For most 12x24 tile installations, I recommend starting with a 1/4 x 1/2 inch U notch trowel, Euro notch or another large format tile trowel recommended by the mortar manufacturer. A 1/2 x 1/2 inch square notch is also commonly used, but the number stamped on the trowel is not what ultimately determines whether it is correct.
The real test is mortar coverage.
After setting your first tile, pull it back up and inspect the mortar transfer. For a typical dry interior installation, you want at least 80 percent mortar contact. In showers, other wet areas and exterior installations, you should achieve at least 95 percent coverage.
If you are not getting the required coverage, adjust your trowel, back buttering or setting technique before continuing.
If you need recommendations for other tile dimensions, see our complete tile trowel size guide.
Quick Answer: Best Trowel Size for 12x24 Tile
| 12x24 Tile Application | Starting Trowel | Mortar Coverage Goal |
|---|---|---|
| Interior dry floor | 1/4 x 1/2 inch U notch or large format notch | At least 80% |
| Interior dry wall | 1/4 x 1/2 inch U notch or manufacturer recommended notch | At least 80% |
| Shower wall | 1/4 x 1/2 inch U notch or large format notch | At least 95% |
| Bathroom floor outside shower | 1/4 x 1/2 inch U notch or large format notch | At least 80% |
| Exterior installation | Manufacturer recommended large format notch | At least 95% |
Mike's Tip: Think of the trowel size as your starting point, not your final answer. Set a 12x24 tile, move it across the mortar ridges and pull it back up. The mortar coverage underneath the tile tells you whether your trowel and technique are working.
Why Does 12x24 Tile Need a Larger Trowel?
A 12x24 tile is considered a large format tile because one side is longer than 15 inches. As tile gets larger, achieving consistent mortar contact across the entire back becomes more challenging.
A small tile can follow minor variations in a wall or floor relatively easily. A 24 inch long porcelain tile cannot.
Several conditions can create areas where the back of a 12x24 tile does not contact the mortar:
- Minor low spots in the substrate
- Ridges or patterns on the back of the tile
- Slight tile warpage or bowing
- Improper troweling technique
- Mortar that begins to skin over before the tile is set
- Failure to properly embed the tile into the mortar
A deeper notch places enough mortar on the substrate to help establish the required contact when the tile is properly embedded.
However, a larger trowel should never be used to compensate for a badly uneven floor or wall. Substrate preparation comes first.
Is a 1/4 x 1/2 Inch U Notch Good for 12x24 Tile?
Yes. A 1/4 x 1/2 inch U notch is one of my preferred starting trowels for 12x24 porcelain tile.
The deeper notch deposits substantially more mortar than a standard 1/4 x 1/4 inch square notch while the rounded U shaped ridges can collapse effectively when the tile is moved across them.
That makes it a useful choice for large rectangular tile.
It is still necessary to check coverage. Tile back geometry, substrate conditions and mortar characteristics can change the amount of mortar required.
Can I Use a 1/2 x 1/2 Inch Trowel for 12x24 Tile?
A 1/2 x 1/2 inch square notch is commonly used for 12x24 tile and can provide enough mortar for many installations.
That does not mean it is automatically the best choice for every 12x24 tile.
I prefer to think in terms of coverage rather than trying to declare one notch universally correct.
If a 1/2 inch square notch gives you the required mortar contact, proper finished mortar thickness and manageable squeeze through, it can be an appropriate choice.
If another large format notch achieves the same or better coverage more efficiently, use that instead.
Can You Use a 1/4 x 1/4 Trowel for 12x24 Tile?
I would not choose a 1/4 x 1/4 inch square notch as my normal starting trowel for a 12x24 tile.
That size works well for many smaller ceramic and porcelain tiles, but a 12x24 tile has a much larger surface area and commonly needs more mortar to achieve consistent contact.
The question is not whether you can physically install the tile using a smaller notch. The question is whether that notch produces the required mortar coverage beneath your particular tile.
If it does not, the installation is under supported regardless of how flat the finished tile looks.
