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Looking to tile a basement landing as a transition from the stairs to the main room. The main room is done with DMX 1-step, 5/8 OSB and laminate flooring, so there is about 1.5" between the top op the laminate and the concrete slab. Approx 60 sq. ft in an "L" shape.

By my measurements, the new tile + thinset will accounts for ~1/2". Assuming an uncoupling membrane, if used, will add negligible thickness compared to anything else going down, I still have roughly a full inch to raise the concrete so that the tile is level with the existing floor.

Option 1: self-levelling concrete seems to be the defacto recommended solution for this. I'd rather not go this route because in my experience this stuff is finicky, the area is large enough that it will be fairly costly, and awkwardly shaped to make mixing, pouring and spreading difficult.

Option 2: some sort of cement backer board? From my research, manufacturers recommend not using these over concrete, but maybe someone has tried this with decent results?

Option 3: concrete topping or mortar mix? From what I've read, concrete topping this thin is not a viable option, but I saw a comment somewhere that the same mortar mix as used for shower pans might work. This route I could also possibly get most of the way there with concrete/mortar and then finish off with a thin layer of self levelling concrete if it makes sense to do so.

I considered the same subfloor (DMX + OSB/plywood), figuring that was the easiest option, but DMX customer service said it was definitely a bad idea.

Any recommendations or ideas on how best to tackle this?

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  • why the osb layer?
    – Jasen
    Commented May 13 at 0:43
  • @Jasen perhaps the laminate is a glue-down type?
    – Huesmann
    Commented May 13 at 11:35
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    OP, I don't see why cement backer wouldn't be useable. You'd have to figure a way to lock it in place. Maybe thinset on the concrete and CBU on top? You probably need about an inch of thickness, though, so you may need two layers of CBU.
    – Huesmann
    Commented May 13 at 11:42
  • @Jasen all the finished rooms have a layer of OSB. There's a workshop that I just painted and sealed the OSB as the final flooring and a bedroom that has carpet over the OSB. The laminate didn't strictly need the OSB, but the decision was made before we chose the floor to give us options (some thinner laminates require OSB, so doing it gave us options) and to have (almost) everything level, but DMX have specifically recommended I don't do this under the tile. Commented May 13 at 21:33
  • @Huesmann that's what I figured but all the manufacturers seem to specifically state that their boards aren't recommended for installation over concrete, but I don't know the reasoning behind that. Commented May 13 at 21:40

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