Help with Membrane Shower Pan Repair

[Rossn]

In the process of installing some radiant heating, I had to tunnel through a double LVL supporting block for the radiant lines, and didn't have good light and had a bit of an oops, cutting the shower pan. Drat. I've since removed supporting block and a small area of plywood under the shower.

How do I know what material it is made of, and how it can be patched? I'm hopeful it is PVC, because that sounds repairable, but don't know much about shower pans.

Many thanks for your guidance.

 

[Jadnashua]

Well, it seems you may have more than one problem. IF that's a pvc liner, and it appears to be flat on the floor, it was never installed properly in the first place! Neither tile nor grout is considered the waterproofing layer in a shower...they are a decorative, wear surface. The liner in a conventional shower pan is required by code to be sloped to the drain, so it should never be flat on the floor. There should be nearly an inch or more of mortar on top of the subflooring before the liner is installed. Industry guidelines call for it to be a minimum of 1.5" thick, but people often go thinner near the drain to minimize the buildup height. But, over a wooden subfloor, it still needs to be at least 3/4" and 1" is more reliable as a minimum.
To patch a pvc liner, you'd need the pvc cement and some pvc material itself so you could make a patch similar to say a tire.

 

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[Rossn]

Thanks! Yeah, I agree, and was expecting there to be something else hard over the subfloor (mortar or something else). You can see in the picture how close the drain is, so it is possible they sloped the edges and not here, though that would be odd, given how flimsy and rotted the 1/2" subfloor is. The contractor who did this work for the prior owner had many omissions and errors, so it is also possible they didn't know what they were doing.

It is also possible this is an additional underlayment below the first layer of grout, and may not be related to actual drainage. The build up inside the shower (relative to floor outside) is seemingly substantial, though it is sloped pretty significantly at the edges.

• Can anyone tell me if it is possible to have a liner that close to the subfloor actually drain into the drain, or if some build up/elevation is typically required? (trying to determine if this is a secondary liner... possible to tell by another means?)
  
• what are the possible membranes (I see PVC and CPE and am sure they use different glues), and is there a way to tell a difference? Maybe someone will be able to tell via the photo.

 

[Rossn]

Here is the drain that was used, and they basically recessed the flange to be level with the subfloor. Through close inspection, the membrane shown does go into the flange. The membrane is flexible, but feels more like plastic than rubber, if that means anything. If I pull down the lip of the cut, it snaps back up with a bit of popping sound.

I guess it is possible they also have a membrane within the mortar bed, but it would be a bit odd to have those two come together as a sandwich at the drain flange.

 

[Jadnashua]

That drain is a typical clamping drain used with a liner. The Tile Council of North America (TCNA) handbook is the industry bible. They call for the minimum thickness of a mud bed over a wooden subfloor to be 1.5" (although many go thinner at the drain, but usually still 1" or so). There is no way the liner should be flat on the floor to meet industry guidelines or the plumbing code.

The plumbing code requires that the waterproofing be sloped to the drain. Neither tile nor grout is considered the waterproofing. The tiled surface is sloped because the material underneath it is, but to get that to happen, there's three layers:
- a preslope
- the liner
- an equal depth setting bed (i.e., parallel to the preslope and liner)

To save time and effort, it's not uncommon for people to omit the preslope. Especially if a plumber is called to install the drain. Otherwise, you need the tile guy to make the preslope, then call the plumber, get the flood test for the inspector, then the tile guy back to finish things up. What tends to happen if you've got a good tile guy, is the plumber installed the drain and the liner, tests it, then the tile guy tears the liner out, does a preslope, and puts it back in.

There are numerous ways to make a shower outlined in the TCNA handbook. None are particularly hard, but they are very detail oriented. If you follow one of them, you'll have a reliable, long-lasting shower.

Water WILL get beneath the tile in a shower pan. It will percolate down to the waterproof layer, and if it is properly sloped, it will slowly drain out, but nominally, be constantly damp. It's a first in, first out scenario. If the liner is flat on the floor, water will tend to accumulate and stagnate. This can keep the grout wet, and promote mold. Properly mixed deck mud is quite porous, so water will move through it. It's not particularly strong for abrasion, but is in compression (the tile cap it, so there's not an issue).

 

[Rossn]

Thanks for the information, as I have a couple (different) poured pans in my remodel that will need to be done.

Interesting thing is that currently, it is bone dry inside. Maybe there is some upper layer as well... not sure.

Anyhow, I went to three supply houses, and no one recognized the material (definitely not PVC). So, I decided to call TiteBond, as I really like their products, and you can talk to an actual chemist/scientist with technical questions. Without knowing the material, it was hard to say, but he did say epoxy would not bond nearly as well as their Weathermaster Ultimate MP, which I've used a ton of on my project, and recommended squirting it inside the joint, as well as on the outside to create a connected sandwich. So, that's what I did. That product is a really great product - bonds to almost anything, low VOC, long life, UV stable.