Sikaflex-221 is a high-quality multi-purpose non-sag 1-c polyurethane sealant/adhesive  that cures on exposure to atmospheric humidity to form a durable elastomer.  sikaflex-221 bonds well to a wide variety of substrates & is suitable for making permanent elastic seals of high adhesive strength. Suitable substrate materials are wood, metals, metal primers & paint coatings (2-c systems), ceramic materials & Plastics. Meets approvals ASTM C920 types sikaflex-221 is tested & classified in accordance with ANSI/UL 723 "test for surface burning characteristics of building materials".