J-B Weld Blue Silicone Gasket Maker Sealant is an RTV (Room Temperature Vulcanized) Silicone gasketing material designed for use in mechanical assemblies, sealing and bonding uneven surfaces. Upon curing, which occurs when the product is exposed to the moisture in air, the silicone forms a tough, waterproof seal on most surfaces. It will not shrink or crack, resists weathering, is sensor safe and is great for many automotive applications.