Sunken Shower - depth, curb, or ramp

Discussion in 'Shower & bathtub Forum & Blog' started by Jelly, Jul 16, 2009.

  1. Jelly

    Jelly New Member

    Messages:
    15
    Building a new house - my foundation guy is putting out form boards today and I am trying to get everything right.

    The custom built master shower will be "sunken" or in other words like a depressed spot in the slab. I would like to do either a shallow step down or even like a beach entry into the shower.

    The question is how deep should we make the rough depression in the slab. We have plenty of room to work with (slab is elevated, floor level is 18 inches above grade - I'm in south Louisiana).

    I need to make sure I make it deep enough to maintain at least 2 inch difference between bathroom floor height (the part which is not sloped to the drain) and the finished drain height. But I don't want to make it so deep that the step up would be more than 7 inches.

    How much mud can I expect to have between the bare concrete and the top of the finished shower tile floor? How much mud is too much?

    Given the width of the shower and maintaining 1/4 inch per foot of slope to the drain, I am thinking I should make the rough dimensions of the depression in the concrete slab anywhere between 8 and 12 inches deep. I guess it's better to go too deep than too shallow, because I can always make up the difference with mud. Am I wrong in assuming that?

    I hope I've given you enough info - please let me know if I need to clear anything up. I guess if you could only address one question, it would be how thick of a mud bed can I use to make up differences in height. For example if I've got, say 8 inches of mud at the edge of the shower, sloping to 6 inches of mud by the drain, is that too thick?
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,055
    Location:
    New England
    You need to account for two layers of mud, one for the preslope, then the liner, and then the setting bed. The bottom one can taper to nearly nothing at the drain over the concrete. You probably want the top layer to be at least 1" thick all across since it can't bond to the concrete and would be floating on the liner.

    I think a step down would end up being dangerous, as it could be wet.

    You could get by with a single, sloped mudbed if you used a sheet membrane like Kerdi from www.schluter.com.


    Check out www.johnbridge.com for help in building the shower.

    You will want a liner, and it is easier to make the depression flat, then build the slope with your mudbed.
  3. Jelly

    Jelly New Member

    Messages:
    15
    jadnashua, thank you for responding. At first I didn't understand what would be more dangerous about a step down than a typical shower curb if they were of equivalent heights. Actually the step down initially seemed safer, because it always feels awkward to step over that curb, or worse yet stepping over the deep edge of a tub in a shower tub combo. But then I realized the difference is you normally don't step *on* the curb, rather, you step over it onto a dry floor. So maybe you're right.

    Ok, so if my goal is a sloped roll-in or beach entrance, then how much overall thickness do you think I need to account for? Including both layers of mud, liner, tile, et cetera, from the bare concrete to the top of the tile floor? A friend of mine said I could really use as much mud as I need, but of course I don't want to put a ton of it in there because of cost of material and the effort to make it work. I just want to be sure I give myself enough room for all the layers.

    You said, "You will want a liner, and it is easier to make the depression flat, then build the slope with your mudbed."

    Just trying to understand - I know the concrete of the slab needs to be flat. Is that what you mean?
    Last edited: Jul 16, 2009
  4. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,055
    Location:
    New England
    Yes, slope the mud, not the concrete. The total depth will depend on the size of the shower. As noted, over concrete, you can taper the mud to near zero under the drain, then 1/4" per foot to the edges. Over that, the liner and then a setting bed (parallel with the sloped bed). You want that layer at least 1" thick all over. Then, add the thickness of the tile and allow a little for the thinset layer.

    You really should check out www.johnbridge.com on constructing the shower. If you have a plumbing question, these guys are good. I personally, really like a non-traditional shower using a surface membrane like Kerdi. Especially in a potentially humid area like Louisiana. By using a surface membrane, you have waterproofed the mudbed and walls, so there's very little that can get wet. Much less chance of mold. You could carry the waterproofing out into the main bathroom if you used Ditra as well. A really nice system.
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