I’ve had leaking from my master bath bad enough that mold was growing on the ceiling beneath. The contractor ripped out the bottom two rows of tile and took out the shower stall pan. The plywood was blackened (I am assuming from the water leaks) along the edge of the main shower door). They reset the pan but didn’t remove or replace the blackened plywood underneath. I’ve also heard conflicting reports on whether there ought to have been anything installed under the shower stall pan (a membrane liner or sub floor). I have a basic fiberglass Mus-tee pan. I don’t feel that I really have an answer about what was causing the leak, and I do worry about mold and mildew as everyone in the family has bad asthma and allergies. I do appreciate your comments.
Yes, I understand your concern regarding the blackened and moldy plywood. My preference would have been to replace it if it was either compromised by wood rot or otherwise unstable. Without inspecting the plywood it is difficult for me to recommend immediate removal. But if you are concerned about air quality for that room, then you may want to invest in the purchase in a stand alone air purifier than can treat the bathroom area and most likely the adjoining room.
You are correct to bring the attention back to the underlying cause of the leak. It is somewhat troubling that plumber did not apparently locate this leak or provide an adequate explanation for why water was getting underneath the flooring. Though clearly, the area is always going to be subject to a certain degree of water drip-page. The important thing is to ensure all of the tiles are set correctly and the shower stall pan is adequately caulked.