I want to tile a concrete floor that has 1950s tile already installed on part of it. The problem is, one edge is out of flat with a slope change of almost 1" in the last 2 feet. Other than that slope change, the sections are individually flat. The slope change is where the previous owner apparently put leveling compound to overcome some defect in the slab. The compound and the slab are stable and have been for years.

I planned to use a 1/4" slip sheet over the whole floor, and use smaller tiles that may be more forgiving to the slope change. If I apply more leveling compound I can move that 1" slope change to be over 4 or 6' versus the last two feet, but it's too much compound to cover the whole 24' room I think.

What do I need to do before I lay tile?
Ive added a sketch. Im not certain of the make up below the leveling compound, but there is certainly a footer in there. I also have concern disturbing the old likely asbestos tiles. enter image description here

  • Do you mean that one edge is 1 inch higher, or 1 inch lower than the rest of the floor? Is there anything underneath the floor?
    – kaya3
    Aug 26, 2021 at 9:47
  • Is there any reason to not simply fill (assuming it's a dip) the 1" change with leveling compound? There'd be no reason to cover the whole floor. If it's a 1" rise, you could grind it down (though that would be messy).
    – FreeMan
    Aug 26, 2021 at 15:20
  • 2
    It's not really clear what you're asking. You propose reasonable solutions to the problem. What's the question?
    – isherwood
    Aug 26, 2021 at 15:22
  • Judging by the words " the previous owner apparently put leveling compound", it seems the slab is slopping up towards the edge. I think the easiest way is to chip out the excessive topping at the affected area and re-level.
    – r13
    Aug 26, 2021 at 17:41

1 Answer 1


Ended up removing the existing leveling concrete, putting down primer, then adding a poured leveling compound, then a Ditra decoupling membrane, and finally tiling over the top. here is a better pic of the starting surfaces: enter image description here

And then the leveling compound (notice the green laser helping us maintain the gravity level of the compound): enter image description here

And Finally, DITRA decoupling membrane, thinset and tile above. enter image description here

One final note, the we used kerdi band strips between the DITRA orange pieces to "seal" them together, and even the very thin fabric bands caused us difficultly in final tile leveling where the bands were. In the future I would not use the Bands, or find a much thinner product if one existed.

  • When you apply the kerdi bands you only need to leave a minimal amount of thinset as to not cause a hump. What size notch trowel did you use? Also consider leveling clips for faster leveling of tiles for newer installs
    – redlude97
    Nov 29, 2021 at 18:37
  • I didn't use a notched trowel for the bands, but a flat one, I scraped as much thinset as i could both underneath and over the bands and they still raised the final mortar bed for the tiles by about 3/32ish which caused difficulty in getting the tiles level the ones on each side. they "tetertotterd" about the band in the middle. I did not use leveling clips, which basically pull up the tiles to level with each other?
    – mark f
    Nov 29, 2021 at 19:13
  • what sized trowel did you use to install the tiles? They look like 12x12?
    – redlude97
    Nov 29, 2021 at 19:17
  • I used a 1/4" x1/4" and yes they are 12x12... . I also back-buttered the tiles for better adhesion.
    – mark f
    Nov 29, 2021 at 19:25
  • 1/4x3/8 or 3/8x3/8 may have been a better notch size if the tiles were rocking, maybe even up to 1/2x1/2
    – redlude97
    Nov 29, 2021 at 19:36

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