I'm in the midst of installing a new tile (marble mosaic) floor in my '50s era bathroom. I've removed the vinyl flooring and the 3/8" plywood (luan i think). What I'm left with is the 3/4" x 5 1/2" boards, which are nailed to the joists. My question is this... Do I need to install another layer of plywood over the planks as well as a layer of cement board before tiling or can I just go for the cement board over the planks? I'm inclined to think that I need both layers, but I'm afraid the two layers plus the tile will be way higher than the finished floor height of the adjoining hallway. Any advice is much appreciated. I think I've included all the details, but please feel free to ask any questions. I'm including a picture for reference. Thanks in advance.
Need the less height then get rid of the old subfloor, it's not doing you any favors.
Just use a Toe Kick saw to cut right up to the walls.
If you just go over it or remove it use 3/4" T & G Advantec subflooring then 1/4 tile board set in a bed of thin set.