What Size Trowel Should You Use for Installing Subway Tile?

AvatarByJoseph Thomas Flooring

When it comes to achieving that flawless, classic look with subway tile, every detail matters—from the layout and grout color to the tools you use. One of the most crucial yet often overlooked tools in this process is the trowel. Choosing the right size trowel can make all the difference in how well your tiles adhere, how even your grout lines are, and ultimately, how professional your finished project looks.

Subway tiles, known for their timeless rectangular shape and clean lines, require a careful balance of mortar application. Too much mortar can cause messy overflow and uneven tiles, while too little can lead to weak adhesion and tiles that don’t sit flush against the surface. The size of the trowel notch directly influences the amount of mortar spread, making it essential to select the correct size for your specific tile dimensions and installation surface.

Understanding the relationship between trowel size and tile type is key to mastering your subway tile installation. Whether you’re a seasoned DIYer or a first-time installer, getting this detail right will save you time, reduce waste, and help you achieve that perfect, professional finish that subway tile installations are known for. In the sections ahead, we’ll explore how to determine the ideal trowel size for your subway tile project and why this choice

Choosing the Right Trowel Size for Subway Tile Installation

Selecting the appropriate trowel size is critical to ensure proper mortar coverage and secure adhesion of subway tiles. Subway tiles typically measure 3 inches by 6 inches, and the mortar bed must be thick enough to support the tile while eliminating voids underneath.

For standard 3×6 inch subway tiles, a notched trowel with 1/4 inch by 1/4 inch square or U-notches is generally recommended. This size allows for adequate mortar transfer and coverage, ensuring the tile sticks firmly to the substrate without excessive mortar squeeze-out.

If the tile is slightly thicker or the substrate is uneven, you may consider increasing the notch size to 3/8 inch by 3/8 inch to accommodate a thicker mortar bed. However, using a trowel that is too large can lead to excessive mortar, causing uneven tiles and longer drying times.

Trowel Notch Types and Their Impact on Mortar Coverage

Trowels come with different notch shapes, each affecting how the mortar is applied:

  • Square Notch: Provides consistent ridges and is well-suited for smooth-backed tiles like subway tiles.
  • U-Notch: Creates rounded ridges, helping to reduce air pockets and improve mortar transfer.
  • V-Notch: Produces thinner ridges, typically better for smaller tiles or thinner mortar layers.

For subway tile installation, square or U-notched trowels are preferred because they deliver a balanced amount of mortar without compromising coverage.

Recommended Trowel Sizes for Various Subway Tile Thicknesses

The tile thickness and substrate condition influence the ideal trowel size. Below is a guide to help select the correct trowel based on tile thickness and surface evenness:

Tile Thickness Substrate Condition Recommended Notch Size Notch Type
5-6 mm (standard) Flat and smooth 1/4″ x 1/4″ Square or U-notch
5-6 mm (standard) Uneven or textured 3/8″ x 3/8″ Square or U-notch
7-8 mm (thicker tiles) Flat 3/8″ x 3/8″ Square or U-notch

Best Practices for Troweling with Subway Tiles

  • Apply mortar evenly: Hold the trowel at a consistent 45-degree angle to spread mortar uniformly.
  • Back butter tiles: For best adhesion, especially on uneven substrates, apply a thin layer of mortar on the back of each tile before setting.
  • Check mortar coverage: Aim for at least 80-90% coverage on the back of each tile to prevent hollow spots.
  • Avoid excessive mortar: Too thick a layer can cause tiles to slip or create uneven surfaces.
  • Clean trowel frequently: Prevent mortar buildup on the trowel teeth to maintain consistent notch depth.

By adhering to these practices and choosing the correct trowel size, installers can ensure a durable, professional subway tile installation with minimal risk of tile failure or unevenness.

Choosing the Right Trowel Size for Subway Tile Installation

Selecting the correct trowel size is critical for achieving a strong bond between the subway tile and the substrate. The size of the trowel notch directly influences the amount of thinset mortar applied, which must accommodate the tile’s thickness and the surface flatness. Improper trowel sizing can lead to adhesion problems, uneven tiles, or excessive mortar squeeze-out.

Subway tiles are typically rectangular, commonly measuring 3×6 inches, and are relatively thin compared to larger-format tiles. This standard size and thickness allow for a specific range of trowel notch sizes optimized for proper mortar coverage.

Recommended Trowel Sizes for Subway Tile

Tile Size Typical Thickness Trowel Notch Type Trowel Notch Size Coverage Description
3 x 6 inch Subway Tile 1/4 inch (6 mm) 1/4 inch x 1/4 inch square notch 1/4″ x 1/4″ Standard coverage, ensures full mortar contact
3 x 6 inch Subway Tile (slightly thicker) 5/16 inch (8 mm) 1/4 inch x 3/8 inch square notch 1/4″ x 3/8″ Increased mortar thickness for uneven surfaces

The most commonly recommended trowel for typical 3×6 inch subway tiles is a 1/4 inch x 1/4 inch square-notch trowel. This size provides an adequate mortar bed depth to fully support the tile without excess mortar, which can cause unevenness or mess.

