A Wise Waterproofer Once Told Me, "Bill, Water Has Nothing But Time On It’s Hands

The pictures above are of a deck in Thousand Oaks; I was bidding the job and took the first picture on the right when inspecting the job. You can’t miss the dirt and water pond stains where water pooled by the scupper area without draining. The picture on the left shows what we found when we stripped the old deck coating off…The real bitch was that the plywood is soft, and I couldn’t tell when stepping on the deck during inspection because…the plywood is 1 1/8″ thick plywood!
There was so much damage to these decks underneath, a lot of plywood at a huge additional cost ($60.00 a sheet for materials alone!) needed to be replaced and the customers budget was blown out of the water, no pun intended…
It appears to me that water sitting for extended period sof time was able to percolate down through the deck coating over a 15 year or so period to cause the damage you see.
Today’s lesson (and guiding principle in building low slope roof decks) learned is, “No water may pond on a deck for more than 48 hours after cessation of rain.”
Learn the lesson or pay the cost.