I recently taped my Hardiebacker boards with alkalai resistant tape and applied some thinset mortar over it. However, I'm a bit concerned that I laid it too thick. If I put a 12" x 24" tile over one of the seams, it definitely rocks back and forth a bit. I know that large format tiles like that will typically rest on a thicker bed of mortar, so it should account for any of the seams, but i'm concerned about it nonetheless.

The mortar is feathered out to about 6" on either side of the joint. It's not as smooth as I had hoped and I'm also worried it will make getting a good, even comb hard to do. Should I take the time to smooth out the joints with a stone before tiling?


1 Answer 1


I think you will be fine. As you pointed out, the thinset under the tile will offset any uneven bump in your subfloor. An even comb of thinset isnt required. whenever you press down the tile and level it, the thinset will move under the tile to compensate for any bump.

Usually i only put just a little between the hardiboards just to fill the gaps. Having a perfectly flat subfloor is not necessary.

  • Yeah, a tile of that size calls for at least a 1/4" x 3/8" trowel notch. That should accommodate just fine. You could always tilt the trowel more over the humped joints to lower those areas
    – isherwood
    Commented Jul 16, 2019 at 15:54

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