Why it happens: Usually because the subfloor is uneven or the underlayment is wrong. If the subfloor is uneven, or has too much “give,” it leaves room for the rigid tile to crack and shift.
How the pros do it: They test to make sure the subfloor is level, then secure it to the floor joists, and then (this is crucial) install the appropriate underlayment for your specific tile type, such as a liquid one in the case of concrete or porcelain tile. Your tile supplier can help you figure that out. The key is to do it. It helps cushion against any unevenness that may happen as you use the floor.
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