Shower Pan: No concrete underneath plastic pan by orig bldr

[DochSavage]

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Hi folks!

I'm in a spot, and I'm hoping that the answer is straightforward. I'm not hoping for easy; straightforward will do. In this case, I've got a 17 year old shower tiled with 4-inch tiles. There have Leaking incidents periodically, with no clear root-cause. To be clear, the pan is 4'x4', with a starburst pattern of foot grips on top, each with a ridge underneath to the floorboard to apparently minimize flexing under body weight.. (Hopefully, that's clear, anyways.)

Recently, the water got behind the tiles, forcing me to clean that wall of the shower down to the studs. This was annoying, BUT it let me get my fingers under the pan.

It's empty. It's just a plastic pan with ridges sitting on the floorboards. There's some give in the pan when you step on it; I'm thinking that movement is what causes the occasional leaking...and is why it is difficult to reproduce. One of my fears is that the floorboards under the pan are water-damaged, but I know of no good way to find out...besides completing the horror by removing the pan.

A friend told me that some contractors would retrofit concrete under the pan, essentially by squishing it into the gap until no more will fit; I would worry about air gaps. Plus, for all I know, this plastic pan is SUPPOSED to be empty; no one has mentioned that as a possibility, but it is possible.

Any ideas on how to stabilize the shower for use? Do I fill up the underneath of the pan with rigid foam or concrete retroactively? Pull the pan and rebuild from scratch? Not worry about the pan, and just rebuild the wall with backerboard, liner, and replace the tile?

Thanks!
Jeff

 

[JRC3]

My guess is the pan should've been set in mortar when it was installed. Since it wasn't it has flexed and moved through the years causing it to develop tiny cracks allowing it to leak. These cracks may not even be visible.

Since you have the shower torn down to the studs, why wouldn't you replace the pan? They are cheap enough and a new pan would look better, not to mention when properly set, feel much better under foot.

Also, was the tile installed over drywall? "Greenboard" or not, drywall has no place in a shower. At least not 5'-6' up from the pan.

If your worried that removing it will be difficult because of the drain, there are easy was around that.

 

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[Cacher_Chick]

It might not be what you hoped for, but often the permanent solution is to tear it out and start over.

 

[Jadnashua]

It's a rare floor (and pan!) that is perfectly flat and level. As a result, most of them will not sit without flexing or rocking on the floor in the desired manner. To overcome that, yes, often, people will use mortar underneath it. It doesn't have to be a continuous spread and in fact, if it is, it's much harder to get the thing supported and level. If it has all of those ridges, it will be nearly impossible to retrofit anything underneath it now. Foam tends to compress (and some types fracture), so may not last. That flex can cause microfractures that can lead to major failures. It also can loosen the seal around the drain, allowing it to leak there - often only when you stand just so to bend things just the right way.

You can rent or buy a drain plug. If you do and install it in the drain...you can then fill the pan up and leave it at least overnight. Other than maybe some evaporation, it should not drop in level and you should not see any wetness outside of the shower.

FWIW, unless you use a topical waterproofing on the walls, the walls are not generally waterproof in a shower. CBU is not waterproof, but is not damaged by being wet. Since it can absorb and wick some moisture, to protect the studs behind it, you typically install a vapor barrier which also keeps moisture out of the walls and insulation. My preference is to use surface applied waterproofing underneath the tile, and of the various types, I prefer a sheet membrane verses a liquid applied one. Done properly, that does make the walls waterproof.