Hand-molded tiles need a varying amount of medium-bed thinset to account for each tile’s different thickness.

Plaster being applied over tiles that were thinset directly to the rough concrete swimming pool tank.
For thousands of years, ceramic tile has proven itself as an attractive and durable flooring material. In the United States, the tile industry has developed numerous materials, methods, and standards specifically for use with ceramic tile, and these may be found in the Handbook for Ceramic Tile Installation (the TCA Handbook), and in the American National Standard Specifications for the Installation of Ceramic Tile (the ANSI A108 specs).

Excess plaster being cleaned off a swimming pool tile.
Both are published and distributed by the Tile Council of America (TCA, 864-646-8453, tileusa.com), and although the methods and standards found in these two booklets were developed for ceramic tile, many of the same materials and techniques can be used to install other hard tiling materials that have some of the properties normally associated with ceramic tile.

The most common example of this is the installation of natural stone tiles. The Marble Institute of America references both the TCA Handbook and the ANSI A108 Standards, with changes and amendments that reflect the differences between ceramic and natural stone tiles. Ceramic tile is a uniform product manufactured to meet certain minimum performance levels, while the properties of most natural stone tiles vary considerably. For this reason, floors built for some stone tiles must meet a deflection standard that exceeds the L/360 required for ceramic tile:

installation materials and techniques are the same, but larger or more closely-spaced joists may be required. For ceramic tile, the industry minimums call for 10-inch joists, spaced 16 inches on-center, with unsupported spans no greater than 20 feet. Your stone supplier should be able to provide upgrade information for the stone tiles you need to install.

Another hard tile that may be able to use ceramic installation methods and materials is made from concrete, mortar, or a combination of the two. Terrazzo and molded concrete are two such examples. Concrete-type tiles can be made from Portland cement, synthetic resins, or combinations. Concrete or agglomerated tiles that are installed using ceramic tile installation technology should not be confused with other molded or pressed concrete blocks that are loose-laid without an adhesive. Concrete tiles may lack the precise manufacturing tolerances ascribed to ceramic tiles, but they are nevertheless used extensively and, within limits, can be installed using ceramic tile installation materials.

Lately, with the use of tile increasing, more and more materials are finding their way into tile installations. Glass, metal, and plastic tiles are now quite common, and designers are also adding beach glass and other recycled glass bits, metal castings and small metal industrial hardware, shells, beads, and other hard-surface materials as functional, decorative elements in floor and other tile installations. As on any flooring installation, durability, maintenance, and safety are major concerns. Metals may appear tough, but in a wet area, iron and steel tiling materials will rust and in the process, stain grout orange, and possibly expand and damage the grout; iron and steel expand slightly as they oxidize. The oxidation of copper, brass, or bronze tiling materials used in wet areas may impart a bright blue color unless the red-metal tiles are kept sealed. Stainless steel and Monel (a form of stainless steel) materials should not cause any oxidation-related staining or spalling.

I have mixed feelings about the use of plastic tiles on floor installations. There are a number of plastic tiles on the market, many of them mimicking the look of metal.

Finished tiles decorating a swimming pool.
Unfortunately, their metallic coating is usually only a few thousandths of an inch thick and prone to damage by abrasion. Metalized plastic tiles, unless otherwise specified by the manufacturer, should be used on wall installations only. Shells, beads, and marbles are often used as accents, but shells are notoriously soft and will wear out quickly under commercial foot traffic, in a food court, for example. Beads and marbles will also lose their original clarity and transparence, but until normal traffic hones off the slick sheen, these and other rounded objects including ball and roller bearings, pose a real safety hazard and should be used only for tiling walls.

Grinding installed sheets of rough-cut marble with a common belt sander to impart a smooth surface to the floor.
Consider any non-standard material as you would a ceramic tile, and ask common sense questions. Is it affected by exposure to water? Will it stain the surrounding tiles or structure? Is it capable of supporting intended loads and traffic? Is it tough and durable, and will it last at least as long as the other materials in the installation? Does it require any special maintenance?

Installing non-standard tiles

Aside from the usual structural, subflooring, surface-preparation, and tile-performance requirements, the first consideration for an installer working with non-ceramic tiles is the dimensions of the tiles. Are they dimensionally consistent like standard grade ceramic tile and need only to be bedded in a uniform layer of the right adhesive? Or are the tiling materials erratically sized, irregularly shaped, unusually heavy, or exhibit a deeply textured surface, and subsequently require individual treatment? Because ceramic tiles are so consistently sized, their installation can proceed quickly using production techniques. When dimensions vary beyond acceptable limits, though, labor and installation costs can quickly mount up.

