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Curbless shower on below grade slab

Posted by californiagirl (My Page) on
Thu, May 31, 12 at 16:01

I've looked at a lot of threads in several of the forums but nobody seemed to have exactly our situation, so I'm hoping to get some advice/feedback on our plans. Has anybody here installed a curbless shower on slab?

We are intalling a new, all tiled bath in our below grade basement (@55 degrees at floor all year). The room is interior to the basement, with no walls on the perimeter of the foundation.

We are planning for an infrequently used curbless (European style) shower, where the water just drains to the center of the bathroom floor. The main house drain runs right below this room anyway and the curbless arrangment offers flexibility missing in our smaller shower enclosures upstairs. The main purpose of this bath is to offer a toilet on a floor with entertaining space and a wet bar.

Inspector says as long as there is 30" of clearance all around for the shower the flooring situation is up to us, but of course we want some sloping toward the drain so water does not sit on the floor and mold.

Inspector suggested that our experienced tile guy can probably create the proper slope, while our concrete shower pan installer seemed to think we would need him to create some curbing against the wall to keep water away from the walls and to the create the proper slope. The shower head will be installed in the the corner of an 8' by 8' room. Do we need outside corner curbing to protect the tiled walls?

I also read on here that we may want to create a thermal break between the tile and the slab and even to install low voltage under floor heating on top of the thermal break material (cork, proprietary brands like Kerdi, etc.). This certainly sounds like it will make the shower more confortable to use, but there are no bedrooms in the basement and this will be the 4th full bath in the house, so we don't expect the shower to see a lot of use. Is thermal breaking and underfloor heating overkill? Could just running hot water work?

Headroom is an issue in this room so we do not want to raise the floor much as part of creating the slope and any other improvements.


Follow-Up Postings:

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RE: Curbless shower on below grade slab

First, there's no need of any curb next to the walls. A minimum pitch of the tile floor of 1/4" per foot from the furthest point to the drain will be sufficient to bring all the water to the drain. What you might think about is using a sirface applied membrane that can go from the drain, using either a Schluter Kerdi or Laticrete Hydroban drain, and then bringing the membrane up the walls, so the whole thing is continuous, and the only thing that gets wet is the tiule and grout. As for the heating mats under the floor, Keep in mind that this is slab on grade, under a building. That floor won't get much colder than the air temp, and running the warm water on it will take care of that in no time.


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RE: Curbless shower on below grade slab

With a surface applied membrane, you do have a thermal break, in a good enough kind of way.

The slope is the most important thing. Membraned of course.

Heat: a subjective thing, in many ways. But, any heat you add to the tiled bathroom will be a plus, a good thing, not a bad thing.

Without any heat in the bathroom, some people will want to spray hot water around the walls to warm up the tiles, some won't. It's subjective, it's personal, and I cannot say whether or not the shower area will feel cool or cold or too cold, and to whom. I wouldn't worry at all, since it's not on a cold exterior wall.

If you do heat it in any way at all, that heat will spread out and end up adding warmth and comfort to the (no doubt cool) basement. So, instead of heating adjacent rooms' air with convection, you can heat the bathroom tiles somehow. Example: a heat lamp, or any incandescent bulb. Example: anything that is warm.

I once had a heated fishtank in the coldest corner of a room. It equalized the heat across the 3-d space. Being permanently on, it spread (a small quantity of) heat permanently into the rest of the space. Tiled areas feel cold because tiles are a heat sink. So, it is nice when they are slightly heated. That's my final answer.


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RE: Curbless shower on below grade slab

First..do a moisture test on your existing slab. You want to see if moisture vapor is coming up into the basement from under the slab. Tape a 2' square sheet of poly on the floor and see if there is any moisture under it after 48 hours.

If the moisture is significant, it might play into what type of membrane you use on the floor. Memebranes like Hydroban and Kerdi have similar properties when it comes to liquid moisture, yet differing properties when it comes to moisture vapor transmission.

Significant moisture drive could actually lift and delaminate a topical membrane from the slab.

If you have under-slab drainage or radon ventilation pipes, and foundation perimeter footing drains, you should be in fine shape.

I'd make it a wet room, pretty much follow Bill's advice;

-slope the entire floor to the drain.

-topical membrane on the entire floor and up about 6" on all the walls, or just fully membrane all the walls. Fully membrane the shower walls.

-ventilation. Don't skimp. This room will be cool and the basement itself is typically humid, so latent drying action will be less than in an upstairs bathroom. Do what you can to eliminate moisture vapor as it is generated.

-I'd not insulate or heat the floor.

You might have to balance relative humidity in the basement as a whole with a heat source in the bathroom. If you do have vapor drive into your basement, it might help to have something as simple as an IR bulb on a timer to help with the initial drying of the room.

For a humid, slow-to-dry shower environment;

A non-porous porcelain tile might be better than a porous natural stone tile.

An epoxy type of grout might be better than a portland-based grout.


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RE: Curbless shower on below grade slab

Great advice from the pros! Thanks so much. Will check for moisture coming up but I remember doing that when we first moved in and didn't get anything.

I will see what the electrician says about adding a heat lamp overhead (cheaper than coils but there is a bunch of HVAC in the ceiling). The room does have forced air and is on a whole house fan system. Maybe we should put a fancy humidity-triggered switch in there to make sure it really dries out after showers?

I have asthma, so we run the furnace fan all the time and have dehumidifiers and UV lights attached to both furnaces.

Any votes on preferred membrane? Is cork not an option because of running it up 6" or more on the sides?


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RE: Curbless shower on below grade slab

cork is great but not a shower membrane.


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RE: Curbless shower on below grade slab

Hydroban. That way, even if you DO have moisture coming up through the slab, it won't lift, being that Hydroban is not a vapor barrier, while Kerdi is.


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RE: Curbless shower on below grade slab

I wa t to remove the tub and I stall a curbless snower in the 6x8 bathroom. The house is built on a slan. Can this be done? Is there enough room to slant the floor toward the existing drain in what was the bathtub?


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RE: Curbless shower on below grade slab

Reviving my old thread to ask the pros for further advice. Serious illness sidelined the designer/GC so she is only now finishing that bath.

What is recommended for board on the walls and ceiling? Every trade has a different idea. We have leftover board from the plasterer and a little leftover cement board. I was sure the whole wet room should be cement board, but the last guy (stone fabricator, we are using remnant from kitchen) said that cement board will wick moisture up from below (even with membrane?) and recommends a board sold by The Tile Shop for this purpose. Help!

Our two upstairs showers had mud jobs with curb all around, then cement board above. Seemed to be the local standard practice.


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RE: Curbless shower on below grade slab

Our tile installer used greenboard in the bathroom around the sinks/tub and cement board in the shower. He used Hydroban or a similar product to coat all of the cement board and the entire floor (slab) before any other material (tile) was installed. What is the exact board your guy is recommending?


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