3M™ fire barrier water tight sealant 1000 NS is a ready to use, single component, neutral-cure, silicone sealant that cures upon exposure to atmospheric humidity to form a flexible firestop seal. Our water tight sealants help control the spread of fire, smoke and noxious gases before, during and after exposure to fire. We formulated 3M™ fire barrier water tight 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 water tight sealant provides up to 3 hr 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.