Understanding Thinset Coverage
Thinset coverage is not a precise geometric calculation but a manufacturer-supplied estimate based on the **trowel notch size**. The notches create ridges, and when the tile is pressed down, these ridges collapse to form the final bond coat.
Trowel Notch Selection Guide
Common Trowel Notches and Use
- **1/4" x 1/4" Square:** Good for small tiles (e.g., 6" x 6") and mosaics.
- **3/8" x 3/8" Square:** The most common trowel for standard-sized floor tiles (e.g., 12" x 12" or 16" x 16").
- **1/2" x 1/2" Square or U-notch:** Required for large format tiles (LVT) that are 18" or longer on any side, ensuring proper coverage and support.
- **Back Buttering:** For LVT or stone, always apply a thin layer of thinset directly to the back of the tile in addition to the floor/wall.
Factors Affecting Actual Yield
- **Substrate Roughness:** A rough concrete floor will require more thinset than a smooth cement board.
- **Tile Flatness:** Curved or warped tiles require more thinset to achieve a flat surface.
- **Mix Consistency:** A slightly runnier mix will spread further but may compromise bond strength (use water quantity exactly as directed).
- **Lippage:** Using a larger-than-necessary trowel to compensate for uneven surfaces can lead to excessive thinset, which adds cost and cure time.
Pro Tip: Achieving $80\%$ Coverage
The goal for floor tiling is $\mathbf{80\%}$ mortar coverage under the tile (and $\mathbf{95\%}$ for wet areas like showers). After placing your first few tiles, lift one to check the coverage. Adjust your trowel angle (closer to $45^\circ$) or use a larger notch size if coverage is low.