Bathroom mold, explained
Surface Spots or Something Behind the Tile in Your Jan Phyl Village Bathroom?
Every bathroom mold call falls into one of two buckets. Surface mold on grout and caulk lives on soap film and shower spray, and it scrubs off. The other kind grows behind the tile, inside the wall cavity or under the floor, where a failed shower pan, a leaking valve or a bad wax ring keeps the framing wet for months.
Silicone caulk is a common trap. When the growth is inside the bead, no spray will reach it; the old silicone gets sliced out with a razor, the gap is dried and treated, and new caulk goes in. Overhead, the ceiling above the shower collects condensation when the fan is too small, gets shut off right away, or blows into the attic rather than through an exterior cap.
Older tub surrounds often hide paper-faced drywall behind the tile, and paper is mold food once water gets past the grout. When the cause is a leak, the remediator and a plumber usually have to coordinate.