Sewer gas from shower drain and water pooling on tiles. Help!

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New Member
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Palm Springs, CA
We purchased a 1971-built home in Palm Springs about 2 years ago. It was a fresh renovation, which included replacing the tub in the master bath with a tiled shower. About 8 months ago, we noticed two things happening: there is a persistent sewer gas smell from the shower drain that gets worse when the shower is running; and water started puddling on the floor tile near the drain as though the floor pitch had somehow changed and some water was unable to drain away. It's almost as though the drain assembly has somehow been pushed up from below (though not enough to damage the floor tile). There is consistently water in the trap, visible about 8 inches below the shower floor. There is no smell from the kitchen or second bath. The home is built on a slab so there's no access to the plumbing. We had the main line scoped and it's clear. Snaked the shower drain. Used drain bladders to hose out the shower drain and the vent pipe, and found no blockages. Poured chemicals down all the bathroom drains and the vent pipe. I'm planning to jackhammer out the old floor tile and install a new Kerdi-board pan and tile to solve the slope issue. I'm hoping I'll find some clue to the sewer gas smell when everything's opened up. Maybe the shower trap is too shallow? Could the shower drain somehow be siphoning waste from the main? The plumbing layout for the master looks like this:

street <<<<<< shower < commode < double sinks < main line cleanout

John Gayewski

In the Trades
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When the line were scoped did they look for sags or reverse pitch in a nearby line. You could be getting soiled water running from a toilet that is traveling the wrong way. That's what this sounds like to me.
Another possibility is a trap riser (tailpiece) that is too long and causing the water level in the trap to be too low due to siphon.


Retired Defense Industry Engineer xxx
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New England
A common problem with showers is improper construction. One study I was shown during a class said that 70-80% of the tiled showers in the USA were not built to industry standards.

Neither tile nor grout are the shower waterproofing, but the majority of moisture is stopped from penetrating because of the slope and just runs to the drain. Some inevitably does penetrate the tile into the substrate. Assuming there's a waterproof layer, the plumbing code requires it to be sloped to the drain at a minimum of 1/4" per foot. In a conventionally built shower, there is a clamping drain that will have weep holes in it. Those often are not kept clear, so water can accumulate, or the liner is not properly sloped, so it acts like a big bowl, holding water. That can fester and smell really nasty after awhile. Another very common mistake is if the liner is installed flat on the floor. That doesn't meet plumbing codes, and won't leak, but it WILL accumulate stagnant water.

It's normal and proper to have water in the trap. It's not normal for it to back up into the shower. Chemicals usually don't help. A good camera scope operator should be able to identify any problems with slope or obstructions, but not all of them are good! Are you on a public sewer or a septic system?

I like the Kerdi system, but lots of various methods all work IF done properly. Note, the foam tray works quite well, but it requires the floor to be flat and level. If that isn't true, getting it there prior to setting the tray may be more work than building the pan out of deck mud (really cheap stuff) that has the advantage that it can be made any size and overcome any irregularities in the floor. Deck mud is more like playing with wet beach sand than doing concrete work. The difference is there's a limit on how much time you have to work it versus playing at the beach!

Check out for help with building your shower.
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