U Notch vs Square Notch for 12x24 Tile
Both U notch and square notch trowels can be used successfully for large format tile, but they create different mortar ridge profiles.
1/4 x 1/2 Inch U Notch
A U notch creates rounded mortar ridges and is an excellent starting choice for many 12x24 installations. I like it because it deposits a useful amount of mortar while allowing the ridges to collapse as the tile is embedded.
1/2 x 1/2 Inch Square Notch
A 1/2 x 1/2 inch square notch places a substantial amount of mortar and is commonly recommended for large format tile. It can work well when the substrate, tile and mortar are appropriate for it.
Euro and Specialty Notch Trowels
Euro, slant and other specialty large format trowels are designed to create mortar ridges that collapse efficiently during installation.
They can be excellent choices for 12x24 porcelain tile, particularly when recommended by the mortar manufacturer.
Rather than choosing based on notch shape alone, I would select a suitable large format trowel and then verify what is happening underneath the tile.
What Size Trowel for 12x24 Floor Tile?
For 12x24 floor tile, start with a 1/4 x 1/2 inch U notch, Euro notch or another large format tile trowel that provides sufficient mortar for the installation.
Floor tile needs consistent support because unsupported voids can become weak points under foot traffic, furniture and concentrated loads.
Before setting tile, make sure the floor is sufficiently flat for large format tile. A deep trowel should not become a substitute for substrate preparation.
After installing your first tile, remove it and inspect the mortar transfer.
For a dry interior floor, achieve at least 80 percent mortar contact, with good support around tile edges and corners.
What Size Trowel for 12x24 Wall Tile?
A 1/4 x 1/2 inch U notch or another manufacturer approved large format notch is a good starting point for most 12x24 wall tile.
Do not automatically switch to a smaller notch simply because the tile is going on a wall.
The same 12x24 tile still has to achieve adequate mortar contact.
Large wall tile also introduces another consideration: mortar sag resistance. Use a setting material approved for large format tile and appropriate for vertical installations.
What Size Trowel for 12x24 Shower Wall Tile?
For a 12x24 porcelain shower wall, a 1/4 x 1/2 inch U notch or appropriate large format trowel is a strong starting point, but the installation needs at least 95 percent mortar coverage.
That higher coverage requirement is especially important in a wet environment.
I recommend back buttering the tile, combing the mortar in one direction and checking coverage early in the installation.
Do not assume that because the tile feels firmly attached to the wall that the coverage underneath it is adequate.
For the complete installation process, read our guide to installing porcelain tile on shower walls.
Should You Back Butter 12x24 Tile?
Yes, I recommend back buttering most 12x24 porcelain tile installations.
Back buttering means using the flat side of your trowel to firmly key a thin layer of mortar into the back of the tile.
You are not trying to create another thick bed of mortar.
The objective is to fill the texture and depressions on the tile back and improve contact between the tile and the mortar that has been combed onto the substrate.
Back buttering is particularly useful when:
- Installing large format porcelain
- Working in a shower or wet area
- The tile has deep patterns on the back
- The tile has minor warpage
- Very high mortar coverage is required
For a deeper explanation, see our complete guide to back buttering tile.
How Should You Trowel Mortar for 12x24 Tile?
Trowel technique is just as important as trowel size.
Comb the mortar into straight, parallel ridges rather than creating swirls or random patterns.
With a rectangular 12x24 tile, I prefer the ridges to run parallel to the short dimension of the tile. This gives trapped air a shorter path to escape.
After placing the tile into the fresh mortar, move it perpendicular to the direction of the ridges.
This movement helps collapse the mortar ridges into the valleys between them, creating a more continuous mortar layer underneath the tile.
How to Set 12x24 Tile for Proper Mortar Coverage
- Prepare the substrate. Make sure the floor or wall is clean, sound and sufficiently flat for large format tile.
- Mix the mortar correctly. Follow the manufacturer's water ratio, mixing and slake instructions.
- Key mortar into the substrate. Use the flat side of the trowel and firmly press mortar against the surface.
- Comb straight mortar ridges. Hold the trowel consistently and run the ridges in one direction.
