My upstairs shower has tiled floor and walls. Water leaked to the downstair ceiling. It didn't happen all the time. It happened twice so far. Both time happened when the shower was being used for more than 20-30 minutes. A plumber came and couldn't find anythng wrong. A contractor came and suspected that the shower pan had a crack. To fix it, the whole shower floor needs to be torn apart and rebuilt the shower pan.

I did the following test to test the shower pan yesterday afternoon. Duck-taped the shower drain and filled the shower floor with water - about two inches. I marked the water level. During the next 15 hours, I noticed that the water went below the marker. I refilled the water to the original leve from time to time. No leaks has been observed. What else can I do to pin-point the leaking source? Is it necessary to re-construct the shower pan? I would like to avoid it if possible. I noticed missing grout on the shower walls and saw tiny gaps between tiles due to the missing grout. How can I find out if it is the walls that caused the leak? If the water enters through the walls, will the water be collected by the shower pan underneath the shower tiles? Your help is much appreciated!

I had a similar problem, drove me nuts trying to find it! And it was not in the walls or shower pan, but in the drain pipe connection -- and it would only leak if you were in the shower. Anyway, this is how we found it:

1. did what you did to eliminate the pan.
2. covered the walls with heavy plastic and showered regularly to see if the leak continued to determine if the leak was through the wall tiles, grout, etc.
3. put newspaper outside the shower floor to make sure it was not somehow leaking/running out onto the floor and leaking through there.

Ultimately it was none of those. With the weight of the human in the shower, the pvc drain connection would gap just enough to make it leak.

Good luck!

Stop by hardware store and get a 1/2' threaded PVC pipe cap. Remove shower head. Screw pipe cap onto end of shower arm. Cap needs to be installed reasonably tight but it does not matter if it leaks a little. Turn on shower. Wait for 30 minutes. Check for leaks.

If leak occurs you have a leak in water supply pipes. Probably where shower arm screws into pipe inside the wall. Pull escutcheon around shower arm away from wall and with flash light look in side wall for signs of water. If you have an access panel on the other side of the wall that has the shower valve, remove the access panel and look for signs of water. If you do not have a access panel, remove shower valve handles, valve stem covers and escutcheons. Look look inside wall for signs of water.

If there is no leak while you have the pipe cap installed get a flat rubber drain stopper and put over shower drain. Using a bucket and water from another source, fill the shower base with about 2" of water. Check for leaks. If no leaks get in shower and walk around. Check for leaks. If you have a leak you have a cracked or leaking shower pan. If no leak occurs while you have the shower pan filled with water, remove the drain stopper. If leak occurs while water is draining you have a leak in drain piping. Most likely at the connection to the shower floor.

If none of these things make the leak occur you will have to start looking for leaks through tile walls.

For some time PVC in sheet form has been used to build shower pans. Prior to that sheet copper was used. Neither will crack. A leak could develop at the drain connection. You could have a leaking shower pan but it is seldom the problem

Sewslikethewind, thanks so much for your quick reply. I did #1. For #3, I checked but didn't notice any water on the floor outside the shower. I need to try #2. Besides eliminating the three possible factors you listed, is there any way that I can test the pvc drain connection directly? Thanks!

I did have an access panel but missed it anyway because I didn't look when someone was IN the shower -- the added weight of a human was the only time the shower leaked.

I understand your frustration. I had two different plumbers look at it and was ready to demo the bathroom, it was ruining my kitchen. You might try the other responders suggestion, they might be more experienced in this matter, this is just what worked for me in my situation. Something will work, keep trying!

Hi Sufud and kudos for doing what your lazy contractor failed to do. You say the water level dropped in the shower floor but you didn't notice moisture on the ceiling? Did you figure the water seeped past the duct tape back into the drain?
Bob wants you to check the valve and water connections while I think you may have nailed it with the tile grout. Let me explain.
You're in the shower and the shower spray's hitting the wall with faulty or grout that has shrunk over the years. The shower spray runs past the grout and runs down to the floor OUTSIDE and IN BACK of the shower pan past the floor and through your ceiling, That's my thoughtsd.

Sewslikethewind

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With the weight of the human in the shower, the pvc drain connection would gap just enough to make it leak.

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That's what happens when a plastic shower floor bedded in at the time of installation. You have a ruptured drain seal. Purchase some plumbers putty or Silicon Jel, unscrew the top of the drain, form a rope of putty or jel and replace the seal. Be advised that this will happen again if the shower floor is not bedded in so it doesn't flex and give when you step into it. Good luck, n bTom

I tested the shower header yesterday using a pipe cap and didn't see any leak.

I also used a hose and sprayed the shower walls for 20 minutes and still didn't see any leak.

One of my upstairs neighbors told me that she had to have her shower replaced a few months ago. Her contractor told her that the floor of the shower was not lined or constructed properly. I don't know exactly what it means. Is there any way to test what her contract said?

Will the thermal Imaging help detect the leak in my case? I feel that I am running out of ways to find the leak.

Thanks!