Without seeing it for myself I can't say for certain what can or can not be done but I suspect your plumber is blowing smoke to cover their ineptness and inflate their bill.

I would remove knobs.handles and trim to see if it's simply a packing leak that can be remedied by tightening packing nut (15 minute job start to finish).

I would follow klem 1's advice. Once you remove the plate that covers the mixing valve, you may be able to detect if it's leaking (you can use your camera to take some photos through the hole - you may be able to confirm if it's leaking from that point).

A few weeks before we began renovating our primary bath, I told my SO that I smelled something musty in the bathroom - but it was only right after he finished taking a shower (he tends to take ridiculously long showers!) When the shower walls were cut out (easier than taking off tile and then removing), contractor confirmed a slow leak from the mixing valve. Maybe you are having the same problem.

Hi @coastal_vibe,

Looking at your photo, it is indeed a shear wall.

Please send us photo of the place where you looked inside the wall. I don't need to see it leaking, I just need to understand where you viewed the leak.

@coastal_vibe

Also, since you can see inside the wall, there's a definitive test for "plumbing leak vs wall leak":

Assuming it's leaking when using the top shower head, you remove the shower head and temporarily install a cap or shutoff valve. Turn the shower on with the end of the shower arm closed off and then look to see if it's leaking inside the wall.

Note that this end of the shower arm is likely to be square- not tapered - threads. If you use a shutoff like the one in the link above, it's made with the proper threads.

Jake the Wonderdog to n the rescue!!!

Jake, I am attaching a photo (below) of the place where leaking was seen when the "leak detection" company was here. I tried reproducing the leak, but I think it needs several minutes of running the water for the leak to become evident. I recall that the leak detection guy fiddled with the trim on the shower valves, but I do not think he removed any trim to inspect the openings.

The curb top and vertical edging of the shower are 2 cm quartzite (natural stone). The baseboard and face of the curb (closely matches color of the stone) are porcelain tile.

Below the recent photo, I am attaching a photo of the shower walls before tiled. I think this waterproofing method for the walls is called "old-school mud float prep."

I have scheduled a tile-setter to look at this next week. A GC is stopping by to look at it also next week. The GC responsible for the bathroom remodel recently passed away.

According to original post this is an interior shear wall. I'm confused as hell by the request for pictures to determine whether it's a plumbing leak or wall leak. I've seen a fair number of plumbing leaks but to my knowledge never witnessed an interior wall leak. Exactly what does a wall leak look like in a picture?

"Will a big chunk of the shear wall need to be cut to access the plumbing?"

Maybe, but so what?

I'd locate the centers of each of the studs adjacent the valve and rip the wall covering there. Now you have access without compromising the waterproofing.

I live in an earthquake region -- criss-crossed by more than two active fault lines. To cut holes in the interior shear wall, I would likely need a structural engineer to assess the increased vulnerability to damage caused by lateral shaking from earthquakes, and possibly need a permit from the City.

Hi @coastal_vibe,

Thanks for the photos. Did you try capping the end of the shower arm? That's a definitive test.

@klem1, the reason to ask for the photos is because I wanted to understand how the shower walls were constructed / waterproofed. When someone is mentioning "drywall" and "shower" in same post, I get worried. To be clear, the leak can be a plumbing leak, or it can be bad construction / leaking waterproofing. It appears that these walls were floated over probably concrete board - so that's good. I don't know the details on the water proofing right now, but at least the walls appear well made.

That said, that water damaged drywall is a pretty classic pattern for water seeping out of the shower along the curb and then down the wall. The curb must tilt slightly into the shower area so water drains in.

Just FYI: The standard leak test for shower plumbing rough-in is to cap off the shower outlets and then pressurize the plumbing. Most mixing valves bases have a test plug to allow this to be done. Assuming this was done, there is a low probability that the roughed-in plumbing is leaking unless a nail/screw hit a pipe.

Again, the sure test is to cap off the shower arm and then turn on the shower and see if it leaks. If it does, it's a plumbing problem. If it doesn't, it's a water proofing problem.

You are overthinking the braced (shear) wall. It is just structural sheathing (plywood) fastened according to prescriptive tables. If you remove any, simply replace it.

No diagnosis yet ...

A GC looked at the problem yesterday and plans to return with a plumber. I am waiting for that, instead of getting on my ladder to try to cap off the showerhead. The GC said, if needed, they can cut a large square of the shear wall and later replace it after repairing the plumbing. Taking out tile to repair from the front would be the most expensive and last-choice option.

I had a tile setter here today -- he thinks the waterproofing was done correctly and that it is most likely a plumbing problem. The plumber who did the installation made several mistakes throughout my home -- I later found out that he had a suspended license at the time and was working "under" the (now-deceased) GC's license.

Update -- no resolution yet ... still waiting for another plumber to look at it.

I called the "Leak Detector" guy to remind me which tests he had run. He insists that the problem is the waterproofing on the walls and not a plumbing problem.

1) He said he did not run the test of capping off the fixed showerhead because he knows it is a waterproofing problem (while admitting that he knows little about waterproofing).

2) He said that water is spraying from the fixed showerhead and splashing onto the tiled wall at the shower entrance (even if no one is in the shower). Should waterproofing on walls extend beyond the shower compartment? If so, how far?

3) He claimed that his co-worker had cut the shear wall behind the shower plumbing when I first called them about the leak 1-1/2 years ago. No, only the drywall was cut.

At that time, the "Leak Detection" guy blamed the leak on a gap between the pivot door and the plumbing wall. I had the glazier tighten the gap with a seal on the door. I was led to believe that the problem was fixed. A few months later, I had the drywall repaired and had the bathroom repainted.

And then, the leak re-appeared in the same corner. Did I mention that the Leak Detection company charges $350 per hour?

" Should waterproofing on walls extend beyond the shower compartment? If so, how far? "

Is the shower open, no door or glass panels? If so, yes of course the waterproofing needs to extend probably 3 feet outside the shower.

Oh my goodness!

Just cap the end of the shower arm already and stop messing around with everything other than a definitive test.

This is something that should have been resolved in about 20 minutes -as to the source of the leak anyway.

It does not require multiple visits over multiple weeks by various "experts".

Update -- my regular plumber stopped by today. He ran the pressure test with capping off the shower head -- no plumbing problem seen.

The Leak Detection company called back while the regular plumber was here and explained that his employee had run a pressure test (but not the same one as done today).

Resolution? Only advice that I have been given is to use the shower and keep a rolled up towel near the entrance where the pivot door is hinged to the wall.

This bunch of plumbers,leak detectors and contractors surely no how to milk a good thing when they find one.