Larger tile sizes are being used with increasing frequency on both walls and floors. While 12-inch tiles were once the standard for large format tiles, 18-inch tiles and larger are being found more frequently. These larger tiles provide a more open appearance with fewer grout lines than smaller tiles, but they also come with some installation considerations. While there are not many differences between installing a 12-inch and an 18-inch tile, there may be a few.
Lippage is the condition when a corner of a tile sticks up slightly above the rest of the tile, or the tile next to it. It is caused when a heavy tile sinks too deeply and unevenly into its mortar bed. The center of the tile frequently sinks lower than its corners, causing a small lip in one end. This problem may be barely noticeable, or it may be a hazard to walk over. Due to the increased size of large format tiles, including those sized 18 inches, lippage is much more common than in tiles sized 12 inches or smaller. To avoid this, 18-inch tiles must be pounded equally into the mortar bed using a soft mallet.
The larger a tile becomes, the more crucial that the surface below it is completely level without dips, humps or valleys. Grout joints, which decrease in number as tile sizes become larger, help a tile to flex over a valley or uneven area in the floor. An 18-inch tile has significantly less expansion or flex than a 12-inch tile will, which means that if the floor is out of level, an 18-inch tile is more likely to crack than a 12-inch tile is. Additional care must be taken to ensure an even substrate before installing an 18-inch tile floor. Use a self-leveling agent to smooth out the substrate before tiling.
Porcelain and ceramic floor tiles must be fired to extremely high temperatures during their manufacturing process. The height of these temperatures may cause some tile warping, resulting in an uneven shape or wavy backside of the tile. The larger the tile, the greater the degree of warping that can occur. For 18-inch porcelain and ceramic tiles, as well as some more fragile stone tiles, back buttering is required. Lay the mortar bed for the tiles, then place additional mortar onto the backs of each individual tile. This will even out any warping and help achieve a more even installation.
Weight and Thickness
Many 18-inch tiles are up to 1/2-inch in thickness, while the standard thickness for 12-inch tiles is 3/8 inch. This additional thickness, combined with the additional size of the tile, increases the weight of the tiles and therefore the weight of the installation. This may mean that the substrate must be checked to ensure it can handle the additional load of the tiles. Fast bonding thin sets and surface supports may also be required for the installation of 18-inch tiles on the walls to ensure the tiles remain in place while the mortar is drying. Typically lighter 12-inch tiles do not necessarily require these added steps. The difference in thickness between the tile sizes also dictates the types of cutting tools to use. A standard ceramic tile bit on a rotary tool effectively cuts thin tile but requires a change to a diamond wheel for cutting 1/2-inch thick tile.