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Old 07-16-2016, 05:45 PM   #1
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1973 25' Tradewind
Geneva , Florida
Join Date: Jun 2016
Posts: 18
Sub floor replacement

Forgive me if this has been asked before. I am a new member and it's difficult for me to search the threads in my iPhone.

Anyway, the guy who is helping me restore my 1973 trade wind wants to lay the new subfloor longways rather than across the frame. He plans on putting each 4x8 sheet in the center and then cut pieces to fit in each side over the outriggers. He will make sure each board sits halfway on the frame member.

Is this acceptable? Any reasons why we shouldn't do it this way? I don't think structurally it should matter if everything is bolted to the frame? I know we still need to put in boards to build up the crossmembers that sit lower.

We are ordering several new outriggers to replace ones that are rusted out but the center cross members look good so we plan to wire brush and coat with por15 before putting the boards down. He wants to do this to give us a floor to walk on while waiting for outriggers so we can get other things done as well. He won't be fully attaching the boards until we have repaired/replaced the outriggers.

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Old 07-16-2016, 06:53 PM   #2
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1983 31' Airstream310
Hillsburgh , Ontario
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Don't use plywood, use Coosa board; doesn't rot, mildew, absorb water, grow fungus or disintegrate and is 40-45% lighter then the plywood you're planning on using.

I used Bluewater 20, but that was for a motorhome; you may want to go Bluewater 26 for more strength. I also half-lapped my joints by 3/4" so half of one board was under half of the other; that way you only have to used one fastener to fasten both sheets.


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Old 07-17-2016, 05:28 AM   #3
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1973 25' Tradewind
Geneva , Florida
Join Date: Jun 2016
Posts: 18
Yikes the price!

Those coosa panels are close to $200 each. I will need to stick with decent plywood. Seller on Amazon accidentally sent me a quart of clear POR15 rust preventative so I will use that on the plywood edges both sides and coat the plywood that the fresh water tank sits on. It's amazing how much I have learned about this airstream since we started taking it apart! Http://
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Old 07-17-2016, 07:55 AM   #4
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1958 18' "Footer"
Idyllwild , California
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Posts: 397
Not sure about using POR15 on wood. I used West System Epoxy, this is really cool stuff and have using on boats for maybe 35 years or so. You can thin it and clean up with denatured alcohol and they have numerous fillers to make it fit many applications.
I used it on my '58 Traveler to laminate the repairs to my subfloor & then sealed what I could get at with it. The link below also has a where to buy.
1958 California Built 18' #18-4092
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Old 07-17-2016, 08:08 AM   #5
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1974 27' Overlander
Baltimore , Maryland
Join Date: Mar 2016
Posts: 142
So, to address your original question, the original design has some cross-members that sit lower as you mentioned. Those are there so that you have space to fit gussets at the seams between the boards, and the gusset will be supported. You'll notice that the lower crossmembers are exactly where the seams would be. If you change the direction of the plywood, you'll want to put a gusset down the middle to support the seam, but the gusset won't be supported by the frame. The center of your floor will be weaker. Not sure what the advantage of changing the orientation of the boards would be. Why does your guy want to do that?

Also, +1 on the West System epoxy if it's in your budget. I am very happy with my waterproof floor.
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Old 07-17-2016, 08:19 AM   #6
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1973 21' Globetrotter
Houston , Texas
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So, back to the original question of how to lay the plywood. When the trailer was originally built, the plywood went side to side. One benefit is that the floor provides some strengthening for the outriggers. The frame was designed to have the floor laid this way--you will see that some of the cross members are lower than others to allow the "doubler" to be put in place where the sheets meet. The approach your helper is suggesting will result in your main frame rails being riddled with holes put in place to fasten the scabbbed in plywood pieces in place. The frame rails are thin in the first place, and have probably lost some mass over time due to rust. I would not go that way.

It sounds like you are going this length-wise route so you can work on the interior while waiting for outrigger repair. Well, you could just lay down your plywood temporarily, walk on it all you want, and then do the final install cross-wise.

There are plenty of people who put in a floor without lifting the shell, try doing a google search of "shell-on floor replacement airforums" from outside the forums, and you should find some hits. Most people who go this route still install the plywood side to side, but they end up splitting the end pieces in the middle in order to get them in place. My opinion is that replacing the floor without lifting the shell is probably the hardest way to do it, but I understand that people get intimidated with the idea of lifting the shell.

As for materials, there are certainly plenty of materials that are better than plywood, and even plywoods that are better than other plywoods, but you have to figure that your floor lasted 40 years in the first place, had the original sheets had some kind of sealer at the edges, you might not be replacing it now. So use plywood with a decent surface finish (you will want it perfectly smooth before laying your flooring), paint it with a few layers of polyurethane, and you should be fine. Yes, there are better sealers out there, but this plywood will never again see the light of day, and it is the exposure to UV and weather that causes finishes to break down.

Good luck!
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Old 07-17-2016, 08:26 AM   #7
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1972 31' Sovereign
Lexington , Minnesota
Join Date: Feb 2009
Posts: 3,157
In laying plywood lengthwise on the trailer, I would be concerned with what it would do when the trailer flexes going down the road. It seems to me that crosswise seams would flex less, and give more rigidity to the whole frame and trailer. I'm not an engineer, but having laid one of these floors, crosswise would be my choice, even if I hadn't known how it was originally laid. We did do a shell on, and it is possible to get the end pieces in whole, without splitting. We did.
Just my 2 cents...

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Old 07-17-2016, 09:22 AM   #8
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1972 23' Safari
Camas , Washington
Join Date: Oct 2012
Posts: 234
Pam and I did a shell on sub-floor replacement. Not sure I would go length ways, might not be as strong as cross ways, but then I don;t know. here is a link to the floor replacement starts on page 4 to page six I think. Good luck have fun

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