The hollow backs of some three dimensional tiles (heavily sculpted trim shapes, for example) cannot support much weight and subsequently, should only be used on a wall installation. On a floor, hollow spots beneath any kind of tile can result in compression failure of the tile. There are two ways to fill irregular or hollow-backed tiles prior to installation: applying a thin layer of adhesive mortar to the exposed hollow, filling with a dry-pack mortar, and allowing the mortar fill to dry before the tiles are installed (the old, slow way), or filling the hollows and setting the tiles with a latex-based, medium-bed thinset mortar.

Glass bottle bottoms used as decorative tiles by the great Spanish architect Antonio Gaudi.
This method is faster since the filled tiles can be installed immediately. Regular thinset mortars are designed to be used in very thin layers-approximately 3/32-inch between the tile and the setting bed or underlayment-and should not be used in layers thicker than what is recommended by the manufacturer; otherwise, the strength and performance characteristics of the regular thinset are significantly reduced.

Unlike tile-setting epoxies whose rather runny consistencies makes them a poor choice for installing irregularly shaped, non-standard tiles, the consistency of latex thinset mortar can be site-adjusted (within manufacturer's limits), to fill hollows or support heavy tiles without settling, and the ability to install such tiles on an extra-thick bed of adhesive allows an installer additional leeway in smoothing a surface made of tiles whose surface may be less than the tile industry's definition of flat. Organic adhesives (mastics) should only be used in very thin cross-sections (probably less than 1/8-inch), and this makes them ineffective for use on many non-standard installations. Layers of mastic thicker than 1/8-inch may not dry sufficiently to provide enough compressive strength for the finished tiles: cracked grout and broken tiles are the result. Latex thinset mortars are available that can provide the needed strength quickly.

As with any other tile, materials used on a non-standard installation need to be adequately bedded in thinset mortar: 85 percent uniform adhesive coverage in dry, interior installations, and 95 percent in wet or exterior installations.

Polished brass accents inlaid into a black granite floor.
Experimenting with different notched trowel sizes is a must and some installers may use more than one size notch trowel to facilitate the installation. As well, some back buttering may be required to get all the tiles in a smooth, even plane.

During the installation process, use a damp sponge to clean off all excess mortar from the surface of the tiles, from the top third of the grout joint, and completely out of any grout joints designated as movement joints. If an installation has to be returned to service quickly, use a rapid-setting thinset mortar.

Grouting Non-Standard Tile

Some non-standard tiling materials are difficult to grout, and may require masking and other specialty grouting methods such as: waxing, the application of resists, piping, and other techniques. Waxing is often chosen for tiles that will be installed with Furan adhesive and joint filler. In practice, the wax is hot-washed off the tiles after the grout has cured making it a practical option only in the industrial or food-processing plants where Furan is usually found. For commercial and residential applications, installer-applied resists are readily available. If possible, and to ensure that the resist is compatible, select one made by the same manufacturer as the thinset and grout that will be used (single-sourcing is a key to trouble-free warranty servicing).

Resists must be applied carefully. Spraying is not recommended because overspray off the surface of the tiles can stick to the tile sides, where it is not readily cleanable and results in later problems when the stuff finally dissolves.

The gold glaze on these tiles inlaid into a black granite wall are so delicate, they need to be masked off before grouting.
Better to use a roller or brush to apply the resist (a liquid with a paint-like consistency) only to the surface of the tiles. There are resists that claim to be self-removing when the fresh grout is first cleaned off the tiles, but if the tiling material demands that a resist be used, I tend to select those that require a separate cleaning process to remove the resist after the grout has dried.

When grouting non-standard tiling materials, piping is sometimes used, after a resist has been applied, to eliminate time and labor-consuming wet cleaning normally associated with grouting. With piping, grout is loaded into a grout bag and forced through a nozzle directly-and only-into the joints. With patience, a careful installer can fill each grout joint completely without too much spilling out onto the surface of the tiles. The grout is then allowed to begin to firm and setup, at which point a smooth striking tool is used to compact the grout and squeeze excess grout out to the sides where it is left to dry further, and then removed with a soft brush. This method takes considerable installer skill without any savings in time over conventional grouting methods, but for highly textured surfaces or areas where wet cleaning is not desired, piping can significantly reduce the impact of traditional wet cleaning.

Timing is important when grouting any tile and essential when finishing non-standard materials. Cleaning before the grout has a chance to begin setting up results in too much grout being removed, and without much impact on the tiles. If the installer waits too long, though, removing even small amounts of excess grout may take its toll and abrade the surface of the tiling materials. Allow the grout to cure fully before removing any resist or applying any sealers or finishes.

As in all tile installations, the job is finished when the movement joints are filled with a flexible sealant or caulk that is color and texture-matched to the grout. The above guidelines should help with your non-standard tiling project; for specific advice regarding product selection and use, consult the manufacturer's specific instructions.