Hello all,
I am in the midst of a DIY bathroom remodel. The forum/webpage have been a huge help! I removed a fiberglass shower and replaced it with Kerdi over new drywall and Kerdi over a mud pan. Passed the flood test (

) and am ready to start removing the existing flooring / vanity / fixtures.
The current flooring is 3/4" 1x8 tongue and groove plank, 3/4" plywood, and linoleum on top. That height matches up with the wood flooring in the hallway adjacent. I did run numbers through the Deflecto and the deflection passed for ceramic tile. There is a separate bathroom existing that has ceramic tile that also matches the wood flooring height - longer unsupported span but not exactly sure what was done between the tongue and groove planks. I think that tile is at least from the 1980s if not originally from the 1960s and has held up well so I am fairly confident the new flooring in the upstairs bathroom will hold up as well given a short span.
My plan was to cut out the 3/4" plywood to bring it down to the original subloor and then add a new layer of 1/2" plywood to minimize the height (figured it would be easier to cut the plywood out rather than try to remove adhesive off the face). Originally I was looking to put Ditra on top of that but realized 1x1 mosaic tile may not work on account of the 2x2 minimum size requirement. I have seen a few threads that say it is possible to prefill the waffles in but generally sounds like that is not recommended on account of the tile size.
I have been digging through the forum and it sounds like there are 2 options at this point but would appreciate any advice on what might be the best course?:
A) Add new 1/2" plywood to existing subfloor, then add 1/4" CBU with thinset between plywood and CBU plus fasten 8" OC, then thinset and tile over
B) Add new 1/2" plywood to existing subfloor, then install Nobleseal CIS / TS, then thinset and tile over
Option A has materials locally available which is a plus. The room is only 8x5 so it's not that large but I suspect it would be a stretch to get the demo portion done (plus some plumbing), add the new plywood, and add the thinset + CBU in a day (giving it 24 hours to cure before starting tile).
Option B I would have to order the material online which is fine as I have time to accommodate the shipping. Reading through the install instructions it sounds like if EXT or 21 Noblebond is used you can then install tile the same day? That would be a big plus as far as sequencing goes. Floor height would also wind up being pretty close to the existing height / transition which I would prefer.
I am leaning towards option B at this point but wondering if there might be any other options I am missing? It seems like B would be less work overall and I am guessing about equal cost as well by the time you compare the CBU sheet & screws to the membrane & adhesive.
I am also trying to minimize the amount of time the toilet and vanity are out of commission so even though the CBU option may not add that much extra time labor wise it's possible the plumbing might be out for longer if I can't get tile down the same weekend.
Any insight is much appreciated!
Thank you