I need a sealer Caulk to fill a approx. 3/8" gap between my Composite Decking boards to waterproof and prevent water from dripping between the boards and going on to a deck below. I want the rain water to flow over the composite decking boards to the edge of the deck and run off onto a roof that will take the water away.
What is the best product for this application? What product will adhere to and seal to Composite Decking?