Backbuttering mosaicsSometimes I  get asked how to backbutter mosaic tiles. I constantly have to tell people that you really don’t need to. There are very few instances when you’ll need to backbutter a mosaic tile. Normally if you feel the need to backbutter mosaics it is easier to simply use a larger trowel on your substrate.  

Backbuttering mosaicsIt is, however, a very handy thing to be able to do when needed. In the case of all these photos I chose to backbutter, or more pointedly put the thinset on the back of the tile rather than the substrate. The width of the niches these mosaics were going into was smaller than the size of my trowel, which makes it difficult to properly comb thinset on the back of the niche.

To backbutter mosaics simply grab a scrap piece of your substrate, in this case it was kerdi-board, and comb the thinset onto it just like you would if you were installing the tile to it.

Backbuttering mosaicsThen place your mosaic sheet into the bed of thinset and push it back and forth into the thinset, again, just like you would if you were installing it.

Once you get it bedded properly, peel the sheet of mosaic off of the scrap piece of substrate. You’ll have a sheet of mosaic with thinset fully covering the back of every tile in the sheet. You can then just install it wherever you need it. 

If you are using translucent, or semi-translucent glass mosaics, which is simply big words for stuff you can see through, be sure to flatten the ridges in the thinset first so they are not seen through the mosaic.

Backbuttering mosaicsThis works well in the back of niches, small areas that need mosaic, or anywhere else it’s difficult to stuff a trowel full of thinset into. It also ensures complete coverage if you are doing something like placing mosaic tiles on the ceiling of a shower.

In the few instances you actually need to have thinset on the back of a sheet of mosaics this is a very handy trick to have in your bag.

You can click on any of these photos for a full-size example of my horrible photography skills…


Backbuttering mosaics

Fully backbuttered mosaics

Backbuttering mosaics

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  • greg

    I am considering installing a 6ft x 2ft x 3/8in slab of marble for in front of my fireplace. I am a happy ditra user, but was also interested if you have any recommendations for the underlayment as i have not laid marble before. I appreciate you wise (ass) words and you have helped me tile an entire bathroom complete with tub to walk in shower conversion (all schluter products). Thanks for your time.

    • Roger

      Hi Greg,

      Since it a single slab you can use nearly any approved underlayment in that application. I would likely use cement board there, no real need for ditra or anything like that with a single slab.

  • Arnold

    Previous: “It also ensures complete coverage if you are doing something like placing mosaic tiles on the ceiling of a shower.”

    What is the best technique for keeping the mosaics on the ceiling?

    • Roger

      Hi Arnold,

      Comb the thinset on the ceiling, backbutter your mosaics and place them up there, then pound them in firmly with your grout float.

  • Mike

    Excellent site. I am planning a black and white herringbone pattern for the bathroom floor. I want to use black grout for the black tiles and white grout for the white tiles. Is there a method to separate the spaces between the tiles and use one grout color at a time?

    • Roger

      Hi Mike,

      You can just use painters tape. Do the black grout first! You can get white grout off of black, you will never get black grout out of white.

  • TheCaptain

    Hello Floor Elf,

    This is a question separate from this post. Oh yeah, and thanks for the books, they have answered several questions I had, but raised at least one:

    You mention that I should not lay 2 x 4’s (wood, whatEVAR dimension) directly on concrete because the wood will absorb moisture from the concrete over time. So I have a concrete floor and I need to build a partial wall along one side of the shower (the top portion will be ludicrously expensive glass). Two sides are ‘walls’, one side is a half wall (sink on other side), one side is Kerdi-curb. Here is some ideas I have had, but need the Expert Elf:

    Can I paint the concrete under the partial wall?
    Use a piece of Kerdi membrane along the bottom edge of the 2 x 4?
    Use Red Stuff (please say no, I don’t have any and don’t want any)?
    Other ideas?

    Your books are very useful, and as I said, I’m all over them. Using Kerdi including a kerdi shower pan. I’m not made of $$, but this really did seem to be the best option given that I have SOME money ;->

    Fair Winds

    Cap’n Jan

    • Roger

      Hi Jan,

      If you are building a 1/2 wall you can put pressure treated dimensional lumber directly on the concrete. It will not move enough to affect any tile. The ‘no wood on concrete’ is for building a curb where the lumber is the only thing in the curb, and it’s solid so no room for ANY movement. With a 1/2 wall it’ll be fine. You can also use kerdi or the red stuff. :D

  • Chief Steve

    I want to thank you for this tip. I have been noodeling how I was going to be able to set my mosiac 1″ hex tile in the small space between my tub and the wall. It is a rounded corner tub and tapers to within 1″ of the wall, clearly to small for even a putty knife. I considered trying to cut notches in a plastic trowel, but I think this solution beats that approach.

  • Wendy

    Thank you, thank you, thank you! This technique was amazing to use in an area it was difficult to get a trowel in without making a mess everywhere. Every other website said to back butter with the trowel, but i found it was hard for me to do this without pushing a lot of grout through the mesh and up into the tiles. I am redoing my bathroom, and your site has been invaluable to me. Thank you.