URGENT - Wanting to use concrete board alongside existing ply

[Allysunlife]

I am repairing one square meter of bathroom floor which has gone rotten because of a bath leak. I intend to extract that section and replace with concrete board however the rest of the floor is plywood. Can this be done and how do i tackle the joint where the concrete board meets the plywood? I am not a professional tiler just a DIY enthusiast.

 

[eddcottee]

You shouldn't tile to ply, so the correct thing to do would actually be to lift all of the ply and replace the ply with cement board, then tile to that, assuming there is no "bounce" in the floor? Might aswell do it now whilst you're ripping the damaged section out.