Tile sizes have an extremely large range, from three-eights-inch mosaics up to 16-inch and larger squares. To properly hold these tiles in place, particularly in wall applications, the correct depth of mortar must be achieved for each size.
To get the mortar to an even, correct depth, the right size of trowel must be used for each size of tile. Generally, the larger the tile, the larger the trowel needs to be to accommodate it.
Mosaics have a unique installation process. Once the mortar has been keyed, or grooved, to the correct depth, it must be flattened to produce a smooth surface. This prevents excess mortar from seeping between the many grout joints involved in a mosaic sheet. Therefore, use a V-notched trowel to provide depth and an easier surface to smooth. Use a trowel sized three-sixteenths by five-thirty-seconds of an inch for tiles 1 inch or smaller. Use a trowel sized one-quarter by three- sixteenths of an inch for mosaics measuring between 1 and 2 inches.
4-inch and Small Subway Tiles
Traditional wall tiles typically come sized in 4-inch and 4 1/4-inch squares. Newer tile sizes have started to expand on subway tiles to include sizes such as 2 by 4 inches and 2 by 6 inches. These tiles can be installed using two shapes and sizes of trowel. A one-quarter-inch square notched trowel is adequate for installing these sized tiles, particularly for installations that mix these sizes of tile with larger tiles. The best size trowel to use for traditional wall tiles and smaller sized subway tiles, however, is a one-quarter by three-sixteenths of an inch V-notch trowel.
Mid-Sized Wall Tiles
Wall tiles sizes have begun to grow larger as new mortars allow better grip and trends begin to move toward larger tiles with fewer grout lines. This means that many wall tiles now include mid-sized tile sizes such as 6-inch, 3-by-6-inch, 4-by-8-inch, 4-by-12-inch and 8-inch squares.
To accommodate their larger sizes, these tiles may be thicker than smaller sized wall tiles, or may also be used for floor use. Therefore, larger sized trowels are needed.
For larger subway tiles and 6-inch square tiles, a one-quarter-inch square notch trowel is adequate. A better trowel to use, however, is a one-quarter-by-three-eighths-inch square notch trowel. This trowel also provides the best coverage for 8-inch tiles as well.
Alternatively, a one-quarter-five-sixteenths-inch U-notched trowel can be used for all these sizes of tile.
Large Wall Tiles
It is not uncommon to find wall tiles in sizes of 12 inches, 16-inches or 12 by 24 inches. These tiles are typically at least three-eighths of an inch thick and may be up to half an inch thick to accommodate their large size. Therefore, the largest sizes of trowel must be used to ensure proper mortar depth. A one-quarter-by-three-eights-inch square notched trowel can be used for 12-inch wall tiles. For thicker 12-inch and larger tiles, a one-quarter-by-one-half inch U-notch, one-half-inch square notch or three-eighths-by-five-eighths-inch U-notch work best.