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Subfloor under Cast iron tub?

I am replacing a 1920? freestanding claw foot tub with a new TOTO cast iron tub with apron. I believe the weight of the new tub is about the same as the old claw foot tub. The subfloor is 3/4" thick 3-1/4" width tongue and groove 100 year old redwood. After removing the layers of vinyl and linoleum the subfloor appears to be in good condition. The framing is 16" OC. I need to shim the new tub about 1/2" on 1 side to level it.

Do I need to put a piece of structural plywood above the existing subfloor? I will be tiling and using cement board as the under layment for the tile. I don't want too much of a step at the transition from the hallway. thanks.

Re: Subfloor under Cast iron tub?

You'll need to find out if the floor joists can handle tile. 3/4" CC grade plywood is ok for joists 19" or less on center. Head on over to the John Bridge Tile Forum and use the handy dandy deflecto-lator linked in the dark blue bar and plug in your information.

The fine folks on the JBTF can help you with every step of the remodel.

Re: Subfloor under Cast iron tub?

After you verify that your joists are OK with the new weight (you need to know their size and span), do the math: tile (about 1/4") plus CBU (about 1/2") - will give you a total of about 3/4" plus the thinset. If you want your tub elevated a bit, lay 1/2" under it, shim it and the new tile will only be about 1/4" higher than the base of the tub.

Make sure your plumbing allows it.

Re: Subfloor under Cast iron tub?

Thank you Houston and dj1. Thanks for the reference to the calculator at the John Bridge site, I'm in good shape with the weight, and I think I'll lay the 1/2" under the tub and shim it.
Thanks so much for your help.

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