We formulated 3M? fire barrier watertight sealant 1000 NS as a single component, neutral cure, silicone sealant. This ready-to-use sealant cures upon exposure to atmospheric humidity to form a flexible firestop seal that helps control the spread of fire, smoke and noxious gases before, during and after exposure to fire. When properly installed, this watertight sealant provides up to 3 hrs protection in tested and listed systems and meets UL water leakage test, W Rating - Class 1 requirements for systems tested and listed in accordance with ANSI/UL 1479. We designed this non-slump firestop sealant as a re-enterable and repairable solution primarily used on vertical surfaces.