Waterproof Your Deck Our self-adhesive, non-skid deck flashing tape is waterproof and weather resistant. Designed to withstand extreme weather., it blocks out water, air and moisture. Super Sticky Permanent Seal Our Butyl Deck Joist Tape forms a permanent seal that is 100% waterproof and airtight, create an under deck waterproofing system protects your deck from Moisture and Rot. Easy to Install Cut, peel, and stick. Joist tape is easy to apply and manipulate to fit your project. Simply cut the tape to the desired length, peel the backing, and apply it to the surface.