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Thread: Marine plywood

  1. #1
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    Default Marine plywood

    Where can I get marine plywood from? I'm in anchorage. And is there really a difference between marine and treated plywood?

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    I got mine from Spenard Builders Supply here, so I assume they also have it in Anchorage. I've read debates about the differences, which some claim boil down to more or less voids and fills. Immaterial to me because both still need to be sealed to avoid rot. I went with the marine mostly because if it really is a little tougher, that's what I wanted for the deck I was replacing.

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    Member AKDoug's Avatar
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    Plywood is simply plywood without voids in the inner layers that is built to a standard spelled out by one of a couple rating systems. It is glued together by a non-water soluable glue. There are many types of marine plywood and their rot resistance varies greatly. On it's own, without paint or epoxy coating, it is not exceptionally rot resistant in most cases. What marine plywoods bring to the table is exceptional strength per thickness compared to CDX or ACX plywoods and a very smooth finish surface for applying paint, varnish or epoxy.

    Treated plywood is plywood that has been treated with chemicals, CCA and ACQ being the most popular, to render it long term rot resistant. Unfortunately it is usually done on cheaper CDX grades of plywood. It is difficult to get paint to stick to for marine use and I imagine that it would probably have issues with epoxies as well. It is highly corrosive to aluminum and non-galvanized steel. I personally wouldn't use treated wood on a boat.
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    Quote Originally Posted by AKDoug View Post
    Plywood is simply plywood without voids in the inner layers that is built to a standard spelled out by one of a couple rating systems. It is glued together by a non-water soluable glue. There are many types of marine plywood and their rot resistance varies greatly. On it's own, without paint or epoxy coating, it is not exceptionally rot resistant in most cases. What marine plywoods bring to the table is exceptional strength per thickness compared to CDX or ACX plywoods and a very smooth finish surface for applying paint, varnish or epoxy.

    Treated plywood is plywood that has been treated with chemicals, CCA and ACQ being the most popular, to render it long term rot resistant. Unfortunately it is usually done on cheaper CDX grades of plywood. It is difficult to get paint to stick to for marine use and I imagine that it would probably have issues with epoxies as well. It is highly corrosive to aluminum and non-galvanized steel. I personally wouldn't use treated wood on a boat.
    Good advice there, I had forgotten how corrosive AWW wood can be, we recently replaced some lag bolts in a AWW ledger board as they were zinc plated and in less than a year the chemicals had eaten most of the zinc plateing.
    Big diffrence between "hot dipped" galvanizing and zinc plating.
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  5. #5

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    I got a marine plywood product called Meranti from Hardware Specialties in Anchorage. They have to order it, but it is reasonably quick (typically about 2 weeks I think) and reasonably priced. The quality was much better than anything I saw on shelves, even some claiming to be marine grade.

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    Thanks all for the help and advice.

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    There's a store in Bellingham called Windsor Plywood, if plywood were panties, this would be the Fredricks of Hollywood to a boat builder, talk about a selection, they got it all, teak, mahogany, several varieties of marine grade in several thicknesses. They also have Deckaguard which has a laminated finish. If I was replacing a deck I wouldn't even use plywood, I'd go w/ Divinacell foam. It's a fraction of the weight, glass adheres better to it, you can cut it w/ a utility knife and it's easier to fit cause you can pin it together w/ toothpicks.





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    All good except the foam and glass doesn't hold fasteners well & compresses if you bolt through it, you have to cut out the foam and replace it with solid glass or some kind of filler that will hold/not compress the fasteners. The foam/glass has its place but it ain't good everywhere.

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    One thing not mentioned is that typically marine ply is made up for more layers of ply and of the same thickness. I.e. a marine ply will be 5 or 7 layers of the same thickness, vs. non marine which is often 3 plies or sometimes 3 thick plies with two thin face veneers. Having built a boat out of marine ply, I would not substitute non marine plywood. Also while I've used fir marine ply from Spenard, I really prefer Okume BS1088, much nicer to work with, lighter, less prone to checking, doesn't splinter as much when you cut it, and doesn't absorb as much epoxy when glassing it.

    But it really depends on what you'll be doing with the ply.
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    My application is really pretty simple. When installing my new seats I found the fiber board that the manuf had used has cracked. So I only need two 18x20x3/4 pieces which I plan on covering with marine vinyel then mount my seats on top.

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    Honestly, I bet regular old 3/4 CDX would work fine in that application.
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