Thinset mortars were developed many years ago to replace the necessity of "wet setting" tile on mortar beds. With the inclusion of products like methycellulose together with portland cement and aggregate, the inventor could bond tile to substrates in a very thin application of the new found mortar. This revolutionized the tile setting industry allowing tile to be set on substrates like concrete slabs without the use of a conventional mortar bed.

Here is the problem, some folks want to use thinsets like a traditional mortar bed when they apply them in thicknesses exceeding 1/4 inch. That seems to be simple until the class of thinset mortars came around later called "medium bed" mortars claiming working thickness up to 3/4". Even these mortars are susceptible to excess shrinkage when used at their thickest recommendations.

Here is the key, keep thinsets as thin as possible never any less than 3/32 inch nor greater than 1/4 inch wherever possible. Never use any thinset to level the work of others. Before applying thinset mortars, have the substrate on-plane within 1/4 inch in 10 feet for ceramic and 1/8 inch in 10 feet for stone.

That will allow the user to keep the setting beds uniformly thin and problems at a minimum!