Depending on the size of your wall tile, choosing the appropriate trowel is important to properly spread an adequate amount of thinset to the wall for durability and proper attachment. Homeowners often select the wrong size trowel when applying tile, increasing the chances of air bubbles under freshly placed tiles.
Selecting the Size
A general rule for selecting the right size trowel is that the smaller the tile is, the smaller the trowel should be. Trowels come in many sizes and shapes, starting at 3/16-inch to half-inch notches for larger tiles. For wall tiles, thinset is used as opposed to mortar, since it is durable and not as thick as traditional mortar. For walls, select sanded or unsanded thinset.
For mosaic or glazed wall tile, use the smallest trowel, usually 3/16 inch to 1/4 inch V-notch. For marble that is four inches, or lighter wall tile measuring six to eight inches, use a 1/4-inch-by-1/4-inch square notched trowel. Wall tiles that are 12 to 13 inches should be installed with a trowel 1/4-inch-by-3/8-inch square notched trowel and anything larger than 16 inches should use a 1/2-inch-by-1/2-inch square notched trowel.
Once you have mixed the thinset according to package directions, use the proper-sized trowel to scoop out thinset and apply it to the wall. Work in sections that you can complete in five or 10 minutes to prevent the thinset from hardening or drying before tile application. Once you apply thinset to the wall, use the notched portion of the trowel to comb over the entire area. Hold the trowel at a 45-degree angle to apply a consistent amount of thinset to the wall for better tile adhesion. Make sure the entire area is uniform in thinset thickness, and place the tiles onto the wall. Use spacers to make sure grout lines are even, and check each tile as you go to make sure there are no air bubbles underneath the tile. If there are, remove the tile and place more thinset and comb before reattaching.