We have a tile shower stall with a fairly new pan (2-3 years, maybe). It leaks after some showers. We have access to the plumbing behind, and we've opened up areas below and at floor level behind and in hallway beside (where we see moisture after showers if it happens - doesn't take long, right after shower). (Also house is 1914, but shower is about 25 years old). Tile appears to be solid. Tile man who did some caulking for us knocked on it, etc. Said it was good - concreteboard backing looks OK where we can can see it (so not the obvious problems I've seen in other posts).
I tested as follows:
- ran hose directly from shower pipe to drain - 1/2 hour or so - nothing
- plugged drain and flooded pan 20 min-1/2 hour - nothing.
- hung plastic over right 2/3 (including plumbing fixtures below showerhead) - took a week + of showers by 2 of us - nothing
- shifted the plastic to cover only the right side, uncover plumbing fixtures - nothing after first shower, but some after my wife's shower. drain backing up both times to 1-2 inches depth (about what I flooded the pan).
Handyman says it may be failed grout after 25 years. Any other possibilities? What to do?