FortiFlash Butyl Joist Guard is a self-adhesive butyl flashing membrane that provides a layer of moisture protection on the tops of deck joists and beams, prolonging the life of the entire structure. As moisture runs off the decking surface between the deck boards, it can sit on the surface of these structural supports. Moisture can also penetrate into the holes where screws and nails have been inserted, resulting in rot and reduced deck life.

FortiFlash Butyl Joist Guard is made with a self-sealing butyl-based adhesive that performs better at high temperatures than asphalt adhesives and won’t drip onto outdoor spaces or patios below the deck.