Installation of stone floors

Be sure to use unmodified thinset, as the latex-modified kind won't harden properly when sandwiched between the tile and the membrane. Starting in a corner, roll out the membrane, flocked-side down, beside the room's long wall. At the end wall, crease the roll into the corner, as shown, and cut along that crease with a utility knife. Trim as needed to get around pipes, ducts, and doorways. Lay out and cut the remaining sections so that their edges butt together and they cover the entire floor.

Number the sections, set them aside, then vacuum the floor. Mix a batch of thinset: Use polymer-modified thinset on plywood and unmodified thinset on cement-based substrates. Don't let the thinset sit—any delay could prevent a good bond. Butt the first membrane section into the corner and immediately roll it out onto the fresh thinset.

Spread and comb out another 6-foot section of thinset, and unroll the next portion of the membrane onto it. Repeat until the first roll reaches the end wall. Immediately after the membrane is laid, use a grout float to press every square inch firmly into the thinset, as shown. Do the same after laying each remaining section. Once the entire floor is covered, dry-lay a line of tiles between each pair of walls to judge how best to minimize cuts and get a pleasing layout.

Pick a starting point that will keep you from stepping on stones after they're laid. Spread unmodified thinset over an area about 3 feet by 16 inches, filling the membrane's square dimples. Comb out parallel ridges with the notched trowel.

For each tile, smear thinset on its underside, press it firmly in place, and make sure it's flush with its neighbors and that the joints are even. Gently remove excess thinset from the joints with a putty knife, and swab the stones with a damp sponge. The next day, wash away thinset residue with muriatic acid, and, to protect the stone from grout stains, apply a sealer. When that's dry, mix up a sanded grout and push it diagonally into the joints with a grout float.

Wait 10 minutes, then wipe off grout residue from the stone with a damp sponge, rinsing it often. Don't disturb the joints. The next day, rub off any haze with cheesecloth and wipe on a final sealer coat. The main reason this poor choice is promoted comes from the desire to have the stone tile floor installed flush to the adjacent floor finish. While this is a nice idea as far as the flush surface goes, it is really a recipe for failure for the stone tile. The TCNA Handbook has only one approved method for the installation of natural stone tile over wood framing with backer board.

These recommendations are based on the natural stone having adequate compressive strength, flexural strength, and resistance to abrasion, but be aware that some stone tiles may not be appropriate for floor use. The wood framed floor system must be in conformance with the applicable building codes prior to the natural stone installation. This means that the stone tile floor structure must be twice as rigid stiff as the wood floor system required for a ceramic tile installation.

Additionally, the Natural Stone Institute formerly the Marble Institute of America and the Building Stone Institute prohibits installations of stone tile over single-layer wood floor systems under backer board since the joints between the subfloor panels cannot provide the necessary strength. Therefore, two layers of structural wood panel are required on floors to receive stone tile when backer board will be used as the substrate.

When it comes to achieving acceptable mortar coverage, you're looking to meet the ANSI A requirement:. This information, when put into practice, will yield better results without costly callbacks and failures.

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