https://www.homebuildingandrepairs.com Click on this link for more interesting construction and home improvement videos. This video will provide you with a method that might work for your exterior deck, especially if the floor joist or decking joist are protruding from a building or cantilevering and creating a waterproofing problem. You should check with local building contractors and building authorities before using this repair or weatherproofing information to verify whether or not it can be used in your particular area.