This defect is a straight crack or twisted crack that runs through several adjacent surface tiles. In most cases, such cracking of the tile is not accompanied by its separation (even incipient) from the lower layer. In very rare cases, when such a defect is formed when tapping, an empty sound is present, characteristic of a violation of the adhesion of the tile and the base. However, very often, such cracks not only pass through the entire thickness of the tile, but also affect the lower layers, especially the base and the supporting cement layer.
The defect is mainly of an aesthetic nature, which becomes more serious in the case of using glazed tiles, since the formation of such cracks can be accompanied by cracking and destruction of the glaze. Even though such cracks often have a physiological effect, that is, one should worry about the condition of the floor or wall, the functionality of the facing surface is almost never called into question. In this case, as in the case of failure of fastening and sagging of floors, the defect is caused by various loads acting on the facing layer (more precisely on the tile and base), which exceed the mechanical stability of the tile. These loads are transferred from the load-bearing layer.
Cause
In most cases, such a defect occurs when two circumstances are present simultaneously. The first of these is an extremely strong (in terms of adhesion) but rigid base. Substrates with such characteristics include cement-lime mortars with particularly high cement content and adhesive mortars with short shrinkage and hardening times. And the second is the presence of 1) an easily deformable structure, that is, a structure capable of withstanding significant pressure in several directions (by the way, cracks often form along these directions), or 2) a structure with some degree of mobility or capable of yielding to loads along certain lines, or 3) a structure under pressure caused by shrinkage of solutions during the solidification process or temperature fluctuations, opposed to external and internal connections between the cracks of the structure (such cracks appear on the surface in accordance with the cracks of the structure itself).
In any case, the formation of such a defect occurs as a result of errors made at the planning and design stage. To establish whether this defect is a consequence of a defect in the structure itself, it is necessary to obtain various data on all components of the system, which is very difficult to do. Let's give a few examples. There are known pathologies associated with 1) structural joints that were not taken into account during cladding, 2) incorrect positioning of the supporting structure (for example, the use of concrete without taking into account shrinkage/bending joints, which can cause the formation of cracks), and 3) poor insulation of technical systems (wiring, pipeline and the like). Planning and design errors in this case lie in the construction of an overly rigid double layer of base tiles (using closed joints), which is not able to withstand deformations (that is, without well-placed and calibrated expansion joints), and/or excessive interaction with the lower layers ( that is, without installing separating layers). In most cases, the formation of a defect does not depend on the work performed.
Prevention
In this case, the measures necessary to avoid damage to the fastening and sagging of the floors are applicable. The occurrence of a defect is directly related to the loads acting on the facing surface from the lower layers. These loads can be controlled by appropriate design decisions such as the use of open joints, the use of adhesives with appropriate elastic and plastic properties, careful planning of expansion joints, and the intelligent use of techniques that will reduce stiffness, for example, floating floors.