WE are remodeling our Upstairs bathroom and our contractor is saying to remove the 1/2" mortar that’s under our tile floor and put hardibacker instead? I don’t want a crappy job, which way do I go?
Absolutely remove the mortar! Hardie board or cement board is the way to go. Ask your contractor if he would also glue the board to the subfloor. We usually use thin set or liquid nails (troweled) for that installation method.
Hope that helps!
In an upstairs bath or any surface that will shift or move throughout the years, you will want to put down a Detra floating mud slab… Detra is a pitted plastic and vinyl underlaiment that must cut into place and trowel filled smooth with thinset so it acts as a single floating slab… Then you may trowel your mud bed and set your tile… If you have wall tile conjoining your floor tile? Use acrylic color matching grout… 
I would definitely remove the motor and put Hardie board or saludar Detra either one is good. This is standard procedure when applying ceramic tile to wood.
Yeah, like others have said, Hardie board is the way to go.
Good luck on your Remodel!