An exterior finish that is prone to failure is a “waterproof” membrane that has been placed on an outside deck. If the deck is placed over living space with the intent of keeping that space dry and protected then it is even further prone to some measure of failure over time. We have tried a wide variety of repair products for these decks over the years. Many of the different waterproof decking systems, or repair coatings, even the ones that we used, would fail over time. Many of these systems carried the claim that they would work on completely flat surfaces as well. It has been our experience that , with time, water will find it’s way through ANY flat surface NO MATTER WHAT. Recently, however, we have had great success with three different systems that share a common concept in their design. It used to be that the waterproofing membrane itself was the final finish and fully exposed to the weather. When used in traffic areas like decks, the membranes breakdown prematurely. The newer systems are much better because what makes them work cannot be seen on the surface and is protected from the elements by a durable surface that can be maintained (i.e., re-coated periodically). They also all require some positive slope in their application so that water cannot be left to puddle on them.
In some roofing membranes such as rubberized asphalt, also known as Modified Bitumen or “torch applied” roofing , or in TPO single ply roofing, the membranes do quite well when exposed. They have been designed for full exposure; however, most often there has not been a proper flashing provided for the maintenance of these membranes. Like most roofing systems they have a specified time that they are designed to last. When they wear out, the entire exterior cladding has to be removed in order to place the new roof behind the wall finish.