Premium Flexible Mortar System. The Kerabond/Keralastic System is the original and time-proven premium flexible mortar system designed for difficult-to-bond-to natural stone, large porcelain tile and glass-bodied tile. Kerabond/Keralastic System is a high-performance, two-part system: Keralastic™, a second-generation flexible acrylic latex additive, is used to enhance the performance of Kerabond™, which is a premium-grade dry-set mortar. This system has exceptional bond strength, flexural strength, elongation and freeze/thaw durability. To ensure proper flexibility, always use a latex additive when applying a dry set mortar over plywood or to set nonvitreous tiles.