Recently, our most common floor installations have consisted of large tile that looks a lot like wood planks. More than once, we’ve gotten funny looks from people who were sure that they were looking at a wood floor. At almost 3 feet long and close to 6 inches wide, these tiles have the same basic shape as a board. But this shape brings with it the challenges of installing large-format tile. The Tile Council of North America defines large format as having any edge 15 inches or longer. Because of the size, the chances of lippage (uneven tile edges) or cracking after installation are much greater. For this reason, the TCNA has put out guidelines specific to installing large-format tile.
A Flat Subfloor Is A Must
For a successful installation of large-format floor tile, the most important factor is the flatness of the subfloor. In addition to its strict rules about deflection, the TCNA recommends that the subfloor have no more than 1/8-inch variation in 10 feet—tight tolerances for any subfloor. For this project, I made sure the plywood subfloor was within the TCNA tolerances before I installed a Ditra Mat uncoupling membrane over it.
If the surface of the subfloor had varied by more than 1/8 inch, I would have considered using a poured floor leveler on the worst areas—or on the entire floor—before installing the uncoupling membrane. The only area of this subfloor that was slightly out of level was in a hallway off the main floor. Because the hallway was relatively small (less than 10 square feet), I opted to use a mechanical “leveling” system there, which I describe later in the article. After installing the membrane, I rechecked the floor for flatness by trying to slide a silver dollar (which is just under 1/8 inch thick) under an 8-foot straightedge.
A flat subfloor is crucial because large-format tiles are seldom perfectly flat. During firing and glazing of a long, narrow strip of clay, some minor distortion can be expected. If two tiles with a 1/16‑inch bend are installed side by side, the middle of one tile can be 1/8 inch higher than the end of the other—the lippage that was mentioned earlier. An out-of-level floor will compound the problem. As I unpack the boxes, I randomly check the tiles for any major discrepancies, setting aside the worst tiles to be cut for shorter pieces.
Before I mix any thinset, I scan the room to determine which sides are the most visible. That’s where I’ll begin my layout. In this case, I decided to start at the front wall of the house and the wall adjacent to the front door. To keep the installation neat and easy to handle, I always put down just a few courses at a time. To minimize lippage, I stagger the ends; for this floor, I started with a quarter of a tile, then a half tile, then a three-quarter tile, and finally, a full tile. With four starter pieces, I worked four courses at a time.
To determine the layout, I set four tiles side by side, leaving 1/8‑inch gaps between them for grout lines. I measured 23 1/2 inches across the tiles; that measurement would guide my layout lines as the courses progressed across the floor.
The TCNA recommends leaving a 1/4-inch gap around the perimeter of the tile floor for expansion, so for the first section, I measured out 23 7/8 inches from the wall. Using a laser tool, I projected a straight line across the room and drew a line with a waterproof marker. Then I was ready to install the tile.
Photos by Roe Osborn