OSB vs PLY For Floor

[Wobbly Wheels]

...the yacht that was built with osb...

Ferrocement was a craze for a while too: not a particularly good boatbuilding material, but cheap.
Then there's the garbage yachts...


I used OSB for the decking on my utility trailer (build #1). I coated the bottom with gooey black stuff and the top with gelcoat.
I didn't notice any delam or anything in the two years that I used it, but it began to sag pretty bad. That was a single floor though, a torsion box might be different. My own choice (and that's all it is) is to use ply instead.

Anybody used MDO ?
It's the stuff roadsigns are made out of - I made some deck boxes out of it a while back and it seems like it would be ideal for walls or a single skin floor: it's impregnated with a resin to stand up to life in the weather and it has what appears to be a resin-soaked paper backing on the face to put a nice finish onto.

[Big Dave]

I use MDO all of the time, but I didn't feel like spending more then double ($70 for 3/4") to have a pretty floor. The weathering weak spot for all plywood is the edge. MDO is an exterior grade plywood that doesn't need to be sanded to become a nice looking sign. If you were making a non-insulated painted tear it would be ideal. For a floor or inside a insulated wall, regular exterior ply should be fine as you would never see it. Another thing to be aware of is that MDO has a fishy/B.O. type odor when damp. That may dissipate over time, but I've never spent much time living in a box made of it.

Here are a couple demo videos of the Advantech OSB that I'm going to be using for the rest of my build. It's only $24 a sheet at Lowe's. The only downside is having to use PL Polyurethane glue on all joints.

http://www.youtube.com/watch?v=cqL4K6m4kKI
http://www.youtube.com/watch?v=XIgUP98qYp0

[Wobbly Wheels]

Another thing to be aware of is that MDO has a fishy/B.O. type odor when damp.

Thx Dave, my exposure to MDO has been limited so it's good to know that kind of stuff (I used ext on my own floor and have no regrets...so far, anyway)

[working on it]

Unable to find marine-grade plywood here in the Texas interior, I used 1/2" birch plywood as my floor, secured to the trailer crossbeams with carriage bolts and PL adhesive anywhere metal contacted wood. Then it was coated with Titebond, covered with 1/4" moisture resistant luan, and the perimeter Tek screwed all around (dozens of screws). All air-spaces were pressed out before it dried. The bottom of the trailer received 3 coats of automotive undercoating; the top got two coats of polyurethane (no UV problem expected,it will have vinyl flooring covering it). I did this before I purchased any other materials for my TTT, but I would do it differently now. I would just use the 23/32" Arauco sanded plywood that I got for the upper structure (bought 6 sheets at 40% off) as flooring, as well. Listed as ACX "cabinet-grade" at the store, I've now discovered that it also has waterproof (phenolic) glue and is "suitable for exterior use". At 62.6 lbs per 4' x 8' sheet, it is lighter than the birch ply/luan composite I used as floor, and lighter than any OSB I've seen (or used). I see no problem using this as flooring if the surfaces and especially the edges are sealed.

[Corwin C]

Another thing to be aware of is that MDO has a fishy/B.O. type odor when damp.

Thx Dave, my exposure to MDO has been limited so it's good to know that kind of stuff (I used ext on my own floor and have no regrets...so far, anyway)

Having worked with literally thousands of MDO signs, some of which have been outdoors in the weather for 20+ years, that odor when the overlay surface gets wet doesn't go away. I did cut a table out of some old MDO signs and painted it (both to get rid of the smell and make it easier to clean.) I haven't noticed the odor since.

I can also confirm that the untreated edges, when in conditions where they can dry (hanging on a post in open air), will last for 20+ years. Most of those signs I can cut 1/4" to 1/2" off the edge and the wood looks pristine. If it can't dry easily on its own (bolt holes w/ washers & galvanized bolt), it seems to only last 5-10 before delamination starts. There again, realize that I'm in the desert southwest, not the humid environments that many of you are in. Your mileage may vary.

[tamnalan]

My tear's floor and walls are MDO (3/4", with resin/paper treatment on the exterior side only). I finished it a couple of months ago. The only odor I smell is the interior stain/poly i used. I've been leaving it outside so it gets periodic rain where I live in Ohio.

[planovet]

A biscuit jointer would let you easily join two sheets of ply together, or could you find a specialty plywood place and buy a single 5x10' sheet.

That's what I did

[ghcoe]

Choosing Between Oriented Strandboard and Plywood

Good article on the differences of OSB and Ply.

http://bct.eco.umass.edu/publications/b ... d-plywood/

In the article it says that the 7/16 OSB and 1/2 plywood weigh the same. I am using 7/16 OSB for the floor in my build.

[Robbie]

I used the 7/16" OSB for the floor of my 5x8 Benroy. I just ran a support underneath the middle of the center seam and screwed and glued the OSB halves to the sub-floor structure and then coated the bottom with roofing tar and 1" rigid foam insulation. It's worked great and was super cheap!

[Jerry Bleeg]

I used 2 sheets of 5' x 5' x 1/2" Baltic birch sheets, and made the joint with biskets. I like baltic because it is so straight, does not warp to readily, and it came in 5 foot wide sizing. I think I paid about 25.00 per sheet at a cabinet supply shop. So my floor ran about 50.00, which did not seem to bad for a quality plywood. It's kind of hard to bisket join 1/2" ply, so a 1" x 2" under the joint is a good idea. Just watch out for any frame rails. I also used a poplar 1 x 2 down the side of my floor to give me a larger surface to screw and glue my walls. My wall cover my frame. Others attach their wall on top of the flooring. So you should also consider how you will be attaching your wall to your floor. Just think it through.