Rectorseal 66019 Metacaulk 835+, 5 gal.Rectorseal 66019 Metacaulk 835+ is a 1 component, fire rated elastomeric silicone sealant for through penetration firestops. Prevents flames smoke gas water spreading through penetration openings. Silicone based use in systems where dynamic movement is expected. Features STC rating 55 as well as FBC System Compatible indicates that product has been tested, and is monitored on an ongoing basis to assure chemical compatibility with FlowGuard Gold,