Flooring Tile - Need Advice on a new installation

Hello all,
I have undertaken a rather extensive bathroom renovation project. The bathroom floor itself is small (80" x 64 3/4"), but what worries me is that the floor is hardwood (not tongue in groove, but solid wood). The tiles are 12" x 12" slate. I have heard and read a good deal of conflicting information as to how to go about installing this type of tile on this type of floor. I'm aware that the planks expand and contract at different rates, but I was wondering if a successful, long-lasting installation is possible on this type of surface. I have purchased hardibacker cement board and thinset to go over the top of the wood floor. I am completely new to this and would like as much help/advice/info as possible before I try anything. I don't know how thick the floor is, or if it has a finish that will prevent the thinset from bonding. I would greatly appreciate any help.
Thanks in advance.

If you are installing a ceramic type tile, you 1st need to have a minimum 1 1/4" thick sub floor under the tile. You can drill a hole in the hard wood floor to determine how thick it is. If you aren't sure that you'll get good adhesion between the wood and the thinset, then you can nail /screw A/C plywood to the hardwood. Coat the plywood with a flooring sealer/primer and then install your tile with the appropriate thinset.

If this is a "hardwood" floor, then it needs to be ripped up. I believe the thin strips of wood will have too much movement.

If this floor just happens to have hardwood used as planks (1x8's), then you should put a 1/2 of plywood on top of it, screwed to the planks, not the joists. Then thinset and screw the hardi down and then tile on top of that.

Be aware that natural stone requires a stiffer (stiffer than one for ceramic tile) floor to avoid cracks in the future. might be a good time to check your joist size, spacing and the span under the bathroom.

Thanks you guys for the advice. I appreciate you taking the time to respond to me. I am somewhat confused as to what you were saying JPicasso. How would I determine wheter or not my floor is hardwood as opposed to hardwood used as planks? I was considering ripping up the floor, but I dont have much carpentry experience. If I have to rip up the floor, I will but I'd like to avoid that if possible. Can you tell me how to tell the difference between the hardwood types and also, whats the optimum space for the joists. (I'm assuming joists are the actual supports for the floor.) Any feedback would be great.
Thanks

When I hear hardwood floors, I think of strip hardwood floors,
about 2-1/4" wide at varing lengths. However, usually (usually) these are
installed over a plywood or OSB base.
However, it may be that they used hardwood for your floor planking
that would be wide planks of wood either 8" or 6" wide?
(Wide planks would be fine, thin strips would not)

You also should check the stiffness of your floor,
Can you get to the underside of the floor?
We need to know joist size, (2x8's?, 2x10's?)
joist spacing, and the longest unsupported joist span under this bathroom.

If the floor is stiff enough, then 1/2" plywood, then cement board (1/4") or a membrane
and thinset your tiles.

You CAN install tiles on top of plywood as GeneralC suggested, but
there are preparations that need to be made, and I don't know enough
about that.

I apologize for not posting more quickly, I had to move a floor drain pipe to prepare for installing a pedestal sink. The floor is 1" thick solid planks with 1/2" thick small hardwoord planks I'd say 2" wide x 12" long. I can only see under the area where I cut out for the drainpipe. I don't know how helpful this information is, but the joists are 14" apart. The floor is very solid, but it does creak very slightly in one area near the door. I don't have the time/resources or ability to remove replace the floor. Would putting a 1/2" thick solid piece of plywood over the floor before I put the hardbacker down help my situation? If so, how should I go about anchoring it. Also, when all is said and done, this method will raise my floor roughly 1 1/2". Is there a danger to this? Any advice, alternate solutions or input would be greatly appreciated. Again, thanks in advance.

The 1 inch planking can stay. The finished hardwood floor has to go. These hardwood floors expand and contract way to much with the seasons and humidity conditions. Removing the hardwood flooring will solve some of your height problem as well.

After you have removed the hardwood check the planking to make sure all boards are in good condition and secured properly. Add additional screws and replace damaged boards if necessary. Then add 1/2" plywood exterior bc or better. The plywood should get screwed to the planking only. Avoid the joists as best you can. Leave a 1/8" gap between plywood sheets. You can use 1/4" hardibacker (the 1/2" will provide no additional strentgh to speak of). The hardi gets set in a bed of unmodified thinset and screwed to the plywood. Again avoid screwing into the joists. Use a 1/4" notch trowel for this. Use the square drive hardi screws designed for this. Leave a 1/8" gap between sheets. Tape the joints with alkali resistant mesh tape and modified thinset while you are installing the tile. The hardi tends to pull moisture out of the thinset so have a bucket of water and sponge on hand. Dampen the hardi with the sponge before you apply your thinset to the board.

Thanks all for the great advice. Each of you has probably saved me days of aggravation. I just have a couple more questions. When I lay the plywood, do I also leave 1/8" gap between the wall and the plywood or does it go flush to the wall? Also, what would be the best way to get those finished wood planks up? I just want to know the most effective way to get them up without damaging the floor beneath. Also, I'd probably have to saw them near the doorway, no? Any other thoughts/concerns you have on fixing the floor in general would be great. In any case, you guys have been amazing. Thanks for everything. :)