Setting tile? Ultraflex 2 LT Large-Tile Mortar with Polymer, White is the thinset that goes between your tile and the substrate. Built for large-format and heavy tile (12×24 and up) where standard thinset would slump or sag under the weight. Non-slump on walls, no lippage on floors. White color so it doesn't telegraph through translucent tile or light grout joints.