FortiFlash® Butyl Joist Guard

Moisture protection for deck framing

FortiFlash® Butyl Joist Guard

Moisture protection for deck framing

A beautiful deck can significantly enhance the value of a home. But under many beautiful decks lies a serious threat. The structure underneath a deck can suffer moisture damage and rot, even while the deck surface itself is undamaged. FortiFlash Butyl Joist Guard prolongs deck life by protecting the supporting beams and joists.

An Easy-to-Use Solution that Prolongs Deck Life

Today’s composite decking materials can withstand prolonged exposure to the elements. Unfortunately, the lumber used to support these high tech decks is not as resilient. As moisture runs off the decking surface between the deck boards, it can sit on the surface of these structural supports. It can also penetrate into the holes where screws and nails have been inserted, resulting in rot and reduced deck life. FortiFlash Butyl Joist Guard provides a layer of moisture protection on the tops of deck joists and beams, prolonging the life of the entire structure. Butyl performs better at high temperatures than asphalt adhesives, and won’t drip onto outdoor spaces or patios below the deck.

For many years, FortiFlash® has been trusted by builders as the brand of choice for fail-safe waterproofing. This easy to use butyl tape was developed based on the same criteria for effective performance. The result is unsurpassed deck protection from an undisputed leader in the waterproofing industry.


FortiFlash® Butyl Joist Guard installs easily on deck joists and beams.

  1. Make sure the surface is clean; wipe away any debris.
  2. Center the FortiFlash® Butyl Joist Guard on the top of the joist or beam; the edges should just roll down the side about 1/8”.
  3. Completely cover the top surface of each joist and beam by unrolling the tape. Apply firm pressure to ensure good adhesion. Notch at intersections as needed to ensure edges of tape fully adhere.
  4. That’s it. Your deck is protected now!


  • Superior adhesion from latest butyl technology
  • Self-seals around screws and nails
  • Withstands higher temperatures than ordinary tapes
  • Won’t drip like asphalt tapes
  • Can be applied at cold temperatures
  • Easy grip edge makes installation a snap
  • Black surface resists UV and won’t show between deck boards


  • 2” x 50’
  • 4” x 50’