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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?

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    One Disadvantage is that there is nowhere for water to go.
    – Alaska Man
    May 12 '20 at 0:07
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    Maybe ! A deck sloped enough for water not to pool would not be comfortable to stand on. Drilling holes in your expensive plywood exposes the untreated interior of the plys and takes time.
    – Alaska Man
    May 12 '20 at 0:13
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    You clearly have not priced marine plywood if you think this will save money! May 12 '20 at 0:50
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    This is one of those ideas that seems, on the surface, to be interesting enough to think about. However, you'd want to ask yourself why this isn't done regularly if it's cheaper and easier. If you do end up with this, I'd strongly suggest a finish that includes an anti-slip component. May 12 '20 at 1:28
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    After answering I looked to see what I could find. 75$ for 3/4” was the cheapest I could find AA or AB, I did not look long but enough to see other manufacturers With the lower grades than the company I worked for We’re selling. you would be no better than an exterior plywood’s with up to 1-1/2 voids in the lower grades and if 3/4 at 75$ sounds good with the flex it won’t last . I would not use it and add all the other comments not to would be sound advice.
    – Ed Beal
    May 12 '20 at 15:04
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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.

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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.

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    I’d think wet plywood would be slippery to walk on...especially if it has a pretty good slope. I think it’s a bad idea.
    – Lee Sam
    May 12 '20 at 0:51
  • You are correct that marine grade plywood is not treated (with the exception of the quality of the veneer) it is the same as Exterior graded plywood.
    – Ed Beal
    May 12 '20 at 18:17

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