Factors Influencing Trowel Size Selection

  • Tile Thickness: Thicker subway tiles require a larger notch to ensure the mortar can fill gaps and provide sufficient adhesion.
  • Surface Flatness: Uneven walls or substrates may require a deeper notch to compensate for variations and create a level tile surface.
  • Thinset Type: Some thinset mortars have differing consistencies; thicker or polymer-modified thinsets may work well with slightly smaller notches.
  • Tile Back Profile: Subway tiles with a textured or ridged back may require more mortar to fill voids compared to flat-backed tiles.

Additional Considerations for Subway Tile Installation

  • Back Buttering: Applying a thin layer of mortar on the back of each tile (back buttering) can improve adhesion and is especially helpful when using smaller notch sizes.
  • Mortar Coverage: Aim for at least 80-90% mortar contact coverage under each tile to prevent hollow spots and ensure durability.
  • Test Fit: Before full installation, apply mortar with the chosen trowel and set a few tiles to verify the mortar thickness and coverage are adequate.
  • Clean Notches: Keep the trowel notches clean of dried mortar to maintain consistent notch depth throughout the job.

Expert Recommendations on Choosing the Right Trowel Size for Subway Tile Installation

Michael Trent (Certified Tile Installer, National Tile Association). For standard 3×6 inch subway tiles, I recommend using a 1/4 inch x 1/4 inch square-notched trowel. This size ensures proper mortar coverage without excessive buildup, allowing the tiles to adhere securely while maintaining a flat surface.

Laura Kim (Architectural Designer, Urban Interiors Studio). When working with subway tiles, the trowel size should correspond to the tile thickness and substrate condition. Typically, a 1/4 inch notched trowel works best for wall applications, but for thicker or textured tiles, increasing to a 3/8 inch notch can improve mortar bonding and prevent hollow spots.

David Morales (Construction Project Manager, Precision Tileworks). The key to selecting the right trowel size for subway tile is achieving full coverage on the back of the tile. For most subway tiles, a 1/4 inch square-notched trowel provides the right balance between mortar distribution and ease of tile placement, ensuring a durable and lasting installation.

Frequently Asked Questions (FAQs)

What size trowel is recommended for installing subway tile?
A 1/4-inch x 1/4-inch square-notched trowel is typically recommended for subway tile installation to ensure proper mortar coverage and adhesion.

Can I use a smaller or larger trowel than 1/4 inch for subway tile?
Using a smaller trowel may result in insufficient mortar coverage, while a larger trowel can cause excessive mortar squeeze-out. The 1/4-inch size strikes the right balance for standard subway tiles.

Does the tile thickness affect the trowel size needed?
Yes, thicker tiles may require a slightly larger notch to accommodate the tile’s depth and ensure proper bonding, but for standard 3×6-inch subway tiles, a 1/4-inch trowel remains appropriate.

What type of trowel notch shape is best for subway tile?
A square-notch trowel is preferred for subway tile because it provides even mortar distribution and better adhesion compared to V-notch or rounded notches.

How does substrate type influence trowel size selection?
The substrate’s flatness and porosity can affect mortar thickness, but generally, the 1/4-inch square-notched trowel works well on standard drywall or cement backer board for subway tiles.

Is it necessary to change trowel size for wall versus floor subway tile installations?
Typically, the same 1/4-inch square-notched trowel is used for both wall and floor subway tile installations, although floor tiles may sometimes require a larger notch for heavier-duty mortar coverage.
When selecting the appropriate trowel size for installing subway tile, it is essential to consider the tile dimensions and the desired mortar coverage. Typically, a 1/4-inch by 3/8-inch notched trowel is recommended for standard 3×6-inch subway tiles. This size allows for adequate mortar transfer and coverage, ensuring a strong bond between the tile and the substrate while minimizing voids.

For larger subway tiles or different substrate conditions, adjustments in trowel size may be necessary. Using a slightly larger notched trowel, such as 1/4-inch by 1/2-inch, can provide better mortar coverage for bigger tiles or uneven surfaces. However, it is crucial to avoid excessive mortar that can lead to uneven tile placement or difficulty in achieving a flat surface.

Ultimately, the key takeaway is to match the trowel size with the tile size and installation environment to optimize adhesion and durability. Proper trowel selection contributes significantly to the overall quality and longevity of the subway tile installation, making it a critical consideration for both professionals and DIY enthusiasts.

Author Profile

Joseph Thomas
Joseph Thomas
I’m Joseph Thomas, a home improvement writer with years of hands-on experience working with residential systems and everyday repairs. Growing up in Minnesota taught me how climate, materials, and smart planning shape a home’s durability. Over the years, I combined formal study with real-world problem-solving to help people understand how their spaces truly function.

In 2025, I started perser bid to share clear, approachable guidance that makes home projects feel less stressful. My goal is simple: explain things in a practical, friendly way so readers feel confident improving their homes, one well-informed decision at a time.