One of the most frequent questions I get asked is ‘What size and type of trowel should I use for…?’  The proper answer to that is ‘whichever trowel gives you the proper coverage for your particular installation’.

So there really isn’t one perfect answer to that question, a lot of factors are involved. But I’ll try to help you out.

Proper thinset coverage

The first thing you need to know is what constitutes proper coverage.  As stated in ANSI A108.5 3.3.2 for installation of tile on floors; “Average uniform contact area shall not be less than 80% except on exterior or shower installations where contact area shall be 95% when no less than three tiles or tile assemblies are removed for inspection. The 80% or 95% coverage shall be sufficiently distributed to give full support to the tile with particular attention to this support under all corners of the tile.”

Let me translate that for you:

Proper coverage of any tile in a dry area (bathroom floors, backsplashes, fireplaces, etc.) is 80%. Proper coverage of any tile in a wet area (showers) or outdoors is 95%. This includes complete coverage beneath all corners of the tile. You check this by installing a tile, then removing it to check the CONTACT of the thinset on the back of the tile. If, after checking three different tiles in three different areas of the installation, you have that percentage of coverage then you have proper coverage.

Example of Full Coverage

Correct complete thinset coverage

Always aim for 100% coverage. More is always better. The photo to the right is an example of complete coverage (thanks Rob).

If you have less than that percentage of coverage you have a couple of options. You can either back-trowel the tile as well as the substrate (back-troweling means combing lines of thinset on the back of the tile as well, not just skimming it with the flat side of the trowel which is called backbuttering), or you can switch to a larger trowel. Both methods will give you more coverage. In the case of back-troweling it will double the amount of thinset beneath your tile.

So those are your coverage requirements and how to check it. Now onto different trowel types…

Types of trowels

types of trowelsTrowels come in a lot of shapes and sizes, even goofy lookin’ ones that look like something out of a Saw movie. The three basic types you should know are the square notch, U-notch and V-notch.

If you look at the horrible graphic I made (my photoshop skills are like a monkey with ten thumbs opening a banana with the keyboard…) you’ll notice that a V-notch will leave the least amount of thinset on your substrate, the U-notch more than that and the square notch will leave the most.

You would be able to visualize this if those horrible graphics were to scale and all the same size. Which they aren’t. Whole monkey-thumbs keyboard-banana thing…

With any mosaic tile you normally want a v-notch, with any large format you normally want a square notch. With average sized tile (12 inches square up to 17” square) you’ll want a u-notch or square notch. With most of my installations I use a square-notch trowel.

Sizing trowels

1/4" X 5/16" V-notch trowelTrowel measurements can be confusing – some have two numbers, some three. So you need to know how to read them.

V-notch trowels normally only have two numbers. The first number is the width of space between the teeth, the second is the depth of the notch.

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1/4 X 1/2 X 3/8 TrowelWith square notch and U-notch trowels  the first number is the width of the teeth, the second is the width of space between those teeth, and the third number is the depth of the space between the teeth. Like this:

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1/4" X 3/8" square notch trowel

If it only has two numbers it means the width of the teeth and the width between the teeth are the same and the second number is the depth of the notch, like the one on the left.

This is the most common sizing you’ll find on a trowel.

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1/4" X 1/4" square notch trowel

If it only has one number, or a trowel is only referred to with one number (as I often do when recommending a trowel) it means that all the measurements are the same. This is what I commonly refer to as a ¼” square notch trowel, even though the graphic says U-notch.

Monkey, thumbs, banana. Yeah.

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SQUARE NOTCH!Here:

Better?

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Which trowel to use

As I stated at the beginning there is no one answer to that. All I can do is tell you what I normally use with what size or type of tile.

1/4" X 1/4" V-notch trowelIf I am installing smaller mosaics (smaller than 2” square) I normally use a ¼” V-notch trowel. This is a ¼” X ¼” trowel.

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1/4" X 1/4" square notch trowelWith mosaics or regular tile larger than 2” square I will use a ¼” square notch trowel ( ¼” X ¼” X ¼”).

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1/4" X 3/8" square notch trowelWith tile 12” x 12” up to 18” x 18” I’ll normally use a ¼” x 3/8” trowel ( ¼” X ¼” X 3/8”)

With tile larger than 18” I’ll either use the ¼” x 3/8” and back-trowel the tile as well, or use a 3/8” X 3/8” or ½” X ½” square or U-notch.

Those are general guidelines and will work with most installations. You NEED to check your coverage with your installation to ensure that you have proper coverage. If you do not have proper coverage you need to back-trowel the tile or use a larger trowel.

The trowel I normally have in my hand is a ¼” X ¼” X 3/8” square notch, I use it for most of my installations (and to irritate random pets…).

This is another one of those questions that, if you ask 50 different contractors, you’re likely to get 50 different answers. For instance the photo of the tile with full coverage at the top is from Rob. It is a 13″ X 13″ tile and he used a 1/2″ x 1/2″ trowel. For most guys it is a personal choice. As long as you get proper coverage there is no wrong answer. The above are simply guidelines and my personal choices. It is up to you to determine whether your trowel is the proper choice for your installation or not.

