Installing marble tile
Marble tile is prized for its beauty.
Marble tile is prized for its beauty. Calcium carbonate-based and made primarily of calcite crystals, marble features pronounced veining and naturally deep and sometimes bold colors. However, the mineralogical makeup of marble is also what makes installing marble tile tricky.
All marble is vulnerable to abrasion and chemical attack. Abrasion can be caused by grit and dirt on the soles of shoes, cutting utensils on bare countertop slabs, and other spills and accidents. Chemical damage is caused by spills, including lemon juice, tomatoes, vinegar and chemical cleaners.
Installing marble tile requires careful attention to detail. Using the wrong adhesive can bleed through to the surface and stain the marble tile, and rough handling can cause chips or abrasions. Once installed, marble should be treated with an impregnating sealer regularly to enhance the surface sheen and help safeguard against stains.
When installing marble tile, start with a smooth, flat substrate
Most tile installations require a substrate that is flat, smooth and free of divots, defects or bumps. This is especially true with marble. Marble’s natural veins are natural weak spots that can crack if the tiled is installed over a gap in the substrate.
Sand any raised areas and fill dips with floor filler. Larger areas of deflection (low spots) should be filled with self-leveling floor compound.
Spreading thinset and laying tiles
Thinset mortar can be applied directly to an exterior-grade plywood subfloor, but many installers opt to install cement backer board to stiffen the entire subfloor assembly and provide an extra measure of moisture resistance.
To ensure veining and color patterns match over the entire marble installation, do a dry run by laying out all the tiles before applying thinset or adhesive and have the customer approve the result. Also, make sure all tiles or slabs you purchase for a particular job come from the same original batch.
Usually when installing marble tile, you want to start in the center of the room and work outward. Find the center of the area and mark reference lines with chalk or temporarily attach a guide board to hold your first line of tiles.
Thinset mortar can be applied directly to an exterior-grade plywood subfloor, but many installers opt to install cement backer board to stiffen the entire subfloor assembly and provide an extra measure of moisture resistance.
For most installations using tiles 12-inches square or smaller, spread the thinset with a ¼-inch by ¼-inch square-notched trowel. Larger tiles or those that are irregularly tumbled or have pronounced natural clefts may require a ½-inch by ½-inch square-notched trowel for proper adhesion. Make sure the thinset is sticky to the touch and not too dry – it should be about the consistency of toothpaste. Use thinset specifically formulated for marble, and immediately clean any thinset that may spill or drop onto the tile’s surface or ooze up into the grout joints.
When installing marble tile, use a rubber mallet to gently tap the marble. Use a delicate touch, as marble can crack easily. Refrain from wiggling or moving the tile too much after it has been embedded in the thinset, as that can produce cracking along the natural veins.
Marble tile requires a wet saw to cool the blade as it cuts. Move the material slowly and deliberately through the blade when cutting. It is very easy to crack or completely shatter an entire tile – even when making small cuts.
Seal, grout, and seal again
Once the thinset has fully cured per manufacturer specifications, apply a high-quality sealer to the tile surface. This will help prevent staining during the grout application.
Mix grout in small batches that can be applied within about 20 minutes. Use your grout float to scrape away as much of the excess grout as you can after forcing it into the joints. Let the remainder form into a haze, and then clean it off as you would for any tile installation, using a sponge and plenty of clean water. Then mix another small batch of grout and repeat the process until done.
Apply at least one more coat of sealer after the grout has fully cured and the floor has been cleaned. Many pros will apply at least two coats of sealer at this point, letting each coat dry thoroughly before applying the next.
Marble floor tiles should not be walked on for at least 48 hours after installation.
