Water damage in the ceiling below a second-story shower usually stems from one of two issues: cracked tile grout or a completely ruptured waterproof shower pan liner.
The Definitive Shower Standpipe Test
- Remove the shower drain grate.
- Insert an inflatable mechanical test plug into the drain throat below the weep holes and expand it tightly.
- Fill the shower basin with water until it reaches 1 inch below the threshold curb.
- Mark the water line with a pencil and leave it for 2 to 4 hours without running the showerhead.
If the water level drops, the waterproof vinyl or hot-mop shower pan liner is breached. If the level stays solid, the leak is caused by cracked wall tile grout or a leaking shower valve cartridge behind the wall.