A white intumescent mastic is a water-based fire-rated acrylic sealant supplied in a standard 310ml cartridge for caulking gun application. Formulated to provide up to 4 hours of fire integrity (EI fire rating), it expands rapidly (intumesces) when exposed to extreme heat or flame, swelling to form a robust insulating char that seals gaps and blocks the passage of fire, toxic smoke, and hot gases. Exhibiting excellent acoustic insulation and adhesion to masonry, timber, plasterboard, and metal, it is designed for sealing perimeter expansion joints, linear gap seals around fire door frames, and small service penetrations in compartment walls and floors.