Pensil 300 Silicone Sealant is a one-part neutral curing silicone sealant exhibiting superior performance in applications where sealing apertures in walls and floors are needed to control the spread of fire, smoke, toxic gasses, and water during fire conditions. Pensil 300 Silicone Sealant reacts with atmospheric moisture to form a tough durable seal that will adhere to most building substrates without the use of primers. Pensil products do not contain asbestos or PCBs. Pensil 300 Silicone Sealant may also be used to seal vertical and horizontal joints between metals, masonry, concrete and other common construction materials