Master Bond MasterSil 981-LO is a two-component silicone designed for high performance bonding, sealing, and encapsulating applications. It does not require air for curing. The system features a flowable viscosity and a forgiving 1:1 mix ratio by weight for ease of handling. It is a minimal exotherm material with an extended open time of approximately 3–4 hours. MasterSil 981-LO is also noteworthy for its soft Shore A hardness, offering a low modulus and good flexibility. MasterSil 981-LO cures at ambient temperature in 48–72 hours, or more rapidly in 2–4 hours at 135–165°F. For optimal performance, an initial overnight cure at room temperature followed by 2–4 hours at 135–165°F is recommended. The system is 100% reactive, containing no solvents or diluents, and exhibits minimal shrinkage upon cure.