Trowel Size Matters: Which trowel size do I use for …?

You want to know which notched trowel to use for your tile project. The boxes of tile that you buy usually don’t tell you which trowel to use with them.

Consequently, I get asked about trowel sizes quite a bit.

Finding the instructions on the trowels or the bags of thinset is a hopeless endeavor. It seems as though it’s a big secret.

So, this post is going to cover:

• Why the trowel have notches in the first place
• Different sizes of notched trowels
• Common tile sizes and which trowels to use (subway, 12×24, etc)

Estimated reading time: 11 minutes

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Why does trowel size matter?

The notches are important on trowels. They leave an even and consistent amount of mortar down to set your tiles into.

Furthermore, the purpose of the notches is to give the mortar a place to “collapse into” once the tile is installed and compressed down.

But here’s the problem:

Asking which tile trowel size to use is the wrong question

I know this seems ridiculous. You’re asking a very simple question and would like a simple answer.

However, because there are so many variations in tile, even in tiles that look similar, it’s not as straightforward of an answer as you would think.

Consequently, what you should be asking is: “Am I getting the proper mortar coverage underneath my tiles?”

It’s all about the coverage

For example, let’s say that you have a ¼ inch x ¼ inch square notched trowel that works great for Home Depot Restore 3×6 subway tile. Additionally, you’ve found this trowel to place the perfect amount of mortar for these tiles.

So, you decide to use this notch trowel again for your new 3×6 extra-thick and wavy handmade tiles from the local specialty store that all the designers rave about. 

But this time you find that there just isn’t enough mortar underneath. It’s not transferring over to the back of the tile. 

Well then, what happened? It’s still the same size tile, isn’t it?

To summarize, this is why it’s important to check your mortar coverage no matter which size trowel someone says to use.

What’s the proper amount of mortar to have underneath my tile?

The proper amount of mortar underneath a tile will allow the tile to be fully supported by the mortar without uncontrollably oozing out of the grout joints. More on this below.

Watch full-length Trowel video on the DIYTileGuy Youtube Channel

For a more exact definition, the American National Standard Specifications for the Installation of Ceramic Tile (ANSI, for short) came up with the following guidelines:

• dry areas need a minimum of 80% coverage
• wet areas (inside a shower, for example) need a minimum of 95% coverage
• Natural stone tiles need a minimum of 95% coverage

Bottom line 

You’ll need to pick the tiles back up from time to time to make sure you’re getting good coverage.

Notched Trowel Size Guide

⅛ inch x ⅛ inch square notch trowel

This is about the smallest notch size trowel that we use in the tile world. Anything smaller is typically for glue applications.

The ⅛ inch square notch trowel is used for some thin waterproof membranes. Which ones? You’ll have to read the instructions for the brand and product that you are installing.

This trowel is also used, occasionally, for very thin glass mosaic tiles with flat backs.

Kerdi Trowel

Schluter Systems has its own branded Kerdi Trowel for installing its Kerdi Shower System. The Kerdi Trowel is simply a ⅛ x ⅛ inch square notch trowel. 

¼ inch x 3/16 inch V-notch trowel

This trowel is used for some thin waterproof membranes. Additionally, certain uncoupling membranes are installed with this size trowel. Again, you’ll need to check what the manufacturer requires for the particular membrane that you are using.

Small mosaic tiles like small, thin hex or penny round tiles are examples that would likely require this trowel size. 

3/16th x 3/16th square notch trowel

This trowel size didn’t use to be common until recently. I use this trowel wherever I would use the ¼ x 3/16 inch V-notch trowel. They apply similar amounts of mortar.

Ditra Trowel

The Ditra Trowel is simply a 3/16 x 3/16 square notch trowel. Technically, they say that it’s 5/64 x 5/64. This trowel size is what you would use to install the ⅛ inch thick Ditra Membrane.

¼ inch x ¼ inch square notch trowel

This is, quite likely, the most common size of trowel that tile setters own. We use this trowel size for:

• Cement board
• Certain uncoupling membranes
• Some of the thicker uncoupling membranes like the uncoupling heat membranes
• Some mosaic tiles typically in the 2-3 inch range
• Certain glass mosaic tiles such as the mixed linear glass mosaic tiles that you see in the video
• Subway tile and other ceramic tiles up to 6×6 inches square
• Pebble tile
• As well as other applications

Ditra-Heat Trowel

The Ditra-Heat Trowel is a ¼ inch x ¼ inch square notch trowel. You would use this size with Ditra-Heat, Ditra-Heat Duo, and Ditra XL.

¼ inch x ⅜ inch square notch trowel

This trowel would be used for some of the thicker uncoupling heat membranes (check with the manufacturer).

This sized notch trowel is also great for installing 12x12s, 13×13’s, and 16×16’s.

Additionally, I like to use this size trowel for the bigger “subway” tiles such as the 4×12’s and 4×16’s. 

