marble shower caulking issue
we re-did our bathroom last yr, we had customized shower pan made from marble tiles, and shower wall is marble slab. We had a decent licensed contractor doing the job and it passed all the inspections. One issue keeps coming up w/shower caulking. We re-applied the caulking a few times, for some reason, the old white caulk BEHIND the (sealed) gray caulk, is still getting wet/damp somehow, and breaking the gray caulk? It happened even after removed all the bad caulk, and dry things out w/ denatured alcohol & hot air, and re-seal w/ new caulk.
No idea how this could happend.
would it just be condenstation/moisture from the regular air, in the wall, onto the back of marble? or some wicking through the marble walls, or grout? (we do squeegee dry the shower walls and floors, most every time...)
Thx for any input!