Acetoxy silicone paste which cures on exposure to moisture to form a tough, flexible, silicone rubber gasket.LOCTITE SI 5015 is a blue, acetoxy silicone paste which cures on exposure to moisture to form a tough, flexible, silicone rubber gasket. It resists aging, weathering and thermal cycling without hardening, shrinking or cracking. It is used in covers for valves, timing gears, differentials, oil pans, transmissions, water pumps and thermostat housings.