Flooring Tile - Help! New Stone Floor and Shower - Sloped Surface

I was forced to remove a marble bathroom floor in order to install a new shower. I removed all the old mud and lathe down to plywood. The drain has now been installed and I'm staring at what I know to be a very uneven floor -the building was built in 1871. The old floor (surface is 7.5 feet by 8.5 feet) had a 2X2 separating the room with a tarpaper, then a metal lathe on plywood, thenwhat may have been gypcrete poured to the top of the 2 X 2, then an inch of mud then marble. It was 3 1/2 inches high. I can't go that high again because of ceiling height restrictions. So my questions is: Should I use a diamond metal lathe on top of the plywood, then a leveler for up to an inch then a membrane thinset and marble? Any suggestions would be greatly appreciated. Thanks!

The floor's strength will come from the plywood and if you can add an additional layer of plywood at least 3/8" bc or better exterior grade, then self leveler will make a stronger floor. You need to prime the surface with the brand matched primer to the self leveler you are using, reinforce ti with 2.5 diamond lath secured to the floor and the pour should be no less than 3/8" thick when going over plywood. Be sure to dam the perimeter of the room and around stationary fixtures such as you tub or shower and toilet flange so there is room for seasonal adjustments of these things before you do your pour. Not only will the plywood make a stronger floor, but will be alot cheaper and lighter on your framing members. You will need 1 1/2 bags for each 1/8" build up, or 5 bags sust for the minimum build up of leveler, plus whatever amount is needed to make the floor level, so you are talking 300 lbs or more and $30/bag vs the cost of plywood. You would not need a membrane over the leveler if poured over the entire surface.

What do you think about using furring strips under the plywood if I need to build up more than 1/2 inch on one side. If properly fastened under the plywood before the leveler, do you think that might cut down on the thicknes of the leveler? Thanks again for your advice! :)

FUrring the plywood could create even more issues, especcially with stone since you need a floor that is twice as solid as you would need for ceramic. Just build up the floor with plywood, minimum thickness is 3/8" for plywood in a ceramic floor sandwich, but pic a thickness that will allow at least a 3/8" pour at the thinest location. If 3/8" plywood willnot allow that, then just use the self leveling cement. Now if you can build up the floor at it's currently highest level with at least 1 1/4" build up, we can walk you through doing a mud bed which will be very inexpensive and will provide the best possible setting bed.