The second in a three-part series, Columnist Michael Byrne takes the next step in the process of installing Mexican Saltillo paver tiles.

In the ceramic tile industry, most manufacturers strive to create a product that is relatively easy to install over any surface that meets the minimum specifications found in the American National Standard Specifications for the Installation of Ceramic Tile (ANSI A108). And in a perfect world, those surfaces would always be in prime condition, flawless and ready for installation.

In the real world, however, an installer needs to be able to deliver a smooth floor over some less-than-perfect setting beds. Over slightly bumpy subfloors, installation can be a tedious process. And when the tiles themselves are neither flat nor true, as is the case with Saltillo Mexican paver tiles, it can tax the talents of even the most skillful installer.

Hand- or machine-grinding can eliminate lippage. Machine grinding tends to take away much of the allure of the hand-made look, but hand grinding, when applied sensibly, can improve the tile's look and durability, as well as help reduce maintenance. Grinding is really only practical with raw, unsealed, unstained tiles. Grinding pre-stained or sealed tiles can create a renovation headache when it comes time to match the stain for the ground areas with the rest of the tile.

Sorting the Tiles

As mentioned in the first installment of this series, sorting the tiles according to their degree of flatness is the first step in the installation process, and will determine the amount of grinding required. Step two involves rinsing each tile - front and back - with clean water, unless the tiles do not require cutting on a wet saw. This should be done just before the tiles are installed; however, all surface moisture must be absorbed by the tiles before they are set in adhesive. Any excess moisture should be wiped away or otherwise dried off before setting.

Choosing the Right Adhesive

Organic adhesives should not be used for setting non-flat tiles unless they are warranted for that purpose by the manufacturer. The best adhesive is a medium-bed latex or polymer-modified thinset mortar. Medium-bed adhesives can be built up in a rather thick layer without losing strength (regular thinset mortar loses strength as its thickness increases). Mexican paver tiles are usually quite porous. The use of latex additives or polymer-modified mortar and grout is highly recommended.

Notched trowel selection is very important - a 1/4-inch-by-1/4-inch square notched trowel is incapable of spreading enough mortar for Mexican pavers. A 1/2-inch-by-1/4-inch U-notch trowel is probably acceptable, but larger U-notches are recommended.

A thicker adhesive bed usually allows for more leveling of the tiles in relation to each other, as well as reducing the need for grinding.

Applying the Adhesive

Prior to the installation, pre-fill the backs of any domed tiles with thinset mortar and set them aside to dry. Whether applying the mortar to the back of a tile or to the surface of a setting bed, the process is the same: press a small amount into the surface with the smooth edge of the trowel, distribute additional mortar across the area to be covered, then establish a uniform layer with the notched side of the trowel. Many tiles will need additional mortar to achieve complete adhesive support.

Check frequently for sufficient mortar coverage. Gaps and voids can result in damaged tiles. The square-and-spot design shown here is a very old layout for floor tiles (Photo 1). The spot tiles can match or contrast the squares. Spots can also be made from seashells, marbles, metal castings, or almost any material not affected by foot traffic or water. Because of the difference in thickness, the spots shown here are supported with additional mortar (Photo 2).

Aligning the Tiles

Because of their dimensional irregularities, Mexican paver tiles are not installed with a rack, but rather with the help of a grid of layout lines. Because the grout lines for this pattern do not extend more than one square and one spot, a reference grid is used, along with a straightedge, to guide the tile placement. A conventional floor is usually installed with a 3-foot grid. As each grid square is set, the tiles should be leveled to each other with the help of a large beating block.

The block used for this project is a square of plywood, large enough to bridge at least two tiles (Photo 3). Using the block will speed the surface alignment of the tiles, but the key to good surface alignment is providing a cushion of mortar beneath the tiles. If too many tiles bottom out on the setting bed, it is because the notched trowel is too small to spread enough mortar for reasonable alignment.

Manufactured tiles, since they vary only slightly, are aligned with one edge set against a layout line. But with pavers, the tiles should be set so the layout lines run more or less down the center of the joints. Since the dimensions of hand-made tiles can vary dramatically, each tile should be set slightly off-center for the tiles to give the appearance of being lined up. This "relaxes" the installation. Lining up each paver's edge against a line can make the floor look contrived and stiff. Avoiding sharp edges, either in the layout or with individual cut tiles, is a major factor in finishing a Mexican paver floor.

Hand Grinding the Tiles

After the mortar has dried (usually 24 to 48 hours), examine the floor for lippage exceeding specification limits, which normally range from 1/8-inch to 1/4-inch or more (Note: there are no established limits for lippage in ANSI A108).

Use a set of hand stones - rough, medium and fine - to knock down the excess and soften the edges by holding the neighboring faces of each stone at a 45-degree angle to the setting bed (Photo 4). Use a masonry rubbing stone for rough work and an inexpensive sharpening stone for the fine stone (As an alternative, use 80-, 120-, and 200-grit carbide sandpaper). Run the rough stone back and forth along each joint to rough out the rounded edge, then finish with a fine stone to soften adjacent tile edges (Photo 5). More grinding will be needed for those tiles whose lippage is excessive (Photo 6). If neighboring tile edges are of equal height and slightly rounded, don't grind them at all.

I prefer to grind the edges of cut tiles after they have been set. This assures a smooth, flowing edge, which is especially important on the curve (Photo 7). Be sure to clean off any mortar on the surface or top edges of each tile. After the grinding and cleaning is finished, vacuum away the dust and wipe off the surface of the tiles with a tack cloth to prepare them for the sealer application. Wait at least 24 hours before applying the sealer, and then only after most of the moisture has evaporated from the tiles and adhesive.