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Old 05-25-2017, 11:02 PM   #1
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Subfloor material

I am considering doing a complete replacement of the rotted out subfloor with a shell on restoration. Am I crazy? If I am starting from scratch what type and thickness of material should I use? Regular plywood, MDF, marine treated plywood? I have seen several threads suggesting that Coosa composite engineered panels offer a lot of advantages over traditional wood but don't much about this option. What are the advantages and disadvantages of using something like Coosa. See www.coosacomposites.com. I know that they are more expensive and won't rot or mildew, but are they difficult to cut, install, cover. Etc
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Old 05-26-2017, 08:15 AM   #2
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Welcome to the Forums!

What year and model of trailer do you have?

There are lots of threads discussing the merits of alternative subfloor materials. Try doing a google search from outside the forums using search terms like "airforums coosa" or "airforums nyloboard" or just "airforums subfloor" and you should get lots of hits. I can sum it all up as follows, though. The non-wood alternatives are usually rot-proof, but also very expensive, sometimes heavy, and usually hard to acquire. They may survive longer than the rest of the trailer (especially the rust/disintegration prone frame), but what is the point?

Marine plywood isn't called marine plywood because it is any more resistant to water, it is all about the layers and the voids--overkill for a subfloor.

My recommendation is use conventional plywood and seal it up with a few layers of polyurethane, especially on the edges at the "endgrain." The stuff you have probably lasted 30 years, had it been sealed up in the first place, it would probably be fine right now. If you want to spend extra money, then get plywood with a "sanded" side that is completely smooth and free of voids. Install it nice side up, and you will save yourself a lot of work when it comes time to make it perfectly smooth prior to installing your flooring.

As far as thickness goes, just measure your existing floor thickness and match it. It is a little inconsistent historically, some people report having 5/8" in the same era that others report having 3/4" floors. You have to match what you currently have or the holes in the front hold-down-plate won't line up again, and the plywood won't fit under walls the way it should.

I think you are doing the floor replacement the hard way by doing it with the shell on. If your floor is rotted, then your frame probably needs some repair as well. Search for "airforums gantries" and join the shell-off movement! There are a lot of things you can do with the gantries that will make the whole process a lot less painful.

Now for some uncsolicited advice: You can spend a lot of time researching the "best" materials and reinventing the wheel. This usually results in scope creep and analysis paralysis. Choose the tried and true techniques you find here on the forums, and get to work while you are still enthusiastic about the project. There are lots of half finished rennovations out on Craigslist that probably got bogged down in a research project.

Good luck!
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Old 05-26-2017, 09:11 AM   #3
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Has anyone had any experience with this material? I saw it several days ago at H. Depot and checked out the 3/4". It seemed fairly rigid. Of course it is much more expensive. I am not sure of the tensile strength as compared to pine plywood of the same thickness.


http://www.homedepot.com/p/3-4-in-x-...0361/205080747
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Old 05-26-2017, 09:55 AM   #4
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I am not sure that the PVC panels are structural. PVC tends to get brittle over time. I think knot free plywood that is coated on the edges and top with urethane is the way to go. There are things that can be done like sealing the C-channel and putting drains in. Removing the plate at the rear that causes so many problems is another. Getting leaks stopped is something you need to do regardless. Sealing the new floor with carpet or vinyl is a bad thing and it traps water and hides the fact that is it there till it is too late to do anything about it.

Perry
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Old 05-27-2017, 09:19 AM   #5
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The description says its for walls and ceilings. It may not be structural. But on the flip side, 3/4 inch is thick and may work. I'm going to assume that this stuff is expensive. I do like a lot of the qualities that it has but good plywood may still be the best option. Sometimes great things are achieved when one gets out of the box.
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Old 05-27-2017, 10:56 AM   #6
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After quite a bit of research, I found this. Joubert Okoume Mahogany marine plywood to be the best product for my sub-flooring. 18mm (3/4") 11plies https://www.wolstenholme.com/plywood...arine-plywood/.
https://www.marine-plywood.us/mahogany_okoume.htm.


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Old 05-27-2017, 10:58 AM   #7
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Unites States Plastic Corp makes this product and their pricing runs ~$565 a sheet. Curious, what kind of deal did Home Depot offer?
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Old 05-27-2017, 11:46 AM   #8
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The mahogany plywood looks nice but how much does a sheet cost? Ok let's just say you find an indestructible rot free sub floor product. If you change nothing else the aluminum parts will corrode. The steel frame will corrode. The interior of the trailer will have mold growing in it. 90% of rear sub floor problems are the plate at the back of the trailer that can be removed and most of your leak potential goes away. I put a new floor in mine in 2011 and it is just as dry as the day I installed it. I also removed that hateful plate that goes under the back of the trailer.

