The trowel style and measurements for a given tile job depend on a number of factors including the adhesive, the type of tile, and the size of the tile. Each job must be decided upon individually. General guidelines to follow choosing a trowel can be followed in most cases. Trowels that have evenly spaced square notches in them produce a ribbed pattern that ensures uniform thickness of material and complete contact with the tile. Smaller tiles with smooth backing do not need the same amount of setting material to bond that larger texture backed tiles do. Tiles that do not absorb moisture easily do not have much surface tension so they require enough mortar to encase the edges of the tile as well as the tile backs. Trowels with a V shaped groove are used with unsanded adhesives where the tiles are beaten in more firmly. Square notched tool designs are mostly used with thin-set mortars that have a sand component.

It is of vital importance that the back of the tile and sometimes the sides get complete coverage with the chosen thinset or adhesive. You will need a trowel with a deeper notch in it if the back of the tile is uneven.  You will also need a deeper notch the larger the tile gets.  If you are tiling a wall or if the tile you are using is too large you may need to “back butter” the tile.  Back buttering a tile means to spread the chosen adhesive not only on the surface where the tile will be set, but also onto the back of the tile before setting the tile.  The purpose of back buttering is to ensure full contact with the entire tile. Poor adhesive coverage will result in loose tiles or cracked tiles.  It is also important to make sure you set the tile before the adhesive or thinset mortar has begun to set.  At a certain point the mortar will develop a skin that will no longer adhere to the surface of the tile.  the tile will press into the mortar more like play dough instead of sticking like glue.

Tiles should be firmly forced into the setting adhesive before it cures.  This process is called “beating in.” A nominal 1/4″ by 1/4″ by 1/4″ square tooth trowel nets fifty percent contact at the surface. V grooved trowels can be less than ten percent contact at the surface.  With only ten percent contact the tile will not stick.  Beating in the tile forces the adhesive to make more contact and creates a better bond.

As a final tip,  be sure to ask the salesperson at the hardware store for reccomendations.  Most well trained sales associates should be able to show you which trowel is reccomended for their more popular tiles.  Its up to you from there to judge whether your unique situation calls for something different.