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  • Tie the tub to the floor?

    I'm putting in a cast iron undermount style bathtub and have a question. The installation is a tub/shower in an alcove. The surround, tub deck and apron will be slab granite. The tub is a Kohler K-850, which is designed to be either drop-in or undermount. It's about 250 pounds.

    The installation sheet that came with the tub says that the tub should be setting directly on the floor, levelled with metal shims. The tub will be framed around, and a piece of 5/8 ply, with a cutout for the tub and the tub rim set flush to the top surface of the ply. The ply is the substrate for the granite slab deck (same as a granite countertop). The rim around the tub will be polyurethane'd to the underside of the granite.

    I live in earthquake country (CA) and once in a while we get a pretty violent shaker - maybe enough to toss the tub up off the floor a bit. Being an undermount, the granite tub deck will capture the tub and keep in from jumping vertically. But the tub deck, with that huge hole in it, is pretty thin around the periphery. Being brittle granite, seems to me like it might crack easily.

    So here's the question. Seems like the tub should somehow be secured to the floor to hold it down rather than rely on the tub deck to capture it. Do you guys have a way to hold the tub down to the floor? The tub's bottom feet are very, very short stubs - there's no way to drill a hole and get a mounting bracket on them.

    I was also wondering how the freestanding clawfoot tubs work? Wouldn't they jump around in an earthquake and break the water supply & drain lines?

    Am I worried about nothing? Thought I better ask before doing anything.

    Thanks (yet again),

    -Andy

  • #2
    Re: Tie the tub to the floor?

    Spray foam (the Great Stuff sticky brand) might adhere to it and the floor. Then urethane/silicone caulk between the granite and the tub (it is undermount, right?) could provide some cushion.

    I think you might be worried for nothing. But I've never been in an earthquake either.

    J.C.

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    • #3
      Re: Tie the tub to the floor?

      >> "I think you might be worried for nothing. But I've never been in an earthquake either."

      Never been in an earthquake?? Well, coun yourself lucky. We have them quite frequently here. Most are so slight they are barely noticeable or not noticeable. But once in a while we get one around a 6-1/2 or 7... fairly exciting. You probably have hurricanes or tornadoes where you are.... I've never been through that.

      Not sure the foam would do a heck of a lot... those big quakes get pretty ornry. Not hearing anything from CA folks on this topic... maybe I am worried for nothing.

      Thanks for your comment!

      -Andy

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      • #4
        Re: Tie the tub to the floor?

        Most tubs get set in bed of mortar this is to support the tub floor and keep it from sliding. I would definitely set it in mortar. I don't think there is much you can do for the up and down motion though.

        Seems like the best thing is to use a flexible adhesive on the granite. Bend don't break philosophy.

        I have been in an earthquake but I was 5 and don't remember.

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        • #5
          Re: Tie the tub to the floor?

          I'm a Marin Co. G.C. I do Earthquake Retros. and all My own plumbing.
          I would never bother to worry about Anchoring a C. I. tub! I wrap the sides with R- 13.
          My Struct, Eng. had 28 Years with Bechtel. He's the one that told the City to save or Demo. Buildings after the North ridge Earthquake. He's never spect. tub anchors!
          I can build anything You want , if you draw a picture of it , on the back of a big enough check .

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          • #6
            Re: Tie the tub to the floor?

            >> "Great choice in tubs. Cast iron rules."

            Thank you! I really, really, really don't like acrylic tubs. They look good for a while.... but c.i. looks better (my opinion) and you don't have to worry about the finish getting scratched or dulled due to cleansers, etc. Plus it has that old school charm.

            >> "Never saw a ci tub damaged....the whole house cracked in half, but the ci tub was fine...."

            I'm not worried at all about breaking the tub, it's pretty stout. My concern is that since it's undermounted, if quake hits it will break the granite tub deck. Granite is great stuff but it's very brittle. Plus f you think about an undermount tub deck, it has the enormous hole in it and actually the remaining granite edges aren't very wide at all.

