Both square notch and U notch trowels can install tile correctly. The better choice depends on the tile size, mortar, substrate and the coverage you achieve underneath the tile. Square notch trowels are common for ceramic, porcelain and many standard tile installations, while deeper U notch trowels are frequently used with larger tile where more mortar is needed.
The shape of the notch matters because it changes the shape and amount of mortar deposited, but I would not choose a trowel based on notch shape alone.
At BELK Tile, my rule is straightforward: choose the appropriate notch size and shape for the installation, then lift a test tile and verify the mortar coverage.
If you are trying to determine the actual notch size you need, start with our Complete Tile Trowel Size Guide.
Square Notch vs U Notch Trowel: Quick Answer
| Feature | Square Notch | U Notch |
|---|---|---|
| Ridge shape | Square or rectangular | Rounded |
| Common uses | Ceramic, porcelain, subway and many standard tile installations | Large format porcelain and installations requiring a deeper mortar bed |
| Common sizes | 1/4 x 1/4, 1/4 x 3/8 and 1/2 x 1/2 inch | Varies, including deeper large format configurations |
| Mortar ridges | Defined rectangular ridges | Rounded ridges |
| Best choice | Whichever appropriate trowel produces the required mortar coverage for the installation | |
Mike's Tip: Do not get too caught up in whether the notch is square or rounded. The bigger question is whether the trowel is putting down the right amount of mortar and whether those ridges are collapsing underneath the tile.
What Is a Square Notch Trowel?
A square notch trowel has rectangular teeth separated by square or rectangular openings along the edge of the blade.
When you pull the trowel through fresh mortar, those notches create straight, rectangular mortar ridges.
Square notch trowels are among the most common trowels used for tile installation.
Common sizes include:
- 1/4 x 1/4 inch square notch
- 1/4 x 3/8 inch square notch
- 1/2 x 1/2 inch square notch
Different sizes place different amounts of mortar on the substrate, which is why the tile size and installation conditions matter when choosing one.
What Is a U Notch Trowel?
A U notch trowel uses rounded notches rather than square openings.
When mortar is combed with the trowel, it creates rounded ridges.
U notch trowels are commonly associated with larger tile installations because deeper U notch configurations can place a substantial amount of mortar underneath the tile.
One example you will see frequently in large format tile discussions is a 1/4 x 1/2 inch U notch.
What Is the Main Difference Between Square Notch and U Notch Trowels?
The main difference is the geometry of the notch and the resulting mortar ridge.
A square notch produces a ridge with more defined sides and a flatter top. A U notch produces a rounded ridge.
That difference affects how much mortar is deposited and how the ridges behave when the tile is embedded.
However, notch shape is only one part of the equation.
Mortar quantity is also affected by:
- Notch width
- Notch depth
- Spacing between notches
- Trowel angle
- Mortar consistency
- Pressure applied while troweling
That is why comparing a square notch and U notch only by the number printed on the trowel can be misleading.
Does a U Notch Trowel Leave More Thinset?
Not necessarily.
A U notch does not automatically leave more mortar simply because the notch is rounded.
The actual amount of mortar depends on the complete notch dimensions and configuration.
A large U notch can deposit substantially more mortar than a small square notch, but a large square notch can also deposit more mortar than a smaller U notch.
Think about the entire trowel specification rather than comparing only the shape.
Does a Square Notch Trowel Leave More Thinset?
Again, it depends on the dimensions.
A 1/2 x 1/2 inch square notch deposits considerably more mortar than a small square notch, but you cannot conclude that every square notch deposits more mortar than every U notch.
This is one reason manufacturers publish recommended trowel configurations for specific products and applications.
Does a U Notch Collapse Better Than a Square Notch?
You will sometimes hear that rounded U notch ridges collapse more easily than square ridges.
There is some logic behind that idea because the ridge geometry is different, but I would not choose a U notch solely because someone claims it automatically produces better coverage.
Either notch can produce excellent mortar coverage when the trowel is properly sized and the tile is embedded correctly.
The more important technique is to comb straight parallel ridges and move the tile perpendicular to those ridges.
That movement helps the mortar peaks collapse into the valleys and allows trapped air to escape.
When Should You Use a Square Notch Trowel?
Square notch trowels work well for a wide range of ceramic and porcelain tile installations.
