Proper installation of ceramic tiles requires good coverage of mortar on the backs of the tiles. The size of the tile will affect how deep the mortar needs to be, and the size and shape of the grooves the trowel leaves in the mortar.
Therefore, when determining what type of trowel to use to lay your ceramic tile, always pay attention to the size of the tile itself.
Mosaic Ceramic Tiles
Mosaic ceramic tiles, or tiles that measure two inches in size or smaller, require a thin, tight groove for installation. Choose a V-notched trowel for any mosaic installation. Tiles measuring one inch or less in size should use a 3/16-by-5/32-inch trowel. Tiles measuring two inches should use a 1/4-by-3/16-inch trowel, although any V notch can handle mosaic ceramic tiles in a pinch.
Wall Tile and Small Floor Tile
Most ceramic wall tiles measure four inches up to six inches square, and 3-by-6 or 4-by-8 inches in rectangular sizes. Square notched trowels work the best for wall tiles in this size range, and for smaller floor tiles measuring six inches or smaller in size. Choose a square notched trowel that measures 1/4-by-1/4 inches for best results.
Larger Wall Tiles and Small Floor Tiles
Wall tiles measuring six or eight inches square or extended subway tile sizes such as 4-by-12 inches, as well as six- and eight-inch floor tiles can use a square or U notched trowel. Look for trowels that measure 1/4-by-3/8 inches in size in either square or U notch. For tiles that straddle two trowel sizes, use the larger trowel size for tiles that are 3/8 inch or thicker, or that are handmade and have irregular backs.
Large Ceramic Floor Tiles
Ceramic floor tiles come in sizes up to 24 inches square. Use a square notched trowel for any tiles measuring at least 12 inches square and 3/8-inch thick. A 1/2-by-1/2-inch trowel is best for larger floor tiles. For 18- and 24- inch tiles that are 1/2-inch thick, use a U notched trowel that measures 3/4-by-5/8 inches for best results. A 1/2-inch square notched trowel will work for larger sizes, but back buttering, or applying of additional mortar to the backs of the tiles may be required for a good bond.