1.Why can’t we use only cement mortar for tiles now, but must use glue?

The tiles in the past, more accurately called tiles, had a water absorption rate of more than 10%. Before putting them on the wall. They would be soaked in water to fully absorb water, and then paved with cement mortar. Because the water content was sufficient, and the combination with cement mortar would be more in place, and the bonding force between the two would naturally not be bad.
Moreover, the size of tiles at that time was relatively small, mostly 300×600, and the pressure on the wall was relatively small. Today’s tiles are getting bigger and bigger, and 600×1200 tiles are not uncommon. Moreover, not only are they large, but their water absorption rate is also very low. For example, vitrified tiles,
through-body tiles, etc., the water absorption rate can be controlled at about 0.5%.
This leads to the fact that if only cement mortar is used. It is difficult to bond perfectly with tiles. In order to solve these problems, products such as tile back glue and tile adhesive appear.

2. Why are there more hollows and falling off after applying glue?

The widespread use of large bricks on the wall has made hollows and falling off more even if the “glue” paving process is used. To figure out this problem, we must first understand what kind of glue is used for the wall tiles now?
There are probably two types:
① Tile glue is actually cement in essence. It is just an upgraded cement. In addition to cement being the preferred choice, the sand in it has also been upgraded to quartz sand. Adding some additional auxiliary materials, the bonding strength is much stronger than ordinary cement. It can be called a super substitute for cement mortar
② Tile back glue is essentially acrylic emulsion. That is, glue, which is a kind of interface agent. Generally, a layer is applied on the back of the tile to enhance the bonding strength with the tile glue.
Nowadays, for the sake of safety, both decoration companies and workers will recommend using tile glue + tile back glue together. But the facts have proved that after applying, hollows and falling off have not been fundamentally solved. Why is this?
HPMC for Tile Adhesive