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Old 01-20-2014, 10:10 PM   #1
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marine plywood vs plywood vs osb

Hi All,

I stopped at my local lumber yard today to investigate the cost & availability of marine plywood vs regular plywood. To my surprise they had marine plywood in 1/2" & 3/4". My original floor is 5/8" osb and I am replacing the forward 5' section. In talking with the salesman about going with marine vs regular plywood he suggested osb. He stated that all the glue used in the osb makes it a better option than the regular plywood and probably as good as marine plywood. I was shocked to hear this from him as most here seem to not go this route. Is he misinformed or is there some merit to this. Anyway, I was leaning to using regular plywood and painting both sides and edges as it comes in a 5/8" thickness that I currently have.

Barry
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Old 01-20-2014, 10:22 PM   #2
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marine plywood vs plywood vs osb

Please do some searches on the marine grade plywood and it's reaction with aluminum. I did and opted for exterior grade fir plywood and painted this with a coat of West epoxy
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Old 01-20-2014, 10:49 PM   #3
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marine plywood vs plywood vs osb

I went with 5/8" ply and sealed it with an all natural tung oil based deep sealant and floor finish (Bio Impression and Parquet both by Le Tonkinois). Since the glue is water proof and it has less voids inside it, Marine ply is good if you're building a dock or live in a super humid area where moisture penetrates the wood from the atmosphere (think the Congo). But for a sub-floor I'm of the opinion that it's not necessary. Even if you go with marine ply you should still seal it--just because the glue won't rot doesn't mean the wood itself won't.
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Old 01-20-2014, 10:54 PM   #4
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Good points on the reactions (corrosion) of aluminum by treated plywood David.

My reaction to the lumber guy recommending OSB is to find a different source of information. Personally I would use the same plywood Airstream now uses on the newer models. Sure it will rot if wet over extended periods but it won't rot if kept reasonably dry; that's where the effort would be.

Painting the surface and edges can work against you. It won't waterproof the plywood and when water does soak it, it will be much harder to dry out to keep it from rotting.

I believe the weakness in Airstream's floor system is the vinyl floor covering and insulation under the subfloor. This system serves well to keep spills and wet feet from wetting the wood, and it insulates the floor, but when exterior water leaks enter under the vinyl and spread it is nearly impossible to dry before floor rot starts.

We use a moisture test meter regularly to probe through the vinyl and find leaks, and it is very effective. Found and repaired four minor leaks since trailer was built 2 1/2 years ago. I have often thought about replacing the vinyl floor covering with something water and dirt resistant, but breathable. Don't know what that would be. A natural oil finish over tongue and grove wood perhaps.
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Old 01-20-2014, 11:15 PM   #5
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We epoxied the top of the plywood (we only patched our floor), with the first coat cut w/ 10% xylene and the next two straight epoxy. We then painted the surface w/ an aluminum moisture cured polyurethane (like POR-15).

This works well and is easy to clean and sweep; we use area rugs over the
painted surface.

Proper marine plywood is just better construction than regular exterior ply; it doesn't have metal salts or other anti-rot stuff in it so should have no corrosion issues.

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Old 01-20-2014, 11:35 PM   #6
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With any laminated wood, whether OSB, interior plywood, exterior plywood, or marine-grade plywood, two major components are involved, the wood and the glue.

Marine-grade and exterior plywood and some OSB have glues which do not let loose when they get wet. The glue in interior plywood will lose adhesion when wet.

Nearly all of the wood used will rot (fungal attack) if continuously wet or subject to being repeatedly wet. Some wood types (redwood and teak, for example) are more resistant to rot.

So, you can have glue that holds up to being wet, but most woods will not. The solution is to keep the wood dry or, if it gets wet, make sure it dries out quickly.

As for helping wood dry out, elsewhere (http://www.airforums.com/forums/f36/...ml#post1379524) is a note mentioning what we have done.

Tim
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Old 01-20-2014, 11:59 PM   #7
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I think the key here is to NOT use "green tinted" wood. The green tint, I know as Wolmanized comes from copper nitrate applied to the wood. When copper and aluminum come into contact they create a battery, not good for the aluminum. Not all wood preservatives use copper nitrate. Olympic Stain Wood Preservative comes to mind.

