I have a deck that needs to be re-planked. I've seen it suggested that, instead of deck planks, one could use marine-grade plywood as a flooring. If so, it seems that this would be both lower material cost and easier install. Is this true? Are there disadvantages? Are there guidelines for such installations?
Marine plywood is not that different from CDX plywood they use the same glue and pre press process and hot press cure process.
The main difference is in the veneer used , tight knots , with the core plugged so there are no voids compared to cdx. Even marine plywood needs to be protected from water so you will be adding a paint or other material on top , drilling holes for drainage creates places for water entry Into the core. It may sound like a good idea I would just about guarantee it won’t last as long as a dimensional lumber surface with a simple stain. Have you priced 5 quarter marine ply? I don’t think you would want a deck made out of anything thinner than 5/4 and that may be pushing it. If it freezes in your location don’t use it, the water will penetrate the wood and when it freezes it will come apart.
Again the difference is in the quality of the veneer and by the time you go thick enough and seal it you would do better with a wood or composite product.
I think marine plywood is not treated and therefore not nearly as rot resistant as standard decking materials which may limit the lifespan of the deck. The slope may have to be steeper than you would think so water runs off the plywood especially if valleys form over time.
That said, it’s a pretty interesting idea.