Ideal for use on large, rusted-out metal, cracked or shattered fiberglass. Long 'N Strong is a long strand fiberglass filler that is designed as a super strong, long-strand reinforcing compound used for restoring and repairing Metal, Aluminum, Fiberglass, Wood, Masonry, and Concrete. The extra long strands of fiberglass allows for maximum bonding power and unparalleled strength.