Preparing the subfloor for tile.

Need some guidance on preparing a floor for tile.
I'm am currently remodeling a medium sized second story bathroom in a home built in the early 1900's.
Here’s the Low down.
I demo'd the room down to bare bones including pulling up the subfloor exposing the 2X6 Joyce’s on 16 inch centers. I installed 3/4" T&G plywood subfloor. The floor has a pretty noticeable sag to it (3/4" to 1") at its worst.
Now for the questions at hand.
Will self leveling compound be enough to fix this and be suitable for 12X12 tiles?
Also I plan on using a concrete backer board, what thickness do you recommend for best results and would I use the leveling compound before or after I install the concrete backer?

 

Gee wiz, kinda late now, you should have fixed the subfloor/joists system before covering it up again. Did you only screw the plywood down? Can you take it up?

Jaz

 

Are you sure your floor joists are 2x6's? What is the unsupported span of the floor joists? This is the measurement between supports from below.

 

Johnny the floor Joyce’s are 2X6's with about a 115" unsupported span.

Jaz yes I did screw the plywood down and the room is only about 3/4 covered in plywood so pulling up the 4 sheets of subfloor is still a fairly reasonable option however I am not convinced is my only one.

 

You floor joists as is will not support a ceramic tile installation. You either have to shorten the span of the joists by adding a support beam or sister the existing joists. Other options might be vinyl flooring or carpet.

Adding plywood and cement board will not change anything and self leveling compound is not an option.

 

Yea, that floor is too springy to leave as is. You should stiffen the joists, you need to fix the sag anyway, do both at the same time by sistering new joists to the old. It'll be pretty easy if the room is rectangular and it sags in the center roughly.

What other option were you thinking of?

Jaz