bathroom tile query

[mikejurasw]

Greetings, (first post in a long time!),
I am strategizing for a bathroom re-do and need some advice about flooring. We live a 1920 brick home in Ohio, so my bathroom floors are a 3-4 inch deep mortar bed with small hexagonal tiles embedded. Over this, the previous owner laid (poorly) slightly bigger hexagons (the kind on a backer fabric), and I intend to hoe this up and start over. My questions are: since the original floor is not level (dips in the middle...I suspect a crack), how should I level it before laying newer, hipper tile? And, can I put down new ceramic tile over the old hex stuff with just mastic/thinset? (and is there a difference between those two?).
Any help will be greatly appreciated!
Best, MM

 

[oldognewtrick]

Is there by chance access to the floor joists from below the bath area so you could stretch a string to see if it's the structure that's deflected?

 

[havasu]

If the floors have highs and lows, and not structural like ol' dawg spoke of above, I would chisel out the old crap, then level the floor using SLC (self leveling compound).

 

[slownsteady]

I wouldn't tile over the old stuff. Bite the bullet and get the old floor out. Just how much higher can you afford the bathroom floor to be???
1/4" Hardiebacker makes a pretty good base for the new tiles