- Back butter the tile. Key a thin layer of mortar into the back of the 12x24 tile.
- Set the tile while the mortar is fresh. Do not allow the surface of the mortar to skin over.
- Move the tile across the ridges. Move it perpendicular to the ridge direction to help collapse them.
- Lift a test tile. Check the actual mortar transfer before continuing.
How Much Mortar Coverage Does 12x24 Tile Need?
A 12x24 tile installed in a typical dry interior application should have at least 80 percent mortar contact. Wet and exterior installations require at least 95 percent coverage.
Coverage should also be distributed properly.
You do not want one large unsupported void in the center of the tile even if enough mortar exists elsewhere to make the overall percentage appear acceptable.
Edges and corners need good support as well.
How Do You Check Mortar Coverage on 12x24 Tile?
The simplest method is the lift and check test.
Set the tile exactly as you normally would. Move it perpendicular to the mortar ridges and then carefully lift it back off the substrate.
Look at the back of the tile.
You want to see that the mortar ridges have collapsed and transferred across the tile rather than remaining as distinct untouched lines with large empty spaces between them.
If coverage is insufficient, do not simply continue installing tile.
Determine why.
You may need to:
- Use a different trowel size
- Adjust the angle of the trowel
- Improve your directional troweling
- Back butter the tile
- Correct substrate flatness
- Replace mortar that has begun to skin over
Does 12x24 Porcelain Tile Need Large Format Mortar?
Use a mortar that the manufacturer approves for the tile size, substrate and application you are installing.
Many mortars are specifically formulated for large and heavy tile. These products are designed to support larger tile while maintaining the appropriate mortar bed.
Do not choose mortar based only on the word "thinset." Check the product's technical data and confirm that it is approved for your 12x24 tile and installation surface.
Does the Substrate Need to Be Flat for 12x24 Tile?
Yes. Substrate flatness becomes increasingly important as tile gets larger.
A 12x24 tile cannot bend to follow dips and humps in a floor or wall. Trying to compensate for significant substrate irregularities with extra mortar makes the installation harder to control and can contribute to lippage and inconsistent coverage.
Check the substrate with an appropriate straightedge before installation and correct significant irregularities before you begin setting tile.
Common 12x24 Tile Trowel Mistakes
Automatically Using a 1/4 x 1/4 Inch Trowel
A 1/4 x 1/4 inch trowel is useful for many smaller tiles, but I would not make it my default choice for a 12x24 tile.
Assuming 1/2 Inch Is Always Correct
A larger notch is only correct if it produces the required coverage for your particular tile and installation.
Skipping the Coverage Test
This is probably the easiest mistake to prevent. Lift one of your first tiles and look underneath it.
Swirling the Mortar
Swirls can trap air. Straight, parallel ridges give air a path to escape as the tile is embedded.
Skipping Back Buttering
Back buttering can make a substantial difference in mortar transfer with large porcelain tile.
Trying to Fix an Uneven Floor With a Bigger Trowel
Correct significant substrate problems before installation rather than attempting to compensate with an excessively thick mortar bed.
Letting Mortar Skin Over
If you spread too much mortar at once, its surface can begin drying before the tile is installed. That reduces mortar transfer even when you are using the correct trowel.
Bottom Line: What Trowel Should You Use for 12x24 Tile?
For 12x24 tile, I would start with a 1/4 x 1/2 inch U notch, Euro notch or another appropriate large format trowel. A 1/2 x 1/2 inch square notch is another commonly used option.
But I would never choose the trowel based on tile dimensions alone.
Prepare a flat substrate, use mortar approved for large format tile, key the mortar into the substrate, comb straight ridges, back butter the tile when appropriate and move the tile perpendicular to those ridges.
Then pull up one of your first tiles and inspect it.
For dry interior applications, achieve at least 80 percent mortar coverage. For showers, other wet areas and exterior installations, achieve at least 95 percent.
That coverage check is what tells you whether you have the right trowel.
For recommendations covering mosaics, subway tile, 12x12 tile, shower floors, glass tile and other formats, visit the BELK Tile Complete Tile Trowel Size Guide.
