All purpose UV resistant Sealant. Applications include interior and exterior sealing especially those exposed to sunlight. Suitable for wood, fiberglass and metal. Sikaflex®-521 UV is a multi-purpose, UV resistant, non-sag, elastic, one part silane-terminated polymer sealant, which cures on exposure to moisture. Solvent and isocyanate free. Not intended for use on EPDM or TPO RV roof membranes. UV 505 is the direct replacement.