Ironically, waterproof decks are where we find the worst dry rot in the shortest amount of time. There is a huge variety of waterproof decks offered by manufacturers and contractors. In Utah, every tile exterior deck that we run into has failed. Water gets in through the grout joints and into the grout bed under the tile. With Utah’s freeze thaw cycles, major failure can happen very quickly. Other waterproof deck systems that we see fail regularly are pre-manufactured sheet products that are installed directly over the deck substrate. These types of products have a seem in them every 4′ and the joints usually fail within a couple of years. The best waterproof decking systems are wet applied products that are mixed and applied on site and no joints are created. Unfortunately, even good decking systems fail when the product is not properly tied into the adjacent exterior cladding.
The reason for failure- Its not the way the deck product was installed, or bad material, its the failure to properly tie into the adjacent exterior cladding on the home or building. All exterior cladding products have a moisture barrier behind it. If the waterproof deck coating does not tie into the moisture barrier correctly, water will get under the deck coating. The waterproof qualities of the deck will keep it from drying out, water is trapped, and the wood framing will rot.
These pictures are a example from a job we did in June 2014 on a home that is 5 years old. For more information and examples of waterproof deck, go to this page of our website- https://rambuilders.com/services/remodeling-and-home-improvement/exterior-decking/