I am tiling on a concrete slab which is flat but tilted, and I have just less than 1/2in to fill, at the lowest point.

To compensate for the tilt, should I

  • apply adhesive cement on both tile & surface, with a 1/2in notched trowel, or
  • fill & level with cement first?

Tiles are 1' x 2'. The affected area is about 50 sqft (about 25 tiles)

The picture shows my levelling lumber along the top of the tile surface, a loose piece of tile, and the gap, with a 1/2 notched trowel for reference.

enter image description here

  • Are you using backer board on top of concrete? – Ed Beal Feb 15 at 17:35
  • @EdBeal, no but that's maybe an idea to fill. What were your thoughts? – P2000 Feb 15 at 17:57
  • I would use a mortar bed to fill was the tilt for drainage? That would be by only concern , I was using my phone and the resolution’s not the best with the shadows but a bed of mortar will stick well to the existing slab make sure to wet it down first, sometimes if the concrete is really slick I will acid etch with muriatic acid or pressure wash to provide a better surface then lay a layer of mortar let it set and continue tiling. – Ed Beal Feb 15 at 18:23
  • Awesome @EdBeal. The concrete is rough. There was no drainage. But now I'm curious: what would the backer board have accomplished? – P2000 Feb 15 at 19:11
  • I thought you were using backer board and that would have been my question to you. We bought a bank repo that the owner thought he knew how to do tile, yup you guessed it tile on backer, the first freeze it started buckling was great for us got the place for 10 cents on the dollar. It looked like land mines had gone off everywhere. – Ed Beal Feb 15 at 19:13

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