Cast concrete soaking tub

Discussion in 'Shower & Bathtub Forum & Blog' started by splatgirl, Jun 29, 2005.

  1. splatgirl

    splatgirl New Member

    I'm planning on forming and casting a Japanese soaking tub (Ofuro) from concrete. The tub will sit on a sturdily reinforced slab on grade concrete floor. Dimensions will be 42x42 by ~36" high and the walls will be ~4" thick. (The slab has insulation, PEX for radiant heat and vapor barrier under it in case that matters).

    When my plumbers did the under slab rough-in, they boxed out an area under where the tub will eventually sit, leaving what amounts to a hole in the slab where the trap and drain will presumably be brought up.

    #1. Can I have the plumber install the trap and drain at the appropriate location/height and then pour around them, filling the hole and forming the floor of my tub, or is there a reason these can't be embedded in concrete?

    #2. I assume a regular tub drain and stopper mechanism won't work in this situation. A floor drain and flat rubber stopper are fine as far as I'm concerned, but will this meet code? Is there a better solution?

    #3. What about the overflow? Do I have to have one? If so, how to do in concrete?

    #4. I was told that it's a bad idea to put valves and fixtures directly in concrete because it makes repair or replacement difficult to impossible, so I've planned to locate the fixture in a framed wall that backs up to one of the tub walls. Is there any better way?

    Thanks in advance for any advice!
    Last edited by a moderator: May 30, 2012
  2. Terry

    Terry Administrator Staff Member

    Bothell, Washington
    The worst problem with a concrete tub, is heating it. If it were a hot tub, it would be constantly heated and ready to use.

    Since this is a tub, you will have a hard time overcoming the solid mass of concrete that will be needed to be brought up to temperature.
    This is what I used when I wanted a tub like that.
    They make cable waste and overflows that may reach high enough.
    or in my case, I bent some some copper rod and extend a PP W&O.
    You could also use standard glue type W&O fittings.
    Last edited: May 30, 2012
  3. splatgirl

    splatgirl New Member

    The house is heated with hydronic radiant. Since I installed the PEX myself, I was able to place extra loops under the tub location to keep things warmer in that area. Since the tub will be continuous with the floor, I anticipate the temperature of the concrete structure will remain at or near that of the underlying slab (~80-85 degrees) of the many comfortable benefits of the heat-transfer effect of radiant. Hopefully this will offset the heat loss from the water enough to avoid the need for a separate heater.
    Were it not for using radiant, I wouldn't have considered a concrete tub for exactly the reason you mentioned. If it ends up that I still lose all the water heat to the concrete, I'll look into one of those ofuro heaters.

    I have looked at the tub pictured previously and would consider it as a last resort. Honestly, I think it's ugly and not in keeping with the look of rest of the room/house.

    Thanks for the tips on the overflow.
    Any ideas to avoiding having a framed wall just for the fixture? I was thinking about the possiblity of a ceiling mount tub filler like Kohler's Laminar, since then i could locate the valve and handle elsewhere in the room (like deck mounted on an adjoining counter) and avoid the framed wall. Thoughts?
  4. Terry

    Terry Administrator Staff Member

    Bothell, Washington
    You may want to look into John Bridge's tile forum about waterproofing your tub.

    There should be any number of attractive ways of supporting a fixture in your case.
  5. jimbo

    jimbo Plumber

    San Diego
    I also had some questions about whether a concrete tub could be made waterproof, but had no experience; didn't want to even bring it up. I bet the John Bridge folks will have the answer.
  6. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    New England
    Kerdi could do it (keep it waterproof), but the drain is a problem; they have a prototype version for a tub, but the only current production drain is for showers. That assumes you are going to tile it. Kerdi will only work with a special thinset in drain; no clamps. Comes in either an abs or pvc version to connect to the line. Kerdi is a waterproof membrane with an attached fleece thatyou thinset in place. Overlap by at least 2", and you've got a guaranteed waterproof layer you then tile over.
  7. one small queston

    I am wondering about the wood and how it

    keeps from getting moldy over time,

    also how do you keep this clean and tidy looking

    In the links,

    it is basically something a public bath something
    like a common hot tub from what I read.

    What does it take to keep this clean after draining the tub??
    Last edited: Jun 30, 2005
  8. hj

    hj Moderator & Master Plumber Staff Member

    Cave Creek, Arizona

    If your tub is like 95% of the ones like it in Phoenix, it will only be a short time before it becomes a decorative planter. Usually after it is used a couple of times and you realize how uncomfortable it is with the vertical sides, square corners, and flat floor. If it not so much a question of repairing the valves if you put them in the concrete, but that it would be illegal to mount them below the rim of the tub.
  9. Bob's HandyGuy

    Bob's HandyGuy Senior Member

    Far be it from me to abet someone who thinks Terry's tub is ugly and something that resembles a horse trough is not, HOWEVER..... I've got 60 year old concrete laundry tubs that still hold water. (Wouldn't that type of surface be a bit abrasive, if the concrete were finished rough, or slippery if finished smooth?)
  10. abrasive bottom

    I thought about that abrasive bottom too

    I wasnt sure if this "hog trough' had a wood bottom

    to it or a concrete bottom.....

    it certanly isnt going to be a place where

    you and your girlfreind are going to frolick for hours in...

    skinning up knees, buttox , shoulders ect....

    I dont think this concrete box is
    going to be very appealing to the opposite sex either,

    maybe one time , but never again.....
    (unless they like it rough.)

    its certanly not going to be a "chick magnet"
    if you know what I mean..

    Terrys tub is a far , far better choice for my money..
    Last edited: Jul 2, 2005
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