Description Mapei Ultraflex Rapid Set Tile Mortar with Polymer 25lb Gray Premium Rapid-Setting Tile Mortar with PolymerUltraflex RS is a premium-grade, single-component, high-performance, polymer-modified, rapid-setting thin-set mortar for interior and exterior installations of tile. This mortar has a high content of unique dry polymer, resulting in excellent adhesion to the substrate and tile. Ultraflex RS is a FastTrack Ready product, allowing grouting in 2 to 3 hours. It can be used for both interior and exterior installations of tile in most residential floor and wall applications. In commercial applications, use on interior floor and wall installations and exterior floors. Ultraflex RS meets or exceeds ANSI A118.4 and ANSI A118.11 requirements for fast-setting mortars when mixed with water.