Under the bathtub: Durock or just subfloor?

Dear Readers, I'm renovating my bathroom: I removed the old cast-iron bathtub which was sitting directly on the wood subfloor. Im also removing the adjacent floor tile and its 1/4 plywood base, down to the subfloor as well. I plan to put down Durock and lay floor tile above that. Should I also put the Durock below the new cast-iron bathtub? Other than a minor increase in elevation of the tub, is there any reason why I shouldnt put Durock beneath the tub? All opinions appreicated. Thanks. -Theodore.
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On Jul 9, 3:15pm, snipped-for-privacy@yahoo.com wrote:

No reason you shouldn't do it and it would be good to do the whole floor with it, next best thing to a real mud floor if you can make the transition between the floor outside the bath. Install the tub, then tile the remaining floorspace up to the tub, caulk tub base with sanded caulk that matches the grout. Get all that 1/4 inch plywood crap out of there, make sure subfloor is sound and not rotting before you glue/screw the durock with durock screws (larger heads).
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On Jul 9, 4:15pm, snipped-for-privacy@yahoo.com wrote:

There's no real reason to have the cement backer board under the typical tub. I usually just run it under the front edge a couple or three inches so the tub is resting on it, and the rest of the tub is supported by the wood blocking attached to the studs.
In your case, since the tub used to sit on the floor, it's probably simplest to just complete the floor with the cement backer board. It's a good place to use up some of the larger scrap pieces.
What is the existing subfloor like? Diagonal shiplap boards are usually uneven and the cement backer board may fracture over a hump. It's generally a good idea to set the backer board in thinset when you're putting it down to make up for any discrepancies and fill in the voids so there's no movement.
R
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Yes, subfloor is diagonal shiplap boards. Thanks for the advice.
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On Jul 9, 9:33�pm, snipped-for-privacy@yahoo.com wrote:

leave opening for plumbing, think drain and room to work from below.
a friend did a exact job with cement board under his tub. years later he had troubles with no room to work.
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