Depends on joist or slab, and condition. Share photos

I forgot to say that. We are on a slab. Not sure what photos you need to see.

I just posted pics and answers, and nothing actually posted. Houzz issues are driving me crazy. I will wait an hour to see if my pics show up.

House was built in 1966 by previous homeowners. 800 sf lake cabin. Over the years they paid other idiots to add on to it. Now 3500 sf. To get a lakefront lot with a gentle, grassy slop to the lake, you have to fix the house that is already there, or tear it down. Most lakefront property here has 120 ft easements or 70-80 ft cliffs to the water. You buy based on the location. When we were looking to buy, we actually saw an even more chopped up home. I finally figured out that it was a small mobile home that they built around to add on to it. Strangest house I have ever seen.

The guy that added on to this house could not do math well. The garage floor is higher than the living room floor. Nothing we can do to fix that, but we can fix the bathroom floor, maybe.

Remove the old tile. The floor can be raised by using cement backer board with a thickness that works the best. You can use a crack suppression membrane like Ditra or Schluter.

You can then, if you are good, float a mortar bed and install the tile. You are still going to have some height issue but it won't be as bad as what you have right now.

Remove the tiles and start from scratch will be the easiest thing to do.

Durock's website says to install on wood.

But I found this info...

Manufacturer Recommendations

James Hardie Industries, makers of HardieBacker®, and USG, makers of Durock®, indicate that their respective cement backer boards should not be installed over concrete.

• James Hardie: HardieBacker specifications specifically exclude concrete as a base for installation.
• USG: Durock does not expressly exclude concrete, but the material is specified only for minimum 5/8-inch exterior-grade plywood or OSB. One source reports that USG will not officially validate the Durock-to-concrete attachment simply because they have not tested it. The lack of testing may be simply because so few customers express a need for applying Durock to concrete.

There is no problem with the two materials being compatible. The issue, as Bud Cline of The Floor Pro says, is more about how to attach the cement board to the concrete. A powder-actuated nailer is out of the question since nail depth would be impossible to regulate. Concrete screws, Cline says, have heads that are too small to hold down the cement board.

His recommendation: Work with the concrete surface so that it is strong enough and porous enough to accept tile mortar. Portland cement-based fillers can take care holes and cracks. Painted concrete can be sandblasted, sanded, or ground down to bring up a nice, porous surface.

Most tile professionals, including John Bridge, concur: Attaching cement board to concrete is not an acceptable way to surface the concrete prior to tile installation. Thin-set alone will not help the cement board stick to the concrete slab. Screws are the only logical way to do this, but it would entail an extremely tedious and time-consuming process of drilling pilot holes before sinking the screws. Additionally, you would be fighting against the thin-set bed under the cement board when drilling the holes and driving the screws.

The View of Tile Professionals

But the manufacturer prohibitions or omissions are warranty issues. The questions remain: Can you effectively pair two cementitious products—cement board and a concrete slab?

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I went to Wedi's website, and the foam panels CAN be used on concrete for floor tile.

Installation over concrete subfloors

Floor application for wedi Building Panel

All wedi Building Panel sizes and thicknesses can be used as tile underlayments over concrete subfloors. Modified thinset mortar, combed through with a minimum 1/4” x 1/4” notch trowel, will then provide a ribbed bed into which the wedi Building Panels will be laid. All joints should be staggered so that no seam continues throughout the length of the floor. Apply weights (i.e. tile boxes) onto the surface and where transitions are located while the mortar is setting up. After the mortar has set, wedi alkali resistant fiberglass mesh tape, or wedi Sealing Tape or wedi Joint Sealant should be applied to all seams, then tiling can begin.

So Wedi panels may be easier and faster for us to install after the marble tile is gone.

I also found a new floating porcelain tile product that Dal Tile started selling. It is like installing laminate flooring or vinyl planks.

Dal Tile Revo Tile - they said I could install it over the marble as long as I level the floor with self-leveling compound, including where the missing tile is. I still need to follow requirements per tile industry as to x " per 10 ft. I can't remember ... 3/16" or something like that.

https://www.daltile.com/revotile

$4.50 sf plus $25.00 for tools, $58.00 for 9 lbs of grout. Underlayment $54.00. Adhesive tape for seams. $542.00 and I can install it.

I am calling We Ship Floors tomorrow to see if their floating Supercore Extreme Vinyl Tiles can be installed over my marble once the floor is leveled. And if I can install over Wedi panels.

For someone who works with mud day in and day out, I am sure it is much cheaper, but I am afraid that I can't do it. Three more tile guys today told me wrong installation procedures for backerboard on the marble and for the tub surround, so I will not be calling them back. Just because they owned a trowel doesn't make them an expert on tiling,

I am not a tile installer, strictly wood only. But, you can build up the 1" differences in two phases.

Phase 1 - install a cement base like a scratch coat. This coat should be at least 3/4" thick. And should be fairly flat.

Phase 2 - install self-leveling cement for the remainder.

Your tile and thin-set should total 3/8" for small tiles. 1/2" if, you're installing larger tiles. 3/4" if, it's humongous. Adjust your ,math accordingly.

Thanks, G&S

current tile industry standards call for minimum of 1.25" at thinnest point of any screeds unbonded over plywood. w proper deflection and prep. 3/4" bonded over a slab.

Self levelers require deflection assessment and thickness considerations as well.

Id suggest you purchase A TCNA manual and limit your internet DIY search. Focus directly on The TCNA manual and manufacturers tech support to gain wisdom.

Mint Tile, thanks. I ordered a hardcopy book, but have not received it yet. I should have ordered a digital copy, but I like hard copy books. Kerdi did not say that their Kerdi boards would work when I checked out their website. Wedi's website did, but those boards are expensive. Plus, the concrete still has to be leveled and we can't work with concrete ourselves. There are many jobs that are NOT DIY and this is one of them.

Vocabulary/terminology is a problem. Even if I read the book, I will still have questions. I wish I could just trust an Oklahoma tile contractor to do the job correctly. All we have are "handy-men" who are self-taught and decided to call themselves "Pros". Or we have carpet and tile retail companies who train employees how to tile, then the employees leave the companies to be "pros" on their own.

It looks like I will leave the height difference alone and use a SPC click and lock LVT tile that says it will go over an old tile floor. (I may still remove the marble though.)

If I could find someone to tile the floor correctly, they could name their price. I have been looking since April, and I seem to know more than the local contractors do. That's sad since I don't know much at all.

I just got stuck buying another new tub $800.00 + labor costs of $1,800.00, since my plumber refused to read the installation instructions. The tub flange is now broken because of this "pro" who wanted to do the installation his way. I even handed him the instructions which he threw over his shoulder.

I am beyond frustrated. We usually don't do any DIY.

best of luck thats one city i dont have a tile friend in to refer to you.