Stone Tile Selection

The author used a set of copper patterns to produce these radially cut floor tiles from 12x12 Midnight Black granite.

The 12”x12” slate used to tile this exterior BBQ were rated for exterior use by the dealer. The curving edge of the countertop was roughed and finished on-site.

Historians tell us that flat stones were probably the very first paving material to be used by man to enhance his living environment. Such stones have been identified and even dated to thousands and thousands of years ago, and largely because of its perceived strength, stone is often the first material that comes to mind when we think of durable, long-lasting performance. Unfortunately, strength and durability are properties that are not an inherent part of all stone used for tiling. If you have ever visited the Parthenon in Greece or the Pyramids in Mexico or Egypt, that last sentence may be hard to accept since the world is full of architectural treasures made from stone or decorated with stone tiles and mosaics.

Until about 50 years ago, most stone tiles came from quarries that had operated for hundreds or even thousands of years. These quarries were discovered and developed long before national or international standards, precision measuring equipment, or reliable test labs. Properties of stone were determined the hard way through trial, error, and experience. Over time, a history of use revealed any shortcomings of a particular stone, and as quarries supplying unusable materials were abandoned, quarries supplying good stone gradually accumulated catalogs of successful projects that were used to help sell the strength of their products. With this approach, precise measurement of properties was far less important than a stone’s ability to perform in a variety of environments such as: dry tropical (high heat), wet tropical (high heat and humidity and frequent rainfall), light-, moderate-, or hard-freezing (freeze/thaw cycles), continually submerged in water, and so on. As you might imagine, most of the history of the use of stone tiles involves big-budget projects for significant state or religious buildings.

While dry disc sets are available for on-site touchups and repairs, the author prefers to use wet discs for grinding, profiling, and polishing stone tiles.

Today, hundreds, if not thousands of different stone tiles are available, many at amazingly low cost. But with a price tag at under a dollar a square foot for some offerings, the first thing an installer should see is a red flag. I have personally installed beautiful-but-soft slate 12x12s purchased for $.79 from a big-box retailer. The beautiful color exhibited by these tiles, caused by a very thin layer of minerals, overcame the concerns we had for the material: some of the tiles appeared ready to delaminate, the color layer was soft and easily abraded, and no information regarding performance testing or physical properties was available. Even worse, the retailer sold the goods as is: no refunds or adjustments for any reason. For that reason, I purchased 50% more than was required to cover the floor so I could pick and choose the best tiles. Together with careful installation that included a perimeter movement joint, and very gentle grouting, the end product resulted in a gorgeous floor. Now into its seventh year, the half-bath floor still looks great, but there has been a noticeable dulling of the colors. Nevertheless, the client loves the floor, which has acquired a lovely patina and appears to be original to the 60-year old house.

That installation, using suspect tiles, only persists because the half-bath is very low use, and has never been subject to harsh cleaning methods. For an active household, though, those somewhat fragile tiles would be a mistake. How is an installer to know what to use and what to avoid? The first step is to understand that the fundamental difference between ceramic and stone tiles is that the properties of ceramic tiles are fixed by a combination of: ingredients for producing the tile body and tile glazes, how the ingredients are converted into a tile shape, how long the raw tiles are fired in a kiln, and how hot the kiln is fired. By altering the recipe, ceramic tiles exhibiting a wide variety of properties can be produced accurately and consistently. On the other hand, the properties exhibited by most stone tiles is expected to vary within the blocks quarried for stone, within any given batch of the same stone tiles, and within an individual tile.

To demonstrate how easily lippage can be entirely eliminated on this relatively soft honed marble mosaic floor, the author uses a carpenter’s belt sander to smooth the surface of the tiles prior to grouting.

There are 19 properties and associated testing related to ceramic tiles. There are also about the same number of similar properties and industry-recognized testing for structural stone. To go over each of the properties would take far longer than space in this article (and reader patience) allows, but the bottom line for me is that when comparing ceramic and stone tiles, or when I have to determine the properties of a stone tile, best results come when the stone tiles are examined according to tests established for ceramic tile – not for structural stone. I base my prejudice on the fact that the properties of a particular stone – and its performance in the real world - may change as a thick block is sliced into thin tiles. That said, I may approve or disapprove a selection based on existing results from testing developed for dimensional stone, but when a project calls for the performance testing of a stone tile, I prefer to send samples to the Tile Council of North America (TCNA) Lab for examination by tests developed for ceramic tile.

As well, in spite of positive test results, unknown and unforeseen properties of stone may affect performance and durability. For this reason, while tests may confirm that a certain stone tile is suitable for an intended use, I prefer to use a selection method that avoids any shortcomings with testing. The method is relatively simple, but I use it to quickly determine suitability. Simply put, I ask the supplier to provide the location of a similar installation using the same tile I am considering. Claims of suitability often vanish once that question is asked, and whether the project is multi-million commercial or a simple household floor, it is always the first question I ask.

Many installers learn the hard way about stone tile installation, and often give up on stone after their first major problem, but to the installer who wants a challenging creative outlet, and a more profitable business, stone tiles present many opportunities. If you have an interest in installing stone tiles, I recommend membership in the Marble Institute of America (MIA) as an informative first step. MIA is a gateway to materials, methods, and techniques, and their Dimensional Stone Design Manual should be in every serious installer’s technical library. Armed with this knowledge, a profile wheel and a set of grinding and polishing pads, many installers have seen their interest grow into a full-time business.

Selecting the right stone tile is only the first step. Most stone tile floors require a stiffer structure than what is acceptable for ceramic tiles: make certain that the structure you want to tile meets the tile supplier’s requirements for deflection. Be especially careful of any structure that requires a crack isolation membrane system for the safe installation of the stone tiles selected for your project. Finally, since there are a number of bonding issues with stone tiles, don’t try to economize by selecting sub-par installation materials.

Author’s Note:In the interest of full disclosure, lest some readers think I am biased against stone or stone tiles, my wife and I absolutely love our wildly colorful Blue Louise granite kitchen, and with the exception of my wife’s tiles, or book projects using ceramic or porcelain, I have only worked with stone tiles since moving back to the west coast about 10 years ago. My 1995 Vermont HBA Best Bathroom Award featured several varieties of stone tiles.

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