Why water seeping out of the corner of my shower mud pan?

[LilyT]

Small amount of water slowly seeps out of the corner of my shower (red arrow), flow over the small mosaic tiled floor surface towards the center drain hole. My shower mud pan was constructed with a thick layer of plastic liner, where the edge rise ~12" above floor, similar to the picture I found online.

Last night I removed the shower faucet cover, turned off both the hot & cold service stops. I noticed a very tiny wetness around(under) the right service stop (confirmed by the paper at the blue arrow). This wetness is so little that it couldn't be the cause. Besides, all the water pipes behind the wall go thru the middle of studs, if they ever leaked the water would have stayed outside of the raised liner edge and would have damaged the ceiling of the downstairs which is not my case.

I noticed the seeped out water seems like having relatively higher concentration of calcium because it discolored the black grout of my shower floor.

I didn't use this shower in the past 10 days. Could it be condensation?

The curvy tiled shower wall is an exterior wall, exposed to the late afternoon sun. Outside temperature in the past 10 days was between 80~100F, I had AC set on at 80F. I'm puzzled why water appears inside the mud pan liner. Condensation?

 

[Twowaxhack]

Probably water getting into the wall higher up in that corner, then coming out at the bottom. But that’s just a guess.

 

[JG plumbing]

When you say slowly seeps. What do you mean? This has been happening for how long? Constantly? Just one time you've noticed this?

Could be many things.

 

[LilyT]

Bought this house 2 years ago. It came with 4"x4" glass tiles on the shower wall (left side in my pictures), with visible moisture damage behind tiles especially on the bottom row, nearby floor tile grout showed white deposit too. I replaced this side of the wall with larger 12"x36" porcelain wavy tiles, and refinished/restored the black floor grout. The old backer board was USG cement type, the new backboard is foam kind (Hydro Ban Board).
After a year of use, the floor grout near the bottom seamline started to show minor white discoloration again. Sometime between then and now, I applied silicon caulking to the bottom seamline. Then ~2 weeks ago, a noticeable white trace like a dried water streak appeared in the corner pointing to the center drain hole, we stopped using this shower and a few days later applied silicon caulking to the vertical seam of this wavy wall as well. After that, I saw at least twice a small puddle of water at the drain hole which were coming from this corner. This shower wasn't in use in the past two weeks.
The more I wrote, the more it sounds like condensation. I'm just surprised by the amount. I'll keep monitoring the leaking amount in relation to the hot weather & AC usage.
In the meantime, I wonder if it's better to remove the silicon caulking. The tile grout can help trapped moisture to escape. After I replaced 4x4 with 12x36 tile, I have already greatly reduced the grout area. I probably should leave the grout exposed in the air.

 

[GReynolds929]

Sounds like you had an area that showed signs of leaking and you just tiled over without investigating or fixing the leak...

 

[LilyT]

Sounds like you had an area that showed signs of leaking and you just tiled over without investigating or fixing the leak...

So you agree condensation shouldn’t be that much amount, right?
I removed the silicon caulking at the bottom seam tonight, and trapped water came out along that seam line, see picture. Why this water emerge inside the mud pan liner?
To locate the source of the leak, should I remove the wavy tiled wall or the floor mosaic and mud pan?

 

[sawguy]

Did it do this before you installed the 12 x 36 wavy tile?

 

[JG plumbing]

Your red arrow shows a folded corner in the shower liner it looks like that could be holding water. The other possibility is a tiny leak in the copper pipe that the pan is catching... Or something different. There's really no way of knowing without looking.

 

[JG plumbing]

If your have a water meter you could see if your water was running over a period of time without using anything else. That would narrow it down.

 

[Jeff Handy]

The vertical grout line or caulk line along the wavy beige tile looks poorly done.

It should probably be dug out to clean bare tile, clean up the joint with bathroom cleaner then clean again with rubbing alcohol. then put a fan in the shower for a few days.
Re-caulk the joint and fully fill the gap while caulking.

 

[PerplexedPlumber]

Water from condensate wouldn't have calcium, although if it is running slowly down a wall where residue exists, it may pick up a little.

 

[LilyT]

Did it do this before you installed the 12 x 36 wavy tile?

Before I moved in I spent several months remodeling the house. During that time, the water of the whole house was not shut off, no shower was used, all seams of this shower appeared dry. But the old 4”x4” glass tiles showed past moisture damage behind and nearby floor grout had white discoloration. When I opened this wall (I didn’t touch the floor and other walls), I saw USG cement backer board was used, the raised portion of mud pan liner was in good condition, there was black tar paper stapled to the studs to hold loose insulation material inside the wall cavity. The tar paper had no sign of past moisture damage. I didn’t remove the tar paper and insulation behind to see if there was pipes going thru this wall. My contractor put up foam backer board, finished with wavy tiles, and refreshed the discolored floor grout with black paint.
After I moved in, this shower was being used ~10 minutes every morning and ~20 minutes every third night. Several months ago (1.5 year of usage), I noticed floor grout discoloration came back, so I silicon-caulked the bottom horizontal seam. Two weeks ago, I noticed trace of dried water streak in the corner and stopped using this shower. I waited a couple days and silicon-caulked the vertical seam. The next a few days, I found small water run on the shower floor. Yesterday I removed the silicon caulking on the bottom horizontal seam, small water run out from the middle of that seam, this spot is also where the old 4x4 glass tiles had the worst moisture damage. In the following days I will keep monitoring the amount of water leaked from this spot.
Thanks to everyone for helping me tracking down the problem! Appreciate your inputs very much!

 

[sawguy]

Somehow water is getting behind the tile either through the grout, a seam or your shower valve. I think I would concentrate on the valve. You said there was slight wetness at the cold stop.