[jyl]

Ok, still on the project old house conversion to cafe here.

Bathroom is 5’ x 5’ roughly. Pulled out old tub, toilet, vanity, walls, floor, so it’s studs and old 3/4” diagonal wood board subfloor over joists. Spending quality time in the crawlspace (bathroom was built as a bumpout, outside of the house foundation) blocking the joists, may add a couple piers and posts if needed. But that won’t make the floor perfectly level, just solid.

Want to tile floor with large hex terracotta (some reasons for that aesthetic choice, won’t go into it here).

Question is how to prepare the floor for tiling. City requires a floor drain. If they see a floor drain, you know people (dumb people) will treat the floor as if it is waterproof. So I want to make the floor waterproof.

I’m planning to use Ditra membrane and Kerdi tape. Yeah, like a shower. That’s kinda for my own education - I’m going to basically build a shower pan and want some experience with this “new fangled” stuff (I last tiled a floor and shower when Clinton was President, it was all cement board and poured concrete shower pan then).

Question: would you keep the old subfloor, screw down 1/2” ply or 0.4” Hardie then apply self leveling? Or would you cut out the subfloor, add blocking around the perimeter of the room, shim the tops of the joists level, then screw down 3/4” or 1” OSB? Would you cut the 3/4” or 1” into pie shaped sections and shim to slope the floor to the center floor drain?

Assume you’re me, trying to do a good job for a building we’ll keep a long time, what would you do?

P.S. Next I have to do this to the kitchen, which has lots of floor sinks and floor drains. And that is over the finished basement, so it *really* has to be waterproof. So I’m kinda using the bathroom as a learning experience for the kitchen.