Many factors should be considered when selecting the right trowel size for a tile installation, but the most important factor is the tile size. As a general rule, after tile is pressed into mortar, mortar should cover the entire back surface of the tile without voids or trowel lines. So, take time to check for proper mortar coverage by periodically lifting a couple of tiles and inspecting them for coverage. If there are voids or trowel lines showing, a larger-sized trowel may be required for the installation. Back-buttering is generally recommended for tiles with any side 15″ or greater. Installations of tiles larger than 24″ x 24″ typically require the skill of a knowledgeable and experienced tile installer. The Technical Data Sheet and product packaging will provide mortar coverage for common trowel sizes.
Note: When using premixed products such as MAPEI Type 1 or MAPEI Premium Mortar for tile and stone, using a larger trowel can greatly extend the drying time of the mortar or adhesive.