I installed a shower valve I installed a custom mortar shower pan (pvc liner with plastic vapor barrier behind the walls) I installed cement boards on the wall

the area on the front of the cement board around the shower valve, a diagonal line (as if water was dripping down) going to floor and a larger area of the mortar pan in front of the drain are mysteriously wet. When I removed the cement board the back of the cement board was dry (however in between the pvc liner and the plastic was wet also some of the studs were moist) all the copper pipe, joints, and shower valve appear to be dry.

What is causing the moisture? can it be evaporation from the drain? condensation?

What can I do to fix this?

  • Joe, I suspect you have a leak in the hot or cold water pipes/fittings, or from the shower valve itself. Sometimes very small "pinhole" type leaks are very difficult to detect. To prove it out, I would recommend (if possible) shutting off the water supply to that area and waiting to see if the problem persists or if it dries out. Also check to ensure the water is not coming from somewhere above, like other plumbing, A/C condensate line, leaky roof, etc. Sep 8, 2017 at 19:39
  • Agree with @JimmyFix-it & that possibly, with the cement board removed, the pressure you are otherwise placing on the piping joins is not there, so no leak when you have it off. Other possibility, what slope is the water piping that penetrates the board at? Was it sealed/caulked or gasket to prevent water in use from getting past it?
    – noybman
    Sep 8, 2017 at 21:18

1 Answer 1


It seems like randomly(every 2 to 6 weeks) the faucet leeks(it turns on a little) and water was coming out the top of the pipe where the shower head was to be connected. If you open and close the handle it turns off. as a temporary solution I installed the shower arm so the water drips in the shower instead of behind the wall. I plan on contacting delta faucets. If I installed the valve properly it must be faulty.

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