We are updating the bathroom in our old house and after removing the old tile and concrete we found that it was sitting on 3/4" subfloor planks, and some of them are not in the best shape. We are planning to use Ditra or Ditra XL depending on the needed thickness for the underlayment. We have 1/4" porcelain tile (size 12"x23"). The gap between the old subfloor planks and the hardwood at the transition point is 1-1/2".
- The planks have quite large gaps between them in some spots, will this be a problem?
- How thick should the total subfloor under Ditra and Ditra XL be? Would the old 3/4" planks with another 3/4" ply (at least) be enough?
- What would be the best option to get to the same level as hardwood (1-1/2")?
- For example: add 3/4" ply + 1/4" ply + 1/8" Ditra + 1/4" tile
- Or: add 3/4" ply + 5/16" Ditra XL + 1/4" tile
Both options will be ~ 1/8" shy from making a perfect transition. Maybe there are better options?
- Should we glue (carpenter's glue) and screw additional plywood or will screws (grid pattern 4"x4") be enough?
Photos of the floor: