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Old 05-13-2013, 06:46 AM   #1
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1965 24' Tradewind
Pleasant Ridge , Michigan
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Help choosing subfloor plywood and protection method

Hi everyone, my wife and I are deep into our 65 Tradewind restoration and I am trying to decide on subfloor plywood grade and how to protect it. This site is a VERY useful resource for noobs like us. When it comes to subfloors there are a lot of different solutions.

In regards to material I understand marine plywood has the best water resistant properties. But even marine plywood will need to be coated in some way to protect it from gross water spills/leaks that will eventually rot the board. I guess I am leaning on nicer-grade plywood instead of marine plywood since we will have to coat it to protect it anyway.
  • Am I going to go wrong with any AB/ACX/BCX/CDX grade plywood? Does the wood type matter (Fir/Birch)?

More importantly there are a lot of ways to coat or seal the floor from moisture. From materials (epoxies, polyurethanes, house primer or paint, bed liner) to methods (seal edges only, edges with top sealed, edges with top and bottom sealed), there are lot of combinations.
  • What is the "best" way to protect the subfloor assuming water leaks are taken care of? Like most people we are only interested in doing this once... Until we get another airstream!

Thanks for your help!

Chad & Kir
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Old 05-13-2013, 07:07 AM   #2
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You want exterior plywood. ACX or BCX. The A grade will be the best surface, but since it'll be covered, BCX is fine. Put the B side up as it will have fewer defects. I don't think wood type matters.

We sealed all edges with two coats of oil based exterior primer. And then covered the entire floor, top and bottom, with a coat of primer as well.

Chris
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Old 05-13-2013, 07:18 AM   #3
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Quote:
Originally Posted by Minno View Post
You want exterior plywood. ACX or BCX. The A grade will be the best surface, but since it'll be covered, BCX is fine. Put the B side up as it will have fewer defects. I don't think wood type matters.

We sealed all edges with two coats of oil based exterior primer. And then covered the entire floor, top and bottom, with a coat of primer as well.

Chris
Marine plywood, same grades, might be better, if you can get it. More expensive, though. Same stuff as the exterior plywood (3/4 thickness is 7-ply) but with more water-resistant glue holding it together.
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Old 05-13-2013, 08:29 AM   #4
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I'm not an expert on restoring Airstreams but I personally would not use an exterior grade plywood for the project you are working on. Here's a very good explanation I found on Yahoo Answers

"Pretty much all plywoods normally available from regular timber suppliers are weather-boilproof (WBP) nowadays. It just means that the adhesive is to this specific standard - one which can stand a test of boiling in water for 72 hours without failing.

So there isn't really any such thing as 'regular' plywood other than this, nowadays: WBP is the 'new' regular. If you can still call this new.

Not to be confused with so-called 'exterior grade' or 'shuttering' plywood. Which, while still laminated using WBP adhesives, is of very inferior timber quality and grain. It is suitable for sheds or as the name implies, boarding up derelict sites. This certainly can warp and even crack, due to the poor timber quality and often inadequate seasoning. And it is often warped already. But correspondingly, very low priced.

Marine plywood is a higher grade WBP sheet material which conforms to BS 1088, and so must not only meet the very same adhesive test, but in addition, the laminates (exterior and interior) must all be of an equal thickness as well as being of a timber that is specified as 'very durable' (can stand being placed in the ground for 25 years before decay)."

You might also try finding a product called SuperPly Plywood by Roseboro Lumber. I've used it on projects in the past and have been impressed with the consistency.
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Old 05-13-2013, 08:50 AM   #5
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I used marine plywood on mine and I don't think it is any better than the stuff you get at lowes that is clear on one side and has exterior glue. I used polyurathane to coat the wood on the top and the edges. It is probably better to leave the bottom uncoated accept for a couple inches from the edge. This will make it easier to dry out. Also seal screw holes and any penetrations with polyurathane. Flooring is a big issue because you can't see what it under it. The popular thing to do is use Marmoleum which is going to trap water under the floor if you do have a leak. Actually anything you cover the floor with is going to trap water. Not putting flooring under cabinets and under the bathroom will allow water to eventually evaporate or get out where you can see it.

Perry
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Old 05-13-2013, 08:57 AM   #6
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If you go to your local big box hardware store and order marine grade plywood you will probably get 7 ply douglas fir exterior grade of very good quality. Few if any voids and very easy to work with, about $60 a sheet. Do not confuse this with true marine grade boat building plywood. True marine grade has 12-15 plys, is straight and true, incredibly strong and surprisingly lighter. Its also rediculously expensive, the last I located was over $125 a sheet. the big advantage if you are laying expensive flooring like marmoleum is that no underlayment is usually required due to the superior quality. A lot of the equation comes down to availability and shipping in your area.
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Old 05-13-2013, 09:16 AM   #7
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Thanks everyone. You guys rock.