Examples include:
- Subway tile
- Medium format ceramic tile
- Porcelain tile
- Bathroom wall tile
- Kitchen backsplash tile
- Floor tile
- Some large format tile installations
A 1/4 x 1/4 inch square notch is one of the most versatile trowels for smaller and medium tile.
A 1/4 x 3/8 inch square notch provides additional mortar for larger tile.
A 1/2 x 1/2 inch square notch is commonly used where significantly more mortar is required, although you should never assume that a larger notch is automatically better.
When Should You Use a U Notch Trowel?
U notch trowels are particularly useful when the installation requires a deeper mortar application.
I commonly consider a U notch when working with:
- 12 x 24 porcelain tile
- Large format porcelain tile
- Porcelain plank tile
- Tile with pronounced patterns on the back
- Installations where a smaller notch does not achieve adequate coverage
A 1/4 x 1/2 inch U notch is a useful starting point for many 12 x 24 porcelain installations.
Square Notch vs U Notch for 12x24 Tile
For 12x24 porcelain tile, I generally like a 1/4 x 1/2 inch U notch, Euro notch or another large format trowel recommended by the mortar manufacturer.
A properly selected square notch can also work.
The important issue is not winning the square versus U notch argument. It is achieving the required mortar coverage underneath a large tile.
With 12x24 tile, I also pay attention to substrate flatness, tile warpage and whether back buttering is needed.
For the back buttering technique, see our Back Buttering Tile Guide.
Square Notch vs U Notch for Subway Tile
For traditional subway tile, a square notch is usually my starting choice.
A 1/4 x 1/4 inch square notch works well for many traditional 3 x 6 ceramic subway tiles.
As the subway tile gets larger, such as 4 x 12 or 4 x 16, a 1/4 x 3/8 inch square notch may be more appropriate.
You generally do not need a deep U notch simply because the tile is being installed on a wall.
Square Notch vs U Notch for Mosaic Tile
For small mosaics, neither a large square notch nor a large U notch is usually desirable.
Small mosaic pieces require enough mortar for proper bonding without so much that mortar pushes through every grout joint.
A small square notch or V notch is generally a better starting point.
For mesh mounted products, our Mesh Mounted Mosaic Tile Installation Guide covers the complete setting process.
Square Notch vs U Notch for Shower Tile
The shower itself does not determine whether the notch should be square or U shaped.
The tile size, tile back and mortar coverage determine the trowel choice.
A small ceramic shower wall tile may work well with a square notch, while a 12x24 porcelain shower wall tile may require a deeper U notch or another large format trowel.
What changes in the shower is the coverage requirement. Wet installations should achieve at least 95 percent mortar contact.
If you are installing large porcelain tile in a shower, see our Porcelain Tile Shower Wall Installation Guide.
Square Notch vs U Notch for Floor Tile
Both square and U notch trowels can be used successfully for floor tile.
A smaller or medium format floor tile may work well with a square notch, while larger porcelain may benefit from a deeper U notch or specialty large format trowel.
The floor needs consistent support beneath the tile, particularly around edges and corners.
Does Tile Size Determine Whether You Need Square or U Notch?
Tile size is an important starting point, but it does not make the decision by itself.
As tile gets larger, you generally need a trowel capable of depositing more mortar.
You also need to consider:
- Tile thickness
- Tile back profile
- Tile warpage
- Substrate flatness
- Mortar type
- Installation environment
This is why I recommend using a trowel chart to get close and a coverage test to make the final decision.
Our Tile Trowel Size Chart provides starting recommendations for the most common tile sizes.
Does the Trowel Angle Matter?
Yes. Trowel angle can significantly change how much mortar is deposited.
Hold the trowel at a consistent angle while combing the mortar.
If you flatten the trowel against the substrate, the ridges become shorter and less mortar is deposited.
If you hold it more upright, the ridges become taller.
That means two installers using identical square notch trowels can still produce different mortar beds.
Should Square and U Notch Mortar Ridges Be Combed Straight?
Yes. Regardless of notch shape, comb the mortar into straight parallel ridges.
Avoid swirls, circles and random patterns.
Straight ridges allow air to escape when the tile is moved perpendicular to them.
The technique is the same whether those ridges started with a square or rounded profile.
Should You Back Butter Tile With a Square or U Notch Trowel?
