How many layers of materials were under the tiles?

4 layers of material

Explanation:

A long time ago the typoe of construction that used tiles, such as moisacs required a lot of concentration and work. One of the most important things was to choose the wall, then cover the wall with resin and after that they had to put 3 layers of plaster all over the wall, finally they used to put pieces of colored glasses (tiles) and the process was over.