Perry
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Old 05-28-2017, 01:02 PM   #9
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The pricing on the PVC 3/4 " sheeting at H. Depot was listed at $74.00 for a 4' X 8' sheet/ They also had 2' X 4' and 2' X 2' sheets.
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Old 05-28-2017, 01:31 PM   #10
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That's a descent price. Maybe a good alternative in the front and rear pieces where most of the rot occurs. Most sheets of plywood in the center sections are good even after 30 or 40 yrs. the rear hatch, doors and windows are where most leaks occur. If this stuff can handle a 2 foot span and hold its rigidity it's worth a shot. No rot is great! Uv exposure should not be an issue as long as you cover it with flooring
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Old 05-28-2017, 03:42 PM   #11
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It is probably particle board with a pvc coating. If so, not good. Just use Douglas fir Plywood (good one side). Coat the bottom with a coat of wood preservative before you install and it should outlast the trailer. It is also very strong.
No matter what you use, you have to keep out the water.
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Old 05-28-2017, 11:27 PM   #12
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I checked and it is definitely solid PVC. This is not the PVC core plywood. I agree it would probably be best in areas that are prone to rot such as the rear and possibly at the door area. My only concern if it were used in a high traffic area would it sag over time.
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Old 05-29-2017, 05:51 AM   #13
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Quote:
Originally Posted by David C W View Post
I have seen several threads suggesting that Coosa composite engineered panels offer a lot of advantages over traditional wood but don't much about this option. What are the advantages and disadvantages of using something like Coosa. See www.coosacomposites.com. I know that they are more expensive and won't rot or mildew, but are they difficult to cut, install, cover. Etc
As someone that has replaced their own subfloor with Coosa I can tell you first hand what it is like to work with.

You can machine it just like any wood product, using any and all woodworking machines; jigsaws, table saws, routers. It leaves a beautifully machined edge if using a saw or router.

As you have found out it is 40- 45% lighter than plywood; will not rot, promote mold or mildew and is just as strong or stronger than plywood. I placed a 6" by 4' strip across two saw horses and stepped onto the middle. It supported my 260 lbs, so I started bouncing.......about 8-10 bounces later, it finally cracked; not broke.

I used the Bluewater 20 board but the Bluewater 26 maybe better for your application.

Live life care free, knowing that any leaks into your walls will not harm or damage your subfloor for the rest of your trailers life time.

As for cost; your investment in Coosa will reap dividends when it becomes time to sell, as you will be able to demostrate to a prospective buyer that your sub floor is pristine by dropping a piece of Coosa into water.

Cheers
Tony
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Old 05-29-2017, 06:55 AM   #14
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How much does a sheet of that stuff cost? They make the Coosa board close to me. I could drive to Bham and get some. I don't plan on doing any major work to my trailer but it might be good for other projects. I remember fiberglass boats where not really fiberglass and they would rot.

Perry
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Old 05-29-2017, 08:42 AM   #15
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Nearly all the rot in my 68 was along the back and in areas where there were leaks from vent stacks. Water is the enemy. I would say use a good quality plywood, coated all the edges (top and bottom in a 4 inch band) with a good epoxy sealer (West System). The floor is a structural component and wood is a proven product. Since almost all the rot in my trailer was along the edge, any future leaks should not have such a devastation effect since there is an epoxy barrier coat and the end grain is sealed. In my opinion fixing the leaks is much more important than the type of wood used. Eventually the failure points may start leaking again but if the wood is treated with a good sealer, damage will be minimal and it will take many years to destroy the floor. There will be plenty of other things to spend money on, trust me on that.
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Old 05-29-2017, 09:11 AM   #16
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Originally Posted by perryg114 View Post
The mahogany plywood looks nice but how much does a sheet cost? Ok let's just say you find an indestructible rot free sub floor product. If you change nothing else the aluminum parts will corrode. The steel frame will corrode. The interior of the trailer will have mold growing in it. 90% of rear sub floor problems are the plate at the back of the trailer that can be removed and most of your leak potential goes away. I put a new floor in mine in 2011 and it is just as dry as the day I installed it. I also removed that hateful plate that goes under the back of the trailer.

Perry

Perry, the second link I added has the pricing. 162.00 per 4x8x18mm(3/4").
I also coated the top bottom and edges with epoxy paint. Worth every penny.
Your explanation of the true reason for the rear rot issue on Airstreams is correct. The plate on the rear bumper area that is hinged and has a storage for slinky hose etc. is the problem. That peice that goes under the skin and ends up against the plywood subfloor will allow water to penetrate and thus rot the subfloor.
I eliminated that problem with some 032 aluminum a break and a metal stretcher. I made a 2" flashing, with ends that curve around both sides. It goes between the skin and subfloor and under the hindged top cover. Now I still have my cover for that area. No more water getting next to the plywood at all.
I realize that not every one has access to a metal break and a metal stretcher. However that is my solution to rear end rot and it works.

-Dennis
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Old 05-29-2017, 09:33 AM   #17
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I still have the box on mine but it is a separate compartment and the rear looks very much like the sides of the trailer now. Not as much room as before but enough for the stinky slinky.

Perry
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Old 05-29-2017, 11:57 AM   #18
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From a quick look at the specs the weight savings is approximately 20lbs a sheet. I personally do not think it's worth spending double then marine grade plywood. As a red seal carpenter who works with exterior grade plywoods ( doing formwork, constant exposure to moisture) I see it as a no brainer unless weight savings are critical. As a bonus marine grade plywood is easy to find in any city
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Old 05-29-2017, 07:18 PM   #19
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I paid $70 a sheet for marine grade plywood and I did not see that is was much better than regular plywood. I felt kinda ripped off to tell you the truth. It was not even clear on both sides. It has patches on one side. I think the regular stuff clear on one side is plenty good with exterior glue. The stuff that was in there was not Marine grade but it was at least plywood and not chip board.

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Old 05-29-2017, 07:57 PM   #20
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The one up side of Coosa is that you don't have to spend money or time to epoxy both sides to seal it. Remember, any hole, fastener, bolt that goes through your epoxied plywood board has just opened up an avenue for water to gain access to the wood inside; with Coosa, it doesn't matter and you don't have to epoxy it.
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