@perryg114 How can I tell if the plywood is clear on one side and has exterior glue?

I found what the vendor calls AB marine plywood that is 7 ply and has "minimal core gaps" and is made from "fully water resistant bonding adhesive" for $60. Is this not true marine-grade plywood?
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Old 05-13-2013, 09:41 AM   #8
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ACX or BCX would be clear on one side (smooth) and rough on the other side. A is smoother with no knots. B would be smooth but it might have some knots that have been patched. X means Exterior glue. C is rough finish and that is what goes down. I got some of the douglas fur stuff marine and I left some outside and I can't say it held up any better than the cheap stuff. It warped and molded fast.

Perry
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Old 05-13-2013, 10:02 AM   #9
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1965 24' Tradewind
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I guess I'll go with the BCX, since I'm not spending over $100 per sheet and the fake marine plywood will serve me no advantage over BCX.

Thanks for your help!
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Old 05-13-2013, 10:13 AM   #10
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I did the front half of the Caravel's floor in 2006. I used the marine grade plywood and left it bare. We put in carpet (easy to pull out and clean). The floor has gotten wet several times and we just pull the carpet and put a fan on it to dry it, still looks like new.

I also didn't put any insulation under it as insulation holding water against the underside was part of what rotted it out to begin with.

Don't over-think it too much, remember that first floor lasted 40 years. Yours will probably last at least that long.
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Old 05-13-2013, 10:25 AM   #11
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Hi, just joined the forum, been lurking for awhile.

I'm a wooden boat builder and have used a lot of plywood. Most all plywood has water proof glue. "Marine" plywood just refers to a higher manufacturing standard usually, few or no voids in the interior plies and equal thickness plies. Lesser ply will have paper thin face plies. Doug fir is heavy, strong, moderately durable and miserable splintery stuff to work with. I never use it in boats. Better options are Meranti or Okoume plywood. Meranti is 25% heavier than Okoume, more durable and half the price. Okoume is mostly used where strength and light weight is wanted, like a kayak. Both woods look like mahogany. Meranti is sold under the trade names Hydrotech and Aquatech. Either would be good for the floor.


Meranti is a bit lighter than DF and about the same price.


All the wood will eventually rot if not protected from moisture. Modern wooden boats (since the 1970s) have all the pieces coated with two or three applications of epoxy. (I get mine on line from RAKA).


If I were doing all that work, I'd use Meranti, cut all the pieces to their finished shapes, then put two coats on each side while coating the edges each time so the edges end up with four coats. If you later cut holes in the floor put a couple of coats on epoxy on the newly exposed wood.


Also note that plywood isn't usually exactly the thickness it's sold as. American ply is often 1/32 or 1/16 thinner than its 'size'. 1/2" ply is usually really 15/32". Exotic specie like Meranti or Okoume are made to metric dimensions but often sold as an inch dimension. There what is called 1/2" is really 12 mm. Don't know if this matters in a floor replacement.

Atlas, I see you are in the Detroit area. Public Lumber at Seven Mile and I75 carries Hydrotech. You can get WEST brand epoxy at West Marine at Nine and Jefferson. It's good stuff but 2x the RAKA price. It's all pretty much the same stuff in the jug.
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Old 05-13-2013, 11:45 AM   #12
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1965 24' Tradewind
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Wow mcdenny good information!


I went to public lumber, but they weren't very helpful with the size I need. I'll go ahead and re-measure (I measured 5/8" with my calipers). Maybe 3/4" will actually work.
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Old 05-13-2013, 02:36 PM   #13
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ACX or BCX is usually 5 ply and often has hidden voids which can cause problems. The 7 ply douglas fir is much stiffer and has virtually no voids. Well worth the little bit extra to me- I only want to do this once every 40 years or so I couldnt get true marine grade locally without shipping costs nearly doubling the price so I went with the best reasonable option.
Got mine ordered through H.D. easy peasy
tim
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Old 05-13-2013, 02:56 PM   #14
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Wow mcdenny good information!


I went to public lumber, but they weren't very helpful with the size I need. I'll go ahead and re-measure (I measured 5/8" with my calipers). Maybe 3/4" will actually work.
L.L.Johnson in Charlotte, on I69 about ten miles S of Lansing, is a bit of a drive but has much more inventory than Public Lumber. I just looked at their plywood list though and they don't have any 5/8. Everything is 1/2 then 3/4.

You could route an 1/8 deep channel on 3/4 to fit in the frame rails or glue on a 1/8" shim onto 1/2 where it needs to fit the frame.

An unrelated note about plywood, I just read on the Johnson site that there is now a 22% duty on Chinese plywood (Hydrotech and Aquatech) as they were found guilty of dumping.
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