In this session of Tile Q&A, I thought I would address two basic questions, whose answers may not be as basic as you may have thought. These questions and answers may bring about more comments on the subject. As always, feel free to send your questions to the e-mail address listed at the end of the article.
There are several things that can cause this. Typically the most common causes are as follows:
1) Excessive deflection in the substrate - this movement can cause the grout to crack, and if sufficiently severe, can cause tile to crack.