ARDEX X 77 Fiber Reinforced Tile and Stone Mortar is a high-performance, microfiber-reinforced, polymer-modified mortar formulated especially for large format tile installations. Use to install porcelain, glass, quarry, ceramic and most natural stone tiles* over interior or exterior concrete and masonry floor and wall surfaces. Also use for interior applications over exterior-grade plywood. ARDEX X 77 is ideal for use in swimming pools and fountains and over in-floor heating systems and is recommended for all tile sizes, including mosaics.