A 1/2" trowel is recommended for 6x36 tile - can i use a 1/4" trowel to minimize the finished tile height if tiles are fairly flat and can get 95% coverage?

This is for a curbless shower. Also the bathroom floor has been leveled.

The finished shower floor tile is a 1/2" above the bathroom sub floor. The bathroom floor 6x36" tile (i plane to lay next to the shower tile) is 3/8" including the square grid pattern on the back side.

I'm afraid that if i use a 1/2" trowel, the height of the 6x36" bathroom tile next to the shower tile will be too high next to the shower tile by about 1/4" especially since I'm using the the Rubi Level Quick system.

The Rubi strips have curved feet that do not fully flatten out under the tile imposing a minimum space of slightly under 1/8" (about 3/32") under the tile.

I was thinking that i could use a 1/4" trowel and maintain a 1/8" mortar bed under the tile with thicker back buttering and since the Rubi Level Quick strips impose a 1/8" space under the tile anyway. That should keep the height difference between the shower floor tile and the bathroom floor tile to a minimum.


  • I sounds as though you are doing a curbless shower?
    – Jack
    Feb 27, 2022 at 19:04
  • yes, a curbless shower. I added some text to the end of my original post to further explain the situation.
    – nelsonm
    Feb 27, 2022 at 19:25
  • also, the bathroom floor has been leveled.
    – nelsonm
    Feb 27, 2022 at 19:35

2 Answers 2


A 1/4in trowel applied at a 45deg angle will not leave you a 1/8in space but less, about 3/32. (Theoretically 0.25 x 1/2 x 1/sqrt(2)). If this is the height of the levelers' feet, you have no margin for unevenness.

To get 1/8in sufficiently broad for 95% coverage, you need to "double butter", i.e. apply the tinset to tile and also to floor before placing the tile.

This provides the best bonding anyway. Use the "keying in" technique. Work it in for a good bond, then scrape it off.

Just spend focused time on each tile. Small area, no need to rush. Place it, remove it, check, re-scrape, place, tap. If the floor is smooth and adequately levelled already, then 1/4in trowel is fine and to double butter you could trowel the floor side, and apply flat on the tile back.

In your case this might be a workable compromise. The coarser trowel recommendation for larger tiles has to do with dealing with the larger total floor unevenness that may occur under a single tile. The larger the tile, the larger the total difference can be, and the larger any voids could be.

Double buttering will also help offset this issue, not just because of the extra thickness, but mostly because any lower spots are still covered and ridge tops will come in contact with the opposing tiled side.

What works in your favour is that you are tiling a shower floor, not a commercial entry. Even if you do not achieve 95%, it is very likely adequate. Heavy hard items are not commonly used in the shower, and do not use a sledge hammer for showering.

  • the bathroom floor has been leveled.
    – nelsonm
    Feb 27, 2022 at 19:37
  • yes, so your risk is even lower. Just spend focused time on each tile. Small area, no need to rush. Place it, remove it, check, re-scrape, place, tap.
    – P2000
    Feb 27, 2022 at 19:39
  • Thanks, the shower floor is already tiled and has the 1/2" height edge off the bathroom floor. It's the bathroom floor I'm tiling that the question is about.
    – nelsonm
    Feb 27, 2022 at 19:52
  • ok sure, still relatively small area I'd think, in the sense that you can spend some DIY time building deep core muscles in trial-and-error, and keeping a close eye on levelling and coverage. Good luck with the project!
    – P2000
    Feb 27, 2022 at 20:09
  • thanks for your support and info.
    – nelsonm
    Feb 27, 2022 at 20:59

The trowel size spec is there for a reason, if you use a smaller notched trowel, especially when using the Rubi clips which will lift some and lower some tiles. The concern would be the ones that are lifted. You should be able to imagine why.

Most showers have a curb to keep the shower water retained where it should be, this hides the differences in the floor heights. If you are doing a curbless shower, if it were me I would prefer a slight height difference to act as a very small curb. One that could keep a small level of water contained should the drain not accommodate the water entering the drain for whatever reason.

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