On a similar thought, not all wood rots readily. For instance, heartwood douglas fir is fairly rot resistant, as is white oak, and western red cedar heartwood. All have been used for fence posts in years gone by. I have never heard of OSB being antifungal. You should definitely do some more research on this one.

On my own trailer, to protect the plywood, I flooded it with Olympic Stain Wood Preservative until it would no longer absorb it. Then I let it dry for several weeks. Water does not soak into the wood now. It's been 10 years since I did it and it still looks like the day I did it. It is going to have a very long life indeed.

I'm thinking about building my own tonneau cover for the "new to me" pickup I'm planning to purchase. I'll sure use marine plywood in the construction, if I can find it .
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Old 01-21-2014, 06:46 AM   #8
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Let me see… laminated wood sheets glued together with waterproof glue or chips of wood compressed together. I really do not know which would be better...
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Old 01-21-2014, 08:22 AM   #9
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I used AdvanTech for my Bambi II flooring. AdvanTech Moisture Resistance | Huber Engineered Woods

I've had a piece of it outside for about a year now & it looks the same as the day I put it out there. I'm ready for the boos, but I like it!
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Old 01-21-2014, 08:46 AM   #10
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OSB is made by compressing the wood flakes and glue at a high temperature. When OSB is exposed to water the compressed wood chips swell and destroy the integrity of the panel. OSB is also heavy in comparison to plywood of the same stiffness. OSB has low nail and screw holding properties.

Exterior plywood is made with waterproof glue. Marine plywood is made with about the same glue but with better internal plies to make joints in it stronger and more water resistant. Both will decay. The treated plywood is very corrosive to steel and aluminum.

My choice for patches to my floors is exterior plywood and to fix the leak. Both my trailers have the original OSB floors and have had leaks. The damage in OSB is severe in the area of the leak but seems more limited in area compared to the pictures of rotten plywood.
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Old 01-21-2014, 11:10 AM   #11
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Structurally Plywood is stronger then OSB.

Seeing how the body is attached to the floor, Plywood would have the edge over OSB.

Cost wise Plywood is more expensive then OSB, that said I would be inclined to make floor repairs with Plywood, be it exterior or marine non treated then coat it with something like Thompsons water seal around the outer foot and edges on both sides.
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Old 01-21-2014, 11:17 AM   #12
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I had a 1986 Sovereign that hat OSB flooring. It fell apart like wet cardboard where the trailer leaked. It wouldn't even be a consideration for me.
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Old 01-21-2014, 12:24 PM   #13
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He is misinformed

Quote:
Originally Posted by bweldon View Post
Hi All,

I stopped at my local lumber yard today to investigate the cost & availability of marine plywood vs regular plywood. To my surprise they had marine plywood in 1/2" & 3/4". My original floor is 5/8" osb and I am replacing the forward 5' section. In talking with the salesman about going with marine vs regular plywood he suggested osb. He stated that all the glue used in the osb makes it a better option than the regular plywood and probably as good as marine plywood. I was shocked to hear this from him as most here seem to not go this route. Is he misinformed or is there some merit to this. Anyway, I was leaning to using regular plywood and painting both sides and edges as it comes in a 5/8" thickness that I currently have.

Barry
Hi Barry,
The salesman has obviously never seen how OSB fails in an Airstream. You'd be better off to use a quality 5/8" plywood. I prefer to use Joubert.

No matter what you use, you must fix the leaks that caused the OSB to disintegrate.
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Old 01-21-2014, 05:27 PM   #14
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Thanks for all the replies everybody. I kinda thought he was a little misinformed about the osb. Its amazing the amount of information on the site from members. I must have read over a 1000 threads and still learning. Thank you all. On a side not, I did have the trailer sealed up 9 months ago shortly after I got it. It was the first thing done as that is the standard recommendation here. This was done at the local Airstream dealer (not so local at 250 miles away). When I pulled back the curbside skin just in front of the door, the lower insulation was sopping wet and water was pooled up on top of the c-channel. This is adjacent to the area where my floor rot is. I have a call into the dealer about this so we will see what they say about still having the leak after having considerable money spent to use the Seal-Tech & seal everything up. I know these leaks can be tough to find sometimes. Thanks again for all the input.

Barry
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