I can’t see your installation from here. And you know what happens to your dog if you get improper coverage, right?

If you don’t you need to read my blog more.

Just sayin’.

{ 238 comments… add one }

Leave a Comment

  • John

    Hi Roger,
    I took you up on your traditional shower installation manual. Extremely helpful and thorough. I’m ready to begin tiling and have a question. It’s probably somewhere but here goes.
    What size trowel would you recommend for 2″ x 2″ hexagonal marble tile on a mesh backing with 3/32″ grout spacing between each tile? (Tiles are 25/64″ {9.95 mm} thick i.e. a hair over 3/8″ thick)
    And does 1/4″ trowel sound correct for a marble 3″ x 6″ subway tile with 1/16″ grout spacing? (Tiles are 13/32″ {10.33 mm} thick i.e. two hairs over 3/8″ thick)

    Thanks again,

    John

    Reply
  • Gary

    So, after getting my Advantech for my deck amazingly flat, putting on the BARA-RAK, Ditra, and Kerdi seams makes it appallingly not flat/lumpy. This is my first tile project. Should I try to put down the thinset thicker where the kerdi isn’t, use a deeper trowel than the 1/4 x 3/8 I would otherwise use for 13×13 tile, use different trowels for different areas, or some other technique? I’ve tried adult beverages, but my attitude wasn’t sufficiently improved. The BARA RAK edge also slopes off quite a bit, which will likely result in a change of tile slope at the edge unless I counter with extra thinset.

    Reply
    • Roger

      Hi Gary,

      More adult beverages! :D And use a 3/8″ trowel. It will compensate for those unflat areas. Then, more beverages…

      Reply
      • Gary

        I used the 1/4″ x 3/8″ trowel on the deck, and I had my back butter babe trowel on a bit extra with the kerdi (1/8″) trowel after buttering with the flat edge. I knifed off that extra bit wherever the kerdi band was laid. Worked out pretty well. More adult beverages, and a rest for my back, will be required before grouting with Spectralock (and after).

        Reply
  • Erik

    Hey Roger,
    I am getting ready to install Merola metro hex mosaic tile (fxlmhwbd) for my bathroom floor. I also used this in the back of a niche and had a HORRIBLE time work thinset oozing into the grout lines. I was using a1/4″ x 1/4″ square trowel. I bought a 3/16″ x 5/32″ v-notch trowel for the floor but those notches look awful small. Recommendations? Also… any tricks for keeping the thinset out of the grout lines??? Thanks.

    Reply
    • Roger

      Hi Erik,

      Use the 1/4″ trowel and knock the ridges down like you’re installing glass. Once you comb it, use the flat edge of the trowel to smooth out the ridges so you have a flat layer of thinset to lay the tile into. It helps prevent squeeze-through.

      Reply
  • TF

    Hi floor elf, I really found your articles to be informative, but I don’t believe the way you translated each trowel dimension is in the correct order. From other sources I’ve read, the first dimension is the gap with, then gap dad, then gap spacing. My point is out because I was getting confused when reading other websites, and I thought they were wrong, but I think it’s worth investigating if your interpretation is correct.

    Reply
    • Roger

      Thanks TF, I’ll check it. I may have been drunk when I wrote it. :D

      Reply
  • Will Marzolf

    I have techs that will be installing 8″ x 71″ ceramic plank tile 3/8″ thick onto a ceiling. Need to know recommended trowel size to accomplish this. Thank you

    Reply
    • Roger

      Hi Will,

      If you have techs doing it then they should know what size trowel they need – or they shouldn’t be doing it. It is, as stated in the article above, dependent on the particular tile. Not only the size, but how much cupping, what type of substrate on the ceiling, what type of thinset, etc. It is not a magic bullet answer. I would normally use a 1/2″ trowel on tile that large, but that may not work for your particular tile.

      Reply
  • Mark

    Roger,

    Thanks for sharing so much knowledge with your excellent web site.

    With glass mosaics that have random length (3″ to 8″) narrow 3/4″ pieces, would you recommend the v-notch? I want to avoid excessive thinset in the grout lines.

    Also do you have an opinion on euro trowel for 12×12 and larger tile?

    Mark

    Reply
  • Nik

    Hello, I am going to be laying 6×24 porcelain tile for my first tile job. HD recommended Versabond LFT. I bought both 1/2 x 1/2 x 1×2 square trowel and the 1/4 x 3/8 x 1/4 square trowel. The mixing instructions on the bag recommend the larger trowel. In comparing the two, the 1/2 trowel looks like it may be overkill. Will I be okay with using the 1/4 x 3/8 and applying back butter? I’m applying to a level concrete floor.

    Thanks for the help!

    Reply
    • Roger

      Hi Nik,

      Yes, the 3/8 will work just fine.

      Reply