            But I'm coming to the conclusion that there isn't anything that will be very effective for this with my tub. Kohler didn't design in any provision for structural fasteners at all, except some cast-in reinforcing gussets.... and if I drill a hole there and the porcelain chips due to vibration from the drill then I'm out quite a pile of loot.

            I end up buying a lot of Kohler stuff (my real boss likes the look) but in general I'm never too impressed with the mechanical design. The cast iron and porcelain work is nice, though.

            >> "Most tubs get set in bed of mortar this is to support the tub floor and keep it from sliding."

            I've seen acrylic tubs commonly set in mortar, but never cast iron. Is this commonly done on iron, too? I make a wood frame out of 1x4 that fits tight to the mounting feet and is screwed through to the subflooring to keep the tub from walking. Maybe the mortar is the way to go, though.

            >> "I'm a Marin Co. G.C. I do Earthquake Retros. and all My own plumbing. I would never bother to worry about Anchoring a C. I. tub! I wrap the sides with R- 13."

            Well, we're neighbors... so that's good to hear. Thanks for the tip on the insulation. I'll definitely do that!

            Thanks for the advice, guys!

            -Andy

            Comment


            • #7
              Re: Tie the tub to the floor?

              Some Tubs if set in Mortar will void the warranty.

              Read the specs and install instructions for your Tub model.

              If a quake is gonna pop the tub nothing you can do will prevent it, I gotta agree with JC.

              If you are talking about a 7.0 quake your home will not be standing anyway

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              • #8
                Re: Tie the tub to the floor?

                >> "If you are talking about a 7.0 quake your home will not be standing anyway."

                This is CA... the house has been through a 7 in 1989 with no problems... thank goodness for structural codes. I've personally been through two 7's in CA, the '89 and one in So. CA in 1969 when I lived there. Lots of broken items, but no structural damage in either case. California wood frame homes (except those on a slab) are flexible and move around a lot but most generally come through pretty well up to a 7. Worst damage I've experienced is some minor cracks in drywall. Some people had it much worse... where your house is relative to the waveform of the motion has a lot to do with it. Masonry, brick or adobe homes had big problems. But generally making it through a 7 with a flexible CA wood frame home is fairly common. Don't know about an 8. It's a logarithmic scale so the energy in an 8 dwarfs a 7... and they say we're due for a "big one".

                Up the hill from me in the '89 quake there was a tract where the builder didn't bolt the homes to the foundation (a code violation). Several of them jumped right off, and were total writeoffs. There's a good bit of vertical force. The ones that were tied down (like mine, fortunately) did ok. Hence a big part of my concern about just resting the tub on the floor. That just doesn't sound right to me. But apparently it's standard practice.

                Tub instructions from Kohler don't say to set the iron tub in mortar, just to level it with metal shims under the feet. The installation sheet says nothing about the warranty either way.

                Thanks for the comment! I don't think I'll be using mortar, probably just install it "normally" and look into earthquake insurance!

                -Andy
                Last edited by Andy_M; 05-24-2009, 05:34 PM.

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                • #9
                  Re: Tie the tub to the floor?

                  I would set the tub exactly how Kohler's instructions say to. The tub will not move during an earthquake and if it does the surround is history anyways.

                  Mark
                  "Somewhere a Village is Missing Twelve Idiots!" - Casey Anthony

                  I never lost a cent on the jobs I didn't get!

                  Comment


                  • #10
                    Re: Tie the tub to the floor?

                    You're just down the road,what the heck. I'll bring over My mag drill. I figgure 2- 5/8"
                    holes in the bottom and some 8" legs should keep it honest.
                    Toll free phone # 1-800,EIEIO
                    I can build anything You want , if you draw a picture of it , on the back of a big enough check .

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                    • #11
                      Re: Tie the tub to the floor?

                      Originally posted by Andy_M View Post
                      Do you guys have a way to hold the tub down to the floor?
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