Using the proper trowel

by Roger

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.


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:


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.


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.





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.


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”).


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’.

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Roger I’m going to use three different tile sizes on the shower walls 6×6, 2×2 mosaic, and 18×18 based on guides they all take different trowel sizes, wont the different trowel sizes have different amounts of thinset and make the tiles different thicknesses?

The mosaics already seem a little thinner than the other two sizes and I’m afraid of making it worse. I was thinking using more thinset would just make a mess on the mosaics. The difference doesn’t seem to be enough to use your Detra trick any other suggestions?



Hi Gem,

You can use the same trowel for all of them. When installing the mosaics just spread your thinset with the ridged side of the trowel, then flip it over and knock down the ridges flat so you have a flat bed of thinset to lay them into. Lay the thicker tiles with just thinset on the wall, the slightly thinner ones with thinset on the wall and the back of the tile.



HI Rodger, great suggestions. How do I determine the final thickness of the thinset based on the trowel? 1/4 x 1/4 = 1/8 seems to make sense. What would I have with 1/4 x 3/8 for instance?




Hi Gary,

That trowel will leave approx 1/4″ of thinset bed. It is not exact, and you’ll never get an exact amount. But it can be tweaked as you’re setting the tile.



Not a brilliant retort, but a heartfelt question….
Hardibacker instructions say to fill joints with mortar and embed blah blah blah tape. If my intention is to use Hydroban, could I tape joints and Hydroban over everything and skip filling the joints with mortar? Is this tape we speak of self-adhesive?



Hi Bonnie,

No, you still need to tape and mud the joints, let it cure, then hydroban everything. It is adhesive enough to stick up there before you get the thinset over it.



Backer board screws don’t bottom out if your drill has the proper torque needed. Try flipping the switch on top of your drill to the #1 setting (as opposed to the #2 where it currently is). Of course this implies the use of at least an 18v cordless drill. If you are trying to use a cordless screwdriver, that’s never going to work.

Also, if the screw starts to strip out at the end, change the setting to #1, and don’t try and push so hard, or go so fast. Slow and easy will totally make the process that much more fun. Actually, it won’t suck as much.

I have personally never had to score both sides of 1/2″ Hardiebacker, but I can see how doing that would give you a perceived easier cut. I would bet that if you counted the number of scores you do on the front and back added together, then scored one side with that combined total, the results would be very similar. Unfortunately scoring and snapping 1/2″ is not always the quickest and easiest process.

Hopefully Roger will not blast me for chiming in with my two cents, but wanted to at least offer some help in Roger’s absence.



What you are saying is possible by stripping the thread made by the screw. If you don’t drill a hole you think think board is down when the screw bottoms out unless, you have a powerful driver most people don’t. It is no problem to pre drill a hole and you know the board is down when the screw bottoms out, I feel it is a safer way especially for the one timer.
Because the backer it is two boards glued together the unscored board does not know where to snap. You can use a saw, but it is messy to do inside a house, with the dust it makes, which is also hazardous. I have to remodel while I am living in the house and winter means things have to be done inside.


john cory

Is there any bonding product on the market you put on tiles to aid the hold



Hi John,

I don’t really understand the question. The bonding strength of any particular thinset is more that adequate to achieve a proper bond, why would you want or need anything more?



I’m going to be putting in a new stone floor. I’m removing nearly 3000 sq ft of Saltillo or terra cotta floor tiles with lipage so bad that I’ve actually stubbed my toes on the tile edges several times :censored: Not to mention the approximately 1″ grout lines that, while they follow a fairly straight line from one end of the house to the other, the variation of where the tile was placed makes the grout line kind of thicker and thinner in places so it kind of…wanders. I have exceptionally long hallways so this is a real eyesore for me so I want to get rid of the long (hopefully) straight grout lines with the new floor I’m putting down.

I’m going to be putting down Chisled edge travertine in an antique pattern. I’m sure your familiar. The stone is half an inch thick and individual tiles range in size from 6×6,6×18,18×18, etc… I have a small area, about 200 sq’ in my master bedroom that I’m starting with that doesn’t connect to any other section of tile floor in the house. I’m starting there so I can get comfortable with this product and pattern. Oh… It’s going down on a concrete slab… Probably important to mention that… The manufacturer said that the tile could be installed with or without grout lines (it is rectified). I thought about that for a second and it doesn’t make much sense. If using a 1/8 grout line, there will be 3 or 4 tiles from one end of the pattern to the other in some places and only 1 or 2 in others. This means that the pattern grows by as much as 1/2 inch in places and only 1/8 in others. Wouldn’t this throw the whole damn thing off? :wtf:

This leads to my list of several questions.
1. Am I correct about my assumption that uniform sized grout lines aren’t possible with this product, or am I just a moron? :bonk:
2. If I install the tiles without a grout line, should I grout the seams anyway to take up any gaps and imperfections in the edges?
3. How should I go about laying these stone tiles and avoid the aweful lipage?

This isn’t my first tile job, I’ve put down 4 bathrooms 2 showers and an entryway in the last few years, but always with porcelain or ceramic squares with grout lines, never natural stone and never with such an intricate pattern. I’m trying to make this house have a high end look and feel, so a poorly installed expensive stone floor just won’t do. Any advice you have on installing the different sized tiles properly would be greatly appreciated.

Thanks in advance.



Hi Sean,

1. You are correct.
2. DO NOT lay the tile without grout lines, especially in an installation that size. They’ll be more chiseled edge every time one cracks. :D
3. You can use varying 1/16″ and 1/8″ or 1/8″ and 3/16″ grout lines on that pattern. Smaller tile gets the larger grout line. Flat floor tile.


Sean Geery

I want to install a mosaic floor tile that has 144 1″ hexagon tiles on a mesh backing on the kitchen floor. Ii is in an old row house from the late 1800’s hence the “old” style tile. I am installing 1/4″ hardi and some electric radiant Laticrete floor heat in the open area. To minimize thin set squeezing up would I install the kerdi, waffle side down (no waterproofing here – just uncoupling feature) with modified thin set and large notched trowel and then use modified and a small v-notch to lay the mosaic?




Hi Sean,

You can’t install anything smaller than 2″ tile on ditra. It won’t have the proper support. I would use 1/2″ hardi and install directly to that.



You answered my question. AND I laughed. Hard.



I have some hand made cement tiles by Marrakesh Design 8″x8″ and 1/2″ thick. Need to lay them on plywood and to match edge of 3/4″ hardwood floor. Specs ask for thin-set mortar and a notched trowel. What kind of thin-set mortar (with polymer/without) should I use and size of trowel please?



Hi Maria,

Modified mortar. And you need a proper substrate beneath your tile – bare plywood is not it. Trowel size will be dictated by how much build-up you need between your proper substrate and the hardwood, minus the depth of the tile.



Hi Roger, I’m planning my first bathroom renovation. So, in picking out the tiles I noticed that the the two tiles I plan on using vary in thickness. We found medium sized subway tiles, set on a 12″x 12″ x 6mm mesh, and the accent tiles are tiny mother-of-pearl mosaic, set on a 12″ x 12″ x 8mm mesh. Would I need different trowels for both tiles to assure that they are level? Thanks in advance!



Hi Gabi,

There are several ways to do it, different trowels is one, or this.


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