We bought our house in Fresno, CA new in 2004. After about 4-5 years we noticed the upstairs master shower was leaking as evidenced by damage to ceiling in room directly below it. We contacted the home builder for repair work (in California they warranty all new construction for 10 years by law). Their general maintenance crew did a shower pan test that showed the shower was leaking at the corner where the glass door meets the wall and door well. The glass door has a gutter that runs all the water that falls on the door to this corner. After inspecting the corner we noticed the grout line was cracked, likely from the new house settling. It was unclear if the pan was not installed correctly or if the leak was high enough to get around the pan. The home builder, in consult with the tile subcontractor, decided to clean the grout line and lay new grout. This was done and they then placed a hardy amount of silicone over the repair for good measure. Fast forward another 5 years and the problem has returned but much worse, now I am out of the warranty period and want to repair it myself. I am good at general construction and tile work but have never installed or repaired a shower pan. I removed the glass door framing to get at the grout line and found the silicone they applied during the fix had mostly pealed up and was covered with black mold on the underside. I used a razor blade to remove the old grout which was also dark gray in color and very “rubbery” in texture, no longer tan and hard like this grout usually is. I fear the mold grew up from under the tile and thru the grout line but have never seen that happen before? I’m considering several potential solutions: (1) regrout with high quality epoxy grout and call it good (!?), (2) fill the open grout line with silicone in hopes of a better more flexible seal over time, or (3) start tearing up tile to see see if pan is in good working order and go from there. Option three seems like best long term solution but am I getting in over my head? Thanks in advance for any help or suggestions.
once a pan is compromised, its best to replace it. by now it is almost certainly 100% saturated and clearly isnt doing its job. the longer it goes the more damage to the structure it will cause, not to mention mold. the tile in the picture is all square set meaning you may be able to take the tile out about 2 ft above the pan to do a replacement. assuming you can get new tile that matchs the old.
A) The gutter on the shower door should not be sloped back to that corner, it should be sloped to the opposite side
B) The curb was not constructed properly because it should have been sloped back toward the shower pan such that any water landing on the top of the curb would roll back in rather than out toward the bathroom floor.
C) The shower pan waterproofing membrane (whatever the method) is supposed to continue up and over the curb and up the wall above the curb, it seems that your enclosure was not waterproofed correctly. I say this because the small amount of settling represented by the crack should not have compromised the waterproof membrane.
I would, unfortunately, recommend tile removal. A "second place" temporary alternative would be your "Option 2", waterproof silicone caulk.
The floor outside the shower looks damp which does suggest the shower pan is leaking and in need of a proper repair. But, before I started removing tiles (with the associated risk of breaking them) I'd peel back the carpet, clean up the damp and then cut a hole in the floor in a safe place so that I could look under the pan. That would tell me how bad the damage was under the pan. You may be able to see where it's leaking by shining a torch through the gap in the mortar. (I'd actually start with small hole and a boroscope to minimise what I had to repair if I got lucky and it was dry under there.)
If under the pan looks good I'd clean it all down with mold and mildew remover, let it all dry out, and then reseal the crack with silicone sealant. I wouldn't bother with grout, it tends to crack at joints like that where two planes meet. That your existing tiles look so clean suggests that the original sealant didn't stick very well - use a sealant trowelling tool to create a functional seal with enough overlap. It'll probably last another 5 years.
Before you screw the patch of floor down, you can buy cheap moisture sensors on eBay which will alert you in good time to fix it if / when it happens again.