Marine Plywood - what is it and where do I get it?

[Aquaman01]

Hi,
I have some boat modifications to make this year, and they will require marine plywood. What makes marine plywood so marine, and where do I get it?

Thanks,
Rob

[upnorth]

Marine grade plywood is resistant to water and seperation. I believe they use special glues to keep it together.

Most of the lumber yards should carry it. It is used a lot for the floors in bathrooms and such where some resistance to moisture is needed.

[Surface Tension]

If you call it "marine grade" plywood you would get a better understanding.
No core voids, no knots.
Wood can differ from fir to mahogany to teak. There are different grades and they use a British Standard or BS. Differing grades would be which wood is used, rot resistance, thickness of plys and number of plys.

[icatcher]

Rum river lumber and hallberg marine carry it.

[waterwolff]

prepare for sticker shock because they are pretty proud of it

[Borch]

Very proud of it. But again you get what you pay for(usually).

I know there was a period not too long ago you could get the stuff here in MN because of the chemicals used to rot/insect infestation. Sounds like that is not longer an issue,

[Big-Al]

I paid $47 for 1/2 inch and $63 for 3/4 (special order at Billman's in Duluth) in March of '01 for a boat project. I questioned the need for this over regular treated, but decided to go all out. The surface was very high quality. I think you pay for that as much as the water resistance. Great for hatches, door panels, etc., but wonder if regular treated would be just fine for floor. It takes stain and varnish really nice.

[This message has been edited by Big-Al (edited 01-01-2004).]

[Aquaman01]

Big Al - which one swelled on the floor - the marine or the regular treated?

I need it for a floor, a couple of bulkheads and some hatches/seating.

Thanks, ya'll -
Rob

[Big-Al]

The marine swelled although it was a very small amount, but any amount bothered me seeing as how this is what I had installed as the floor on my boat. It did it just along the very edge that was sitting in direct contact with a damp garage fllor in the spring. I certaily did not expect it.

[Big-Al]

The 32+ year old floor I replaced in my Lund was NOT marine plywood, but regular treated. I have had some people tell me (I'm sure no expert) that regular treated may even last longer than marine. Marine has two surfaces that are sandable, stainable and sealable. Because of this I think it has a different treatment process. The leftover pieces that I have discolored and swelled on the edges where they are in contact with my damp garage floor. I didn't like the looks of that.

Do we have an expert out there that really knows the story on this stuff?

[JWB475]

I gutted and rebuilt my boat last summer and used treated lumber instead of the marine grade.

Reason #1, cost.

Reason #2, my boat is always covered and only gets wet if I am fishing in the rain. It also tends to dry out pretty quickly so the plywood isn't wet for very long.

Reason #3, even treated plywood will out live the carpet that I put on it. If I still have the boat when the carpet needs to be replaced I can then address any bad areas where the treated plywood is starting to separate.

I don't think marine grade plywood is necessary, I could replace the flooring and platforms 3x over in my boat with treated plywood for the cost of marine plywood, but that is just my opinion....

[BLUESHARP]

A good sealer or resin over treated lumber works well.

[letsfishjeff]

A .6 Foundation treated plywood is cheaper than marine grade and they use it for wood basements in ground. That is available at most good lumber yards.

[Steve Bakken]

OK. Here's the story straight out of the horse's mouth. Out of the hundreds if not thousands of boats we have had apart NOT ONE boat has had marine grade plywood in the floor. The only place I have ever seen true marine grade used on a boat is on wooden bench seats such as those found on the more basic Lund models and in some cased on the dash panels on some older console style boats. Why they don't use it on the floors I'm not totally sure. I know one factor is definitely the cost, others may be ability to absorb paint and carpet glue. I don't know. I also have never seen green-treated wood, mainly because of the fact that it is so prone to warpage. and it is a little more brittle to work with. What all of the boat manufacturers use or have used that I have ever seen in a boat floor is standart BC or AC-grade plywood. The same stuff that you can get in any lumber yard. I've seen this stuff shot in as little as 5 years and I've seen it last 20+ years. It all has to to with the type of care the boat receives. This is what we use, and in 20-some years, we have never had one come back. For all you do-it-yourselfers out there, one thing that we do when we replace a wood floor, is to seal the whole top side with fiberglass resin before installing the carpet. This ensures that any water that does get on it will stay in the carpet layer and evaporate more quickly. My advice-- if you can get 20+ years out of standard AC or BC plywood with proper care, it's not worth the extra cost and hassle to try to get the marine grade.

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Steve @ Bakken's Boat Shop www.bakkensboatshop.com

[muchowja]

Marine plywood is 7 ply whereas the stuff you buy at the lumberyard is 4 or 5 ply. As far as I know that is pretty much the only difference.

[Aquaman01]

Wow - outstanding info! Thanks to all of you! I believe I will go with the AC plywood with a resin coat.
Thanx,
Rob

[tightlines]

Pick up the .60 below grade green treated. It is designed for underground application. Contractors have been using it below ground for years already with no rotting problems. It is a lot better than the standard .40 green treated and is less expensive than marine grade. Most quality lumber yards carry it. I know Menards, Fleetfarm and Lowes here in Fargo did not carry it. Got it at Crane Johnson. Little better lumber yard.