The useful answer starts with timing and pathway
Water management depends on the concealed waterproofing, penetrations and drain connection rather than the tile face alone.
Best first comparison
Document when the symptom begins, what condition preceded it and where the first visible or measurable change occurs.
Before deciding on a repair
Compare at least one credible alternative cause and choose a check that can separate the two without creating new damage.
Observe→Compare triggers→Repair source→Verify outcome
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