Traditional back buttering does not normally require combing another set of full mortar ridges onto the back of the tile.
Use the flat side of the trowel to firmly key a thin coat of mortar into the tile back.
The primary mortar ridges are normally combed onto the substrate.
Back buttering is particularly useful with large format porcelain, natural stone and tile with pronounced patterns on the back.
See our complete back buttering guide for more information.
How Do You Know Which Notch Is Actually Working?
Lift a freshly installed tile and look underneath it.
This is the step that settles the square notch versus U notch question for your particular installation.
After setting one of your first tiles:
- Move the tile perpendicular to the mortar ridges.
- Carefully lift it while the mortar is fresh.
- Inspect the mortar transfer on the tile back.
- Look for collapsed ridges.
- Check the center, edges and corners.
- Look for significant continuous voids.
If the coverage is inadequate, make an adjustment before continuing.
How Much Mortar Coverage Should You Have?
As a general benchmark:
- Interior dry installations: At least 80 percent mortar contact.
- Showers and other wet areas: At least 95 percent mortar contact.
- Exterior installations: At least 95 percent mortar contact.
- Natural stone: At least 95 percent mortar contact.
Coverage should also be well distributed without significant unsupported edges, corners or large continuous voids.
Is a Bigger Notch Always Better?
No. Bigger is not automatically better.
An unnecessarily large notch can create:
- Excess mortar squeeze through
- More difficult grout joint cleanup
- Difficulty controlling tile height
- Excessive mortar buildup
- A messier installation
Use the smallest appropriate notch that consistently provides the required mortar coverage.
Can a Trowel Notch Be Too Small?
Yes.
If the notch does not deposit enough mortar, portions of the tile may never make contact.
You may notice large clean areas when you lift a test tile, particularly through the center or around portions of the perimeter.
If proper technique and back buttering still do not produce adequate coverage, you may need a larger or different notch.
Can a Trowel Notch Be Too Large?
Yes.
If mortar constantly squeezes deeply into the grout joints and you already have excellent coverage, the notch may be larger than necessary.
This is particularly common when an oversized trowel is used with thin wall tile or mosaics.
Does the Mortar Manufacturer Matter?
Yes. Always check the setting material manufacturer's recommendations.
Mortars are formulated differently, and manufacturers may specify particular trowel sizes or configurations for certain applications.
The tile manufacturer's installation instructions should also take priority when they specify a particular setting method.
Common Square Notch and U Notch Trowel Mistakes
Choosing by Shape Alone
Square versus U is only part of the decision. Notch dimensions and mortar coverage matter just as much.
Assuming U Notch Is Always Better for Large Tile
A properly sized square, U, Euro or specialty notch may all be capable of producing adequate coverage.
Assuming Square Notch Is Only for Small Tile
Larger square notch trowels are also used for large tile applications.
Using the Same Trowel for Every Tile
The trowel that works for 3 x 6 subway tile is unlikely to be the right choice for a 12 x 24 porcelain floor tile.
Ignoring Trowel Angle
Changing your angle changes the amount of mortar being deposited.
Swirling the Mortar
Comb straight parallel ridges regardless of notch shape.
Never Checking Coverage
No trowel shape or size guarantees proper mortar coverage by itself.
Mike Belk's Rule: Coverage Beats Notch Shape
I would rather see someone use either a square notch or U notch correctly than choose the supposedly perfect trowel and never check underneath the tile.
The trowel is a tool for controlling mortar. The finished mortar coverage is what tells you whether that tool is doing its job.
Choose the appropriate notch for the tile, keep your trowel angle consistent, comb straight ridges, move the tile across those ridges and lift a test tile.
If the coverage is there, you have your answer.
Bottom Line: Square Notch vs U Notch Trowel
Square notch and U notch trowels can both install tile correctly. The best choice is the appropriate notch that deposits enough mortar to achieve proper coverage without creating unnecessary mortar buildup.
Square notch trowels are versatile and work well for many ceramic and porcelain installations. U notch trowels are particularly useful with larger tile and deeper mortar applications.
But the shape stamped into the trowel is not the final answer.
Set a tile, collapse the ridges, pull it back up and check the coverage.
For specific starting sizes for mosaics, subway tile, 12x12, 12x24 and large format tile, visit the BELK Tile Complete Tile Trowel Size Guide.
