QUESTION

Can Efflorescence pass upward through a color through porcelain tile set over an interior concrete slab?

ANSWER

ANSWER - Efflorescence is generally a whitish stain caused by mineral precipitation.  Minerals within the concrete slab, the setting materials, and possibly the tile dissolve when subjected to moisture like salt in water.   The moisture then migrates to the surface taking the path of least resistance so it can evaporated as part of a drying process.

When the moisture evaporates the minerals precipitate leaving a a whitish substance.  It can cause spalling in some stones because as it precipitates it expands that can cause damage in the stone surface.

If the concrete and the color coating is porous then moisture can travel through it and carry the minerals.  The porcelain tile is impervious by definition so the moisture and efflorescence should not pass through it.  Although it can pass through the more porous grout joint, which is the path of least resistance in that assembly.