TEC™ Full Flex® 15035025 390 Series Premium Thin Set Mortar 50 lb White. TEC™ Full Flex® 390 Series Premium Thin Set Mortar 50 lb White. A premium general-purpose mortar designed to be used in a wide range of applications over plywood cementitious surfaces and other substrates. Known for superior handling and engineered for dependability Full Flex® Premium Thin Set Mortar is a contractor favorite. Designed for use over a wide range of interior or exterior new or renovation substrates in residential to extra heavy duty commercial applicationsit offers one step mixing smooth and easy spreadability prolonged pot-life extended adjustability time and excellent coverage making Full Flex® a practical real value.