and then take a look at this video to get the picture:
Ceramic and stone tiles are durable, easy to maintain, and hygienic, representing the ideal surface coverings. However, today's lightweight construction methods can make the installation of hard surface coverings particularly challenging. In order to protect the integrity of the tile assembly, an underlayment that performs multiple functions is required.
Schluter-DITRA is a polyethylene membrane with a grid structure of square cavities, each cut back in a dovetail configuration, and an anchoring fleece laminated to its underside. Schluter-DITRA is bonded to the substrate using thin-set mortar. The anchoring fleece on the underside of Schluter-DITRA is fully engaged in the mortar to provide a mechanical bond to the substrate. Tile is installed over Schluter-DITRA using the thin-bed method in such a way that the mortar becomes mechanically anchored in the square, cutback cavities of the Schluter-DITRA matting.
Designed specifically for ceramic tile and dimension stone installations, Schluter-DITRA serves as an uncoupling layer, waterproofing membrane, and vapor management layer that accommodates moisture from beneath the tile covering. Further, DITRA performs all these functions while still providing adequate support/load distribution for the tile covering. Tile has been successfully installed for thousands of years by incorporating an uncoupling layer, or forgiving shear interface, within the tile assembly. Schluter-DITRA provides uncoupling through its open rib structure, which allows for in-plane movement that effectively neutralizes the differential movement stresses between the substrate and the tile, thus eliminating the major cause of cracking and delaminating of the tiled surface.
Once all the key decisions have been made about the structural aspects of the tile, then the design process can begin. Great tile that has the perfect hardness and slip resistance, installed with epoxy grout and ditra underlayment can still look perfectly awful, so it is important to find a creative and experienced tile designer and installer to make the ideas work. Here on the Outer Banks, the best company to pull everything together is Creative Touch Tile. Pete Sandfort, the owner of the shop, loves tile in all its many varieties and applications. Pete has a wonderful ability to envision and enhance the ideas that his customers bring into the shop. Because he keeps up with the tile industry, Pete is excellent at offering suggestions and tangential ideas that make his designs unique in both style and energy. He’s also fun, and that is priceless! Because Pete has been in the tile business for a long time and has years of installation under his belt, he knows how to create designs that are intricate but also doable for the installer. Our house is very simple in style, so Pete’s challenge from us was to create something simple but beautiful, and we think he succeeded. Pete’s office manager, Kathy Lucia, adds her ebullient personality and knowledge to the choosing process.
In the end, the most important person in the process is the tile installer. If the installer isn’t meticulous and knowledgeable, the project will lose its appeal. Our tile installer, Brian de Pedro, who owns T and T Tile, has the experience and expertise for the job, and he works to make the job beautiful as well. Brian and Tom, another “tile guy” who works with Brian, did a nearly perfect job with our floors. Vince and I have other tile projects that we hope to add over the years. I hope these guys are around to make those ideas come to life when the time comes.
