The method you're referring to is called "scratch-coat" or "Jersey-Mud Job". It's not an approved method of setting floor tiles, but it's done every day. It has a high failure rate, but probably works well long term 70-80% of the time. That is not good.
The method has been tested by the TCNA and TTMAC, the Canadian equivalent, and has failed every time. Why is it used so much in Canada? It's cheaper to do, so tile setters who use it don't want to do a better job and lose jobs and money.
Tell us more about your tile project.
TILE GUY - retired- TROY, MI - Method & Product suitability consulting.