Metacaulk® MC 150+ is an intumescent, one-component, general purpose, fire-rated sealant and smoke seal for construction joints and through-penetrations. A water-based, non-sag caulking grade sealant that is easy to apply as well as to retrofit. An economic choice for most common applications. Sound Transmission Class (STC) rating 51, Tested in a UL 411 wall assembly/section to ASTM E90.