When installing two different tiles in one pattern, use a trowel that can accommodate both.
Twelve-inch square porcelain tiles are used in numerous applications. They come in a wide range of colors, textures, thicknesses and patterns, making them an extremely versatile — as well as durable — floor, wall and countertop covering. When installing 12-inch porcelain tiles, the proper trowel size is important. Tiles need a specific depth of mortar to be beaten into; 12-inch porcelain tiles may be installed using one of several different trowels, depending on the tile itself and what other tiles may be installed alongside it.
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Smaller Multiple-use Trowels
If you are installing multiple types and sizes of tile and need something that will work with 12-inch porcelain tiles as well as smaller tiles that may be used as borders, within a pattern with the 12-inch tiles or in another application being done at roughly the same time, use a trowel that will give adequate depth and coverage with both a 12-inch tile and something smaller. A 1/4-inch by 3/8-inch square notch trowel is most commonly used for 6-inch square tiles, but it is adequate for installation of 12-inch tiles as well. Use this trowel if you need a multiuse trowel.
12-inch Porcelain Tiles of Standard Thickness
If the 12-inch porcelain tiles being installed are of uniform shape and size and are roughly 3/8 inch in thickness, a uniform trowel size can be used. A 1/4-inch by 3/8-inch square notch trowel will provide the right depth of mortar bed to beat a standard-size 12-inch porcelain tile into. A 1/4-inch by 1/2-inch U-notched trowel will also provide a thick, even bed. This size of trowel also works well with tiles that are slightly larger than 12 inches, such as 13-inch squares and 12-inch by 24-inch tiles, or for those jobs where 12-inch tiles are mixed with larger tiles.
Larger Multiple-size Trowels
For tile installations mixing 12-inch square porcelain tiles with larger tiles, installations where one trowel is desired for two jobs, a project with 12-inch square tiles and larger tiles or extremely thick porcelain tiles that are more than 3/8 inch in thickness, a larger trowel size is needed. A 1/2-inch by 1/2-inch square notched trowel gives excellent coverage for 12-inch square tiles, but also provides good coverage for larger tiles as well. A 1/4-inch by 1/2-inch U-notch trowel and a 3/4-inch by 5/8-inch U-notch trowel will also provide the thick mortar bed required for installations with tiles measuring 12 inches or larger or for mixed large tile installations.
The high temperatures needed to produce porcelain tiles can sometimes result in an irregularly shaped tile. The tile may warp or "lip" slightly in the corners, requiring an additionally thick bed of mortar, as well as additional mortar spread over the back of the tile. Some porcelain tiles also have ridged backs from the manufacturing process, which need to be filled with adequate mortar upon installation. These types of tiles require at minimum a 1/4-inch by 3/8-inch square or U-notched trowel to provide coverage. Larger-sized trowels will also provide adequate coverage for irregularly shaped tiles, particularly if they're being installed in a multiple-size tile pattern with larger tiles.