½ inch x ½ inch square notch trowel

The big ½ inch square notch trowel is used for big tiles. You want to use this for most tiles that are 16-inches and larger. So, this is a good trowel size for 12×24’s, 16×16’s, 6×24’s, 8×36’s, wood-look plank tiles, etc.

Additionally, it’s a good choice for natural stone tiles 12×12 and larger like marble, granite, and travertine.

Specialty trowels

Euro Notch trowel

The Euro notched trowel is an innovation that is designed to collapse the ridges in the mortar in a more efficient way.

This type of trowel will often be specified when installing the really large thin porcelain tile panels that are becoming more popular today.

Slant notched trowel

Slant notched trowels are also designed to collapse the ridges in the mortar more easily. These trowels are a little harder to come by, though.

Margin Trowel

The margin trowel has nothing to do with combing mortar. Rather, it’s a tool that every tile setter owns and uses in a variety of ways.

It really is an essential tool from scooping mortar out of the bucket, lifting tiles, and cleaning the mortar from around the edge of the tile.

Margin trowels come in two different sizes but the 5-6 inch is the most popular.

Best Practices when Troweling mortar

Yes, there are even best practices when troweling mortar on a wall or floor. Please keep in mind these are not rules but simply recommendations.

The bottom line is always to get the required amount of mortar coverage on the back of the tile. These two tips will help you achieve this goal.

Directional Troweling

When troweling thinset mortar, the best way to do it is to comb the notches in one direction. You then install the tile and wiggle it back and forth against the notches. This is the best way of collapsing the ridges into one another.

Additionally, when installing a rectangular, or oblong tile, you want to comb the notches so that they are perpendicular to the long direction of the tile. The reason being that this is the shortest path for air to escape.

Back Buttering Tile

Back buttering is another practice that helps you achieve maximum mortar coverage on your tile. What the heck is back buttering?

It’s when you “key in” the mortar to the back of the tile. In other words, you’ve spread the mortar notches in one direction on the floor or wall, you then spread mortar on the back of the tile using the flat side of your notch trowel and scrape it off. 

What this does is:

• Force the mortar into the back of the tile
• Fills in the uneven backing so that it’s a flat surface

Back buttering should be done on any tile that is 12×12 and larger, in my opinion.

Doing these two things, directional troweling and back buttering your tile, will help you to achieve the minimum amount of mortar required for your project.

FAQ about tile notch trowels

What size trowel for subway tile?

Typically, a ¼ inch x ¼ inch square notch trowel is perfect for the average subway tile

What size trowel for 12×24 inch tile?

A ½ inch x ½ inch square notch trowel or a ¼ inch x ½ inch square notch is a good size for this tile.

Don’t forget to trowel your notches the short way and back butter the tile

What size trowel for mosaic tile?

A ¼ inch x ¼ inch square notch trowel is typically the right choice for 2×2 and 3×3 mosaic tiles that come in sheets.

What size trowel for 6×24 tile?

A ½ x ½ inch square notch trowel is my preferred trowel for this size tile. You could also use a ¼ inch x ⅜ inch square notch trowel. 

Make sure to fill the hump in the center of the tile with mortar.

What size trowel for 6×36 tile?

A ½ x ½ inch square notch trowel is a good choice for this size of tile.

What size trowel for 12×12 wall tile?

A ¼ inch x ⅜ inch square notch trowel works well for most 12 x 12 tiles (30cm x 30cm).

What size trowel for penny tile floor?

¼ inch x 3/16 inch V-notch trowel works well for most penny-round tiles. A 3/16 inch x 3/16 inch square notch trowel (Ditra trowel) works just as well.

Square notch vs U notch tile trowels

This is when the end of the channel on a notched trowel is rounded instead of square.

It’s my understanding that the U-notch is supposed to perform better but I don’t know the reason why. I think the idea is that is would compress into the back of the tile in a better way. 

In my opinion, there really isn’t a compelling reason to choose a U-notch over its similar-sized square notch counterpart. It will spread slightly less mortar than the square notch as the measurement is taken at the top of the arch.

How much mortar is left under the tile once it’s compressed?

Let me start by saying that this isn’t a straightforward calculation. It’s usually the engineers that are trying to precisely determine how thick the whole tile assembly is going to be.

Take a ¼ x ¼ inch square notch trowel, for example. One might think that since the notch is ¼ inch tall and ¼ inch wide that compressing the tile simply fills in the space. Therefore, half of the ¼ inch high notch fills in the space leaving it ⅛ inch high.

I’ve even seen another blog use this very calculation but it isn’t correct. They don’t factor in that you are holding the trowel at an angle and not straight up & down. Therefore the mortar that is combed onto the floor isn’t ¼ inch high.

So in the case of the ¼ x ¼ inch square notched trowel, the actual amount of mortar might be closer to 3/32. 

But, again, the variables are the angle of the trowel, the consistency of the mortar, how well the notches are collapsed, and whether the tile was back buttered, or not.

What’s reassuring is that even if your calculations are slightly off you can still make small adjustments to make up for variations.