ARDEX X 90 OUTDOOR™ MicroteC3 Rapid-Set, Flexible Tile and Stone Mortar is a revolutionary innovation in mortar technology that is formulated with specialty, high-performance ARDEX cements, polymers and microfibers to deliver maximum protection against the harshest weather conditions and provide the highest levels of efflorescence resistance for exterior tile and stone applications. ARDEX X 90 OUTDOOR can be installed over substrates with temperatures as low as 40˚F (5˚C) and can withstand driving rains or be grouted in only 2 hours.