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Old 04-29-2008, 09:36 AM   #1
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Subfloor material dimension

I'm not sure if anyone has encountered this (or if I'm doing something different), but I removed all the sub floor in my trailer and saved the pieces to make templates from 4x8 sheets of MDF board. I figured this was more preferable than chopping up some expensive permanent material as I negotiated the curves and notches. The sub floor Is 88" wide and (!) 48 7/8" long when you include the dadoed 1" that the two overlapping pieces occupy atop the frame. Aside from wondering why they did this, my question is, do I need to buy 5' x 8' x 5/8" material? I can still use my templates, but will need to add that pesky 1" when cutting the real deal. Any help or suggestions would be greatly appreciated.

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Old 04-30-2008, 10:11 AM   #2
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I used old floor sheet as template and wish I hadn't - I ended up cutting away too much and left gaps that weaken the floor channel to plywood fasteners by placing the clamps too close to the edge of the plywood. I recommend using appliance sized box cardboard mock up templates for end rounds to get it well centered and fully sized...

On my '73 trailer the frame spar crossmembers vary in height to allow for joining plate installation - an 8" wide plywood plate overlapping the joint by 4" each side and then both thicknesses through bolted into the spar so it really doesn't matter where the seam ends up...


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Old 05-06-2008, 07:11 AM   #3
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For what it's worth, I've been doing a little researching on this problem and received this reply from Georgia-Pacific...

Dear Customer,
Georgia-Pacific does not manufacture material wider than 4' in a 5/8" thick panel 8' long. Another option would be marine-grade plywood which is available in 4x8-foot sheets of 1/4, 3/8, 1/2, 5/8 and 3/4-inch thickness. Sheets up to 5x12 feet are also available. Available grades are A-A, A-B, B-B (face-back), MDO and HDO. Marine-grade plywood is not treated with any chemicals to enhance its resistance to decay. If decay is a concern, it should be pressure-preservative treated to an appropriate standard.

The detailed description of veneer grades and Marine-grade plywood is contained in Voluntary Product Standard PS 1-95: Construction And Industrial Plywood.

Although Georgia-Pacific Corporation no longer manufactures marine grade plywood, a few building products companies still do (such as Plum Creek and Roseburg Forest Products). BlueLinx is the distributor for both and they stock both " and " panels. BlueLinx can be reached at 1-800-830-7370 (West Coast).

Thank you for contacting Georgia-Pacific.

I will continue to search for the optimum material for this application and update on my findings.
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Old 05-06-2008, 07:33 AM   #4
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I would not reccomend MDF for sub-floor, due to its tendency to swell once it gets wet,(and it will get wet). I did a fair amount of research on this very subject as I have some sections of floor to replace on my '56. If you are not going to finish the plywood than you do not need to spend $80.00/sheet for AA marine board. You can save your self a lot of $$ and at the same time install a great subfloor by using BCX board. The (X) is the glue (water resistant) that is used in marine grade plywood.
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Old 05-06-2008, 07:48 AM   #5
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We used 3/4" marine grade plywood on our '56. The reason we went with 3/4" instead of the 5/8" (actually 11/16" to match the original) was we took out is the old floor AND flooring which went under the c-channels and since we were doing a shell on installation and couldn't get the flooring under the channel with the wood. So to make-up the difference, we upped the plywd thickness.

I second the opinion to not use OSB or MDF...two reasons, 1) the water issue previously mentioned & 2) the additional weight. They are much heavier than plywood because of all the glue.

We did not need anything wider than 48"...the seams did not overlap in ours, the elevator bolts spanned the gap between the panels. When we did ours, we attached to the frame on both sides of the joint. the butt joints will be filled prior to installing our flooring.

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Old 05-06-2008, 08:34 AM   #6
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I hear you on the MDF problem. I might have been mistaken in my first post regarding using MDF for the templates. I was using 4x8 sheets of a pegboard material (without the holes) that was 3/16" thick. They were very flimsy, but easily cut with a jigsaw. My c-channels were attached to the sub floor with the vinyl tiles butting up to the channel, so I'm pretty well locked into 5/8" thickness unless I want to play find-the-rivet-holes when the shell comes back down. Drag'n, thanks for the heads up on BCX. I was concerned not only with the cost of marine ply, but also the weight. I'm somewhat amused with this little conundrum, since it seems that there are few Ambassadors needing a sub floor out there!
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Old 05-07-2008, 05:00 PM   #7
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I only had to replace a small (20X72) section of the sub-floor .I used 5/8 CDX.Then I dash patched the seams and the voids with fiberglass impregnated Bondo

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