CAUSES
1. It is possible to use large quantities (thickness over 2 cm) of glue. It is the basic principle that should not exceed the thickness of the tile. If there are altitudinal differences in the substrate, cut before setting the tiles with cement mortars (for small differences) or cement mortar for smoothing concrete (for large differences).
2. The "teeth" of the spatula with which the adhesive is unwound are large enough and sparse, resulting in the gap leaving it in the shell tends to be covered by the adhesive (as it tends to spread to fill the stress of the Uniform stress substrate) . In these cases a spatula with a smaller tooth spacing is used between them and without much depth. Sometimes there is "sinking" at the corners of the tiles when they create a "hip joint".
3. Sometimes due to the "hugging" that have some tablecloths (sorting or not) and not in the wrong application.
4. For large plates (60 x 60 cm and over), it is recommended to use thick glue, which can get thick but also withstand the weight of the tile without "sinking".