Diagnosing Tub Leak

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  • Older home (1897), ceramic-coated cast iron tub on second floor (set into a tiled cabinet/surround)leaked during and/or while draining a bath.
  • Leak made its way through the ceiling of the kitchen below, dripping from a recessed light fixture.
  • No leak was detected while filling the tub — someone was in the kitchen at that time.
  • The shower that sprays into the tub had been used recently without any leak detected.
It seems like the leak is either from the tub or the drain, but not the "supply side" plumbing. What would account for the leak only happening during tub use and not the shower? A crack in the tub seems rather unlikely, don't you think? Could shower water hug the drain plumbing in a "different way" than bath water because of the difference in head/pressure (i.e. free flowing vs. loaded)?

Any ideas on how to diagnose what/where the problem is? I know water can travel a good deal sideways, but I think it's heading pretty straight down. Perhaps we go through the light fixture and get a look? Alternately, since we don't want to destroy the tile and cabinet/surround the tub is set in, we could potentially go through the wall from the adjoining room, which is a closet -- less aesthetic/financial impact?

Thoughts? Thanks in advance.


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It seems like the leak is either from the tub or the drain, but not the "supply side" plumbing. What would account for the leak only happening during tub use and not the shower?
Water getting spilled out on the floor during a bath from sloshing around could account for that.

Water leaking from the overflow pipe top area as the water rose to the overflow could account for that.


The Plumbing Wizard
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Bothell, Washington
For locating a leak on a tub/shower, there are several steps. We start low and work ourselves higher as we go.

Does the tub hold water? Pouring water in the tub, and then checking for a leak on the lower drain.
Is it the overflow leaking? Sometimes when kids fill the bathtub higher than the overflow, and the gasket there isn't sealing, that can leak below. I say kids because so often when I get that call, I ask if any kids recently took a bath. Oh yes, yep.
Okay, we're checking the overflow.

Some tub spouts are the cause. When the diverter is pulled up on the tub spout, does water leak into the wall? That's also a common one. A new tub spout is often my cure. I favor the Delta spouts with their weird adapter as that let's me use a pipe nipple or solder onto copper. A good slip spout on copper also works. Moen makes a good one.

Okay, maybe not the tub spout. Is it the caulking around the wall plate and tub spout. You shower with your back to the shower head and the water bounces off your body and onto the wall with the controls. Make sure that has some clear caulking. Yes you can use white too, kind of noticeable though. I can see white caulking from the kitchen it's so obvious.

Is it the shower head? Sometimes those crack over time? I had one condo where the tenant on the third floor was showering with a dangling shower head and arm. Replaced the shower arm and it was all good.

I had one where the shower head was spraying sidewise over the curtain. And they didn't even notice. Weird.

And then the was the one where I asked first if the husband was showering with the sliding doors open. Oh no, he wouldn't do that.
So I cut drywall, opened up ceilings and found nothing. I'm telling you "NOTHING".

A year later I go back, walls patched and painted, I'm there for something else. Did you figure out the shower leak?
Yes, my husband was showering with the slider door open. Dooh!!
Hey, wait a minute.

This is awkward, but...

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