FlameSafe® FSM 22 Mortar Seal FlameSafe® Mortar/Large Opening Data Sheets: (MSDS, PDS, etc…)Product Data SheetEnsures a Gas-Tight, Smoke-Tight Seal for Large Openings FlameSafe®) Mortar Seal is the most cost-effective endothermic firestop material available for projects with many large openings. It is a lightweight, low density product that is mixed with varying amounts of water to produce the proper consistency for pouring, pumping or troweling into the cavity. Common plaster machines may be used to mix and pump into large openings. Mortar Seal is a paintable product that does not shrink and when cured ensures a smoke-tight seal. It has a zero flame spread and does not contain solvents, asbestos or silicones. It produces virtually no toxic fumes or smoke when burned.