The reason for the appearance of craquelure is either a difference in the coefficient of thermal expansion of the shard and the glaze, or deformation of the tile due to the impact of mechanical load on it. The listed factors lead to the fact that the glaze, due to its small thickness, cracks, while the body of the tile remains intact. This defect can appear immediately after the end of the production cycle (in this case they speak of “immediate craquelure”) or some time after laying the tiles (in this case they speak of “late craquelure”). Glazed tiles with an "immediate crackle effect" are considered defective, although sometimes manufacturers deliberately create collections of tiles with a "craquelure effect" for aesthetic purposes. “Late craquelure” occurs under the influence of the external environment during operation. The reasons for its appearance are:
- Thermal shock . Sudden change in ambient temperature.
- Insufficient drying of the cement base . A certain time is required for the solution to harden (crystallization of cement), dry (relative humidity equilibrium), and then obtain dimensional stability (end of shrinkage) of the cement-sand base. Failure to comply with this time interval will lead to the fact that the cement screed under the cladding will shrink, which may result in an uneven load on the tile.
- Excessive cement content in the interlayer . This is typical when laying tiles on cement-sand mortar. The increased cement content contributes to significant shrinkage of the adhesive composition.
- Excessive thickness of the mortar layer . Significant fluctuations in the thickness of the layer, due to unevenness of the base or the use of an unsuitable tool for applying the adhesive, result in its uneven shrinkage.
"Late craquelure" is a sign that the tile is deteriorating. The consequences can be quite serious, including cracking of the tiles.