The traditional way: back-buttering and beating inTraditional mortars, which are typically formulated for tile up to about 12 inches square, maintain their rigidity very well -- too well, in fact, to be effective for tile beyond that size. When using these setting materials for larger tile, installers face two challenges.
First, they must back-butter the tile with mortar, an extra step that is necessary to ensure complete mortar coverage on the back of the tile and proper bonding to the substrate. Second, when setting the tile in the mortar bed, a tremendous amount of pressure (â€œbeating inâ€) is required to smooth out the ridges and create a good bond. The average maximum pressure that an installer is able to apply to a tile is about 30 pounds. While this is adequate for tile up to about 12 inches, it will require nearly two and a half times this force to set an 18- x 18-inch tile. If the pressure is insufficient, the ridges do not smooth together, and coverage is not adequate, leaving air pockets under the tiles. They will sound hollow and are at risk for popping up.
Since these larger tiles must span larger areas, the imperfections in the floor must be bridged between the tile and the floor. Therefore, more pressure is needed to assure that the tile contacts the mortar in the low areas of the floor. Many problem cases result in a call-back to remove the tile and re-install with additional mortar (assuming the tile has not cracked or broken as a result).
More effective with less effortEurope is where the larger-tile trend began, so it is no coincidence that new advances in polymer chemistry began in Europe as well. While manufacturers of tile installation products have been creating polymer-modified thinset mortars for years, this new technology is very specific to the needs of larger-format tile. Called â€œflowableâ€ mortars in Europe, the new polymer chemistry has now come to the U.S. These new polymers impart a fluid quality that is still rigid enough to support the use of deeper-notch trowels, yet reacts to pressure by allowing the trowel ridges to flow easily together and spread out to the edges of the tile. This eliminates the need for back-buttering entirely, and greatly reduces the physical application of pressure needed to set the larger-format tile.
Perhaps most important is the fact that these newly formulated thinset mortars return to a â€œrestâ€ state once the pressure is removed. These thinset mortars will support the tile rather than allow them to settle into the mortar bed. This â€œsettlingâ€ associated with older mortars had been responsible for uneven edges, or â€œlippageâ€ (as would be the case with an over-watered, conventional thinset mortar). Fortunately, the new mortars return to their original state of rigidity -- a characteristic that allows for accurate setting and a level, even finished surface. The new mortars can level out irregular concrete substrates, filling gaps to eliminate highs and lows.
Some manufacturers are also offering â€œrapid-settingâ€ versions of these new mortars. Ideal for commercial venues such as restaurants, hotels and shopping centers, these formulas cure quickly with high early strength and can accommodate traffic in as little as 24 hours.
As the trend of larger-sized tile continues to rise, there is no doubt that tile professionals will appreciate new mortar technology that saves labor and speeds the installation process.