Materials, Mortars, and Adhesives
Materials, Mortars, and Adhesives
Large format tile requires mortars that can support the tile's weight and achieve full coverage. ANSI A118.4 (modified thinset) or A118.15 (improved modified) are typical; for LFT, a medium-bed mortar (ANSI A118.4TE or A118.15TE) is often specified because it can be applied up to 3/4 inch thick without slumping. The mortar must be mixed per manufacturer's instructions with the correct water ratio and allowed to slake for the specified time. Using the wrong trowel size is a major trap: for LFT, use a 1/2-inch by 1/2-inch square-notch trowel or larger (e.g., 3/4-inch U-notch) and back-butter the tile to achieve at least 80% coverage (95% in wet areas). The type of tile matters: porcelain has low absorption and requires a high-polymer modified mortar; natural stone may require a specific mortar to avoid staining. Epoxy adhesives are used in food service or chemical exposure areas. Traps: using unmodified thinset over concrete with porcelain LFT; mixing mortar too wet or too dry; forgetting to back-butter; and using the same trowel size as for small tile. Worked example: A 24x24 porcelain tile over concrete needs a modified medium-bed mortar, a 1/2-inch notch trowel, and back-buttering to achieve 80% coverage. If you use a 1/4-inch notch, coverage will be inadequate and the tile may debond.