Subfloor prep for new shower pan


Old 06-19-05, 06:57 PM
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Join Date: Jan 2005
Location: USA
Posts: 53
Red face Subfloor prep for new shower pan

Hello all!

After finding that our shower had apparently been leaking for years and had basically liquified the subfloor underneath it, I pulled out not just the shower but the whole bathroom: tiles, walls, ceiling, and a large portion of the subfloor down to joists. I have since replaced the plywood subfloor and then added another 3/8" plywood layer, screwed down every four inches. Since I am going to tile the bathroom, I was next going to put down thinset and 1/4" Hardibacker with screws. Here are my questions:

First of all, should I put the cbu down over the entire floor and then build the new shower pan on top, or should I put the cbu down everywhere except where the footprint for the new shower will be? Or if cbu isn't appropriate, should I put down another layer of 5/8" plywood under the shower pan?

#2 Is it acceptable to use 3mm rubber pond liner as a shower pan membrane? I built a pond in my garden a few years ago and have a very large piece of the stuff and it's 12 ft wide.

#3: What is the current thinking about building the shower dam out of concrete bricks instead of wood 2x4s? After seeing the mush that the old shower dam had become, I'm a little jumpy about wood. If I were to use concrete bricks, should I put thinset between them and the floor or what?

And finally #4: After building the pre-slope in the shower floor, would it hurt to paint the surface of the pre-slope with an elastemerized rubber roof coating to further waterproof the pan? The membrane would go on top of that.

Thanks for your help. I want this shower to NEVER, EVER leak again!

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Old 06-20-05, 04:56 AM
Join Date: Oct 2004
Location: New Jersey
Posts: 1,132
Hi Tina. Keep this as your project thread so we can keep up on the whole project along the way, pan, floor, etc. For your first questions,
1)Just use hardi over the floor area, not the shower area. On the subfloor of the shower, use tarpaper and diamond lath, then your mud. If your 3/8 layer was screwed into the joists, back out those scres and relocate them away from the joist.
2) no, it's too thick. At 3mm thick, your corner folds will be greater than 1 cm thick. Won't be able to tuck and alow for that as you do your walls. You'll also end up with a heck of a time getting your dam corners nice and flat.
3) As long as you use preformed shower dam corners and do not pucture the membrane on the top or the inside of the dam, you could pull the shower liner 15-20 years from now and the wood will still look new. While you could use block or brick, it would not be as easy on a wood floor and will be more dificult to fasten the liner on the outside. Don't use PT lumber either. Your shower failure was from imprper installation, as long as you do everything correctly, you willnot have a problem.
4)No need for a waterproofing layerunder the liner. No water should ever get under there in the first place.

If you want to do some really fancy stuff, or are concerned about the integrity of a shower pan built with a cpe or pvc liner, look into Schluter Kerdi membrane. You apply the membrane over the entire enclosure, walls, floor, and then tile directly on top of it. No liner, and your preslope is your only mud bed. They also make preformed pans if one would fit the size you want as well as preformed curbs to fit over 3 stacked 2x4's.

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