The use of thin-set mortars have met the challenge of properly installing ceramic and porcelain tile for years, and still do today. Large-format tile in the past was 8” x 8” and was for the most part, installed using a 1/4” x 1/4” x 1/4” trowel. However the game has changed and continues to transform. Tiles have gotten larger, longer and proportionately have more inherent warpage.
Today’s popular larger tile sizes can be 6” x 36”, 1m x 1m or larger, and include an industry-standard allowable amount of warpage (where the center of the tile is higher than the edges or ends). In order to accommodate and support this high spot in the center of the tile, mortars needed to also adapt. What was formally known as a medium-bed mortar is now known as a large and heavy tile (LHT) mortar. Although these mortars do not yet have a standard established for the product or the installation method, one is on the way and should be in place in the near future.
LHT mortars allow the mortar to be spread with a thicker configuration than conventional thin-set mortars as seen in the attached photo. This additional amount of mortar, when troweled in a straight line pattern, is designed to support the ends of the tile fully as well as the center, which many times is higher. Without this needed support, the tile is very susceptible to breakage under a concentrated load such as a high heel, which can exert over 2,000 lbs. of pressure per square inch. Additionally, this lack of mortar or empty space can produce a hollow sound under normal foot traffic—which is not only unpleasant but most times unacceptable.
Even with these larger amounts of mortar being used, some ceramic tile products may necessitate the application of a skim coat of mortar on the back of the tile, commonly known as back-buttering. One additional note: all natural stone products require the use of back-buttering in every application. Using one or both of these techniques will normally meet or exceed the tile industry minimum standards of 80% mortar coverage on the back of tile in dry areas, with wet and exterior areas requiring 95% coverage.
The best and most effective way to confirm this minimum requirement has been met is to occasionally remove a tile. A good tile mechanic meeting the requirements of qualified labor, as recognized by the Tile Council of North America (TCNA), will use this procedure regularly to ensure the consumer is getting what they deserve: a high-quality, long-lasting, and trouble-free installation.
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