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Unread 03-15-2021, 09:35 PM   #10
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Join Date: Jul 2001
Location: Boerne, Texas
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Pete, the ceramic tile industry no longer recognizes anything called "Medium Set" or "Medium Bed" mortars. They were, and remain, mortars used in the thinset method of setting tiles. It was confusing having those terms in past as it let folks to believe there was such a thing as a medium-bed method of tile setting. It's all use in the thinset method.

The industry does now recognize "Large and Heavy Tile" mortars (formerly Medium Bed). They were primarily designed to prevent such tiles settling on floor applications after they were set. Most are thixotrophic as recognized in the T designation with their ANSI standard number.

The greater/less than 15 inches on a side is a rather arbitrary designation in my view and the recommendation for the use of the LHT mortars at that break point should be tempered by the user/specifier of the particular tiles at hand. There is a good deal of difference in setting a 4x16-inch tile and your 12x24-inch tile, but both would fall under the LHT recommendation if taken literally.

If your tiles are flat and your substrate is flat, you may not need anything other than a regular A118.1 or .4 mortar, but the LHT mortar might still help. But that's:

My opinion; worth price charged.

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