i'm seeking a profesional answer regarding tiles work(theoryticaly). in our country, we use to place tiles after two layers of other materials that are- 1. cement, 2. sand layer, 3. tiles adhesive mixture, 4. tiles. the question is step 2, i don't know what to call in profesional but i call it sand layer which is a mixture of cement (1part) and sand (5-6part) lay between (after)the cement concrete layer and (before) tiles adhesive mivture. i did the reserch, no such answer is in logic, somesay for shock absorbtion, more sticky etc. but as i known there is no such layer in westen countries. so i jump to conclusion that may be they want to cut thier cost for getting a stronger layer of concrete or the consumption of cement (my point of view). i'm in mechanical background, please give me some civil answer. i thank you, thanks.