Life offers many items from which to choose, some good and some not so good. This principle holds true to the tile industry in the selection of a trowel for spreading one of the various dry-set cement mortars, a.k.a. thin set mortars.

In the early days of notched trowels, those used specifically for thin set mortars, selection was limited to a 1/4” x1/4” x 1/4” and a 1/4" x 3/8” x 1/4” square notch. Through the efforts of innovative installers and others in the tile industry, today there are numerous trowels available. But which one offers the best results? The answer depends on the flatness of the substrate, the smoothness or roughness of the substrate, the tile warpage, and the depth of the ridges on the back of the tile.

For many years, a large format tile was an 8´x 8”. However, today according to the American National Standards Institute (ANSI) A108.T, “Large Format Tile: A tile manufactured in conformance with ANSI A137.1 having a facial dimension greater than 23in. (584 mm).” With the growth of the tile sizes came the need to apply more mortar to support and bond the tile, hence, larger, and deeper trowel notches. However, this is where the problem lies. To supply enough mortar, the trowel notches have gotten deeper and wider, and a second complicating factor is that grout joint sizes have gotten smaller which limits the amount of space the tile can be moved.

The only way to determine the “right” trowel is to apply mortar using several different trowels until one is found that provides the minimum coverage and transfer to the back of the tile. ANSI A108.5-2.2.3 states, “Contact area shall not be less than 80%, or as specified in the contract documents, whichever is greater. Contact area on all exterior installations or interior wet installations shall not be less than 95%. The 80% or 95% coverage shall be sufficiently distributed to give full support of the tile with particular attention to all corners and edges of the tile.” 

The 2024/2025 NTCA Reference Manual offers a Precautionary Statement on the use of the 1/2" x 1/2" x 1/2" notched trowel which has become extremely popular. “The issue with the 1/2" x 1/2" notch trowel is the distance between the notches. The wide space between the notches makes it difficult, if not impossible, to fully collapse the mortar ridges into the valleys. This is especially true when the specified grout joint is 1/16” to 1/8” which limits the ability to move the tile in the back-and-forth motion as seen in the NTCA Trowel and Error video.” The above image illustrates trowels that can provide the minimum 80% coverage with limited movement.