Bathroom Tile Question

What's the sub floor material? A concrete/hardiboard? Hard to tell from the pic.

Here you go.



I would try to clean up what you have, and if it doesn't satisfy you remove and replace the backer board.

Yea you should be good to leave it, just get up the old thin set as good as you can. As long as the cement board isn't crumbling/busted up or coming up. You could put some floor leveler or skim coat some thin set over some spots of cement board that chip up. I'm assuming it's pier and beam or an upstairs room. If the cement board seems like it's got a little bubble to it or soft spot, you can always throw some more screws in it to tighten it down because they might not have put thin set under the cement board when installing it.

Would that be odd on a second floor unit? I’m also not seeing any tape or screws