Floor replacement Options - OSB vs Plywood.

[Oliver P]

I am at the point now where I need to glass in my new floor. I have read many posts on these boards and the consensus is that OSB sucks.

I was at Home depot yesterday to check plywood availability and noticed something that I have not heard mentioned before. The OSB for a given thickness was much stiffer (more resistant to bending) than its plywood counterpart.

The OSB in general was also much flatter than any of the plywood that was being sold.

From what I have read online the glues now used in OSB are the same as exterior or marine plywood. Many of the moisture related issues have also been solved.

BTW- my plan for the floor will have 6 oz glass cloth epoxied to both sides of the floor so water intrusion is not that much of an issue.

I have always wondered why Scamp chose to use OSB. I wonder if it was the stiffness of the product.

So, what do you think. Is OSB the great evil???

[Scott B.]

OSB is far superior in strength and flatness, unless it gets wet then is swells like a sponge and falls apart. I prefer plywood, and if you go to a better grade of plywood around $25 per sheet then you will find it is nice and flat and a good product, Plywood is also easier to bend if you need to get it in. Of course this is my opinion.

Full disclosure: I am in the process of replacing the floor in my Burro with plywood.

[Greg A]

I'd recommend Marine Plywood if you are going to all the work to replace. Since you're in St Pete FL you should have no problem obtaining Marine Plywood.

[Oliver P]

I'd recommend Marine Plywood if you are going to all the work to replace. Since you're in St Pete FL you should have no problem obtaining Marine Plywood.

Hey Greg,

I understand that the marine ply is superior for the weather resistance. I am more worried about the lack of stiffness from marine ply vs OSB. The reason I am replacing now is because of failure of the floor to body join caused by movement (broken tongue). I think the stiffness of the osb might increase the strength of the whole trailer... No??

[Andrew Gibbens]

I understand that the marine ply is superior for the weather resistance.

Not really. Marine plywood has two differences from exterior ply: it doesn't have voids in its inner plies and its outer plies won't have any repair patches in them.

The glue used on marine ply is the same WBP (water boil proof - it is tested by submersing a sample in boiling water for one hour) glue used in exterior ply.

The absence of inner voids is important for boats as they would attract moisture when one side of the plywood is immersed in water - if your trailer floor is like that, I suggest rot of the floor isn't your biggest worry!

The absence of outer skin repair patches looks nice, but doesn't improve durability.

Andrew

[Darwin Maring]

Have U thought of 3/4in thick preasure treated ply? Would be solid and rot resistant and your glass covering would be a barier on both sides.

[Raya]

I was going to say what Andrew did - I agree.

As far as the stiffness goes, if you are fiberglassing both sides, the sandwich construction will add quite a bit to the stiffness. Just to give you an example, boat decks are often cored with balsa wood, yet they are stiff due to the fact that the skins are in tension and the whole affair acts like an I-beam.

Your frame should also be providing some support, I believe.

I wouldn't recommend treated ply, as I don't think it would mix well with fiberglass/epoxy. Also, in my experience it's not a very good grade of ply.

The fiberglass skin on either side, and good tabbing bonds to the shell - along with epoxy resin and a good grade of fiberglass - will probably result in a floor that is better than what came from the factory. The glasswork I've seen on most eggs is just chopped strand mat and polyester, which is quick and economical, but nothing to write home about in the strength department.

Raya

[Donna D.]

I wouldn't recommend treated ply, as I don't think it would mix well with fiberglass/epoxy. Also, in my experience it's not a very good grade of ply.

And I wouldn't recommend it (treated ply) because it's a carcinogen! Warning, warning, warning. ALWAYS wear a mask when cutting this stuff. And wash your hands really well after handling.

Remember when people didn't think asbestos and vermiculite was dangerous?

[Oliver P]

Have U thought of 3/4in thick preasure treated ply? Would be solid and rot resistant and your glass covering would be a barier on both sides.

I do not want to increase the thickness of the floor ply due to weight issues. I am trying to stick to the 5/8 nominal size that was used originally.

The OSB that I took out that I think is original was very well held together. Just destroyed over the tongue where the break happened.

I also understand that new OSB is not the same animal from 20 years ago.

Thanks for all the input everyone.

[Paul from NWOnt]

Go back to your lumber yard, and grab a sheet of each. Right away you should notice a significant difference in weight.

I've always liked wood for it's resilience, and generally the glue negates that aspect.

Scamp uses OSB, so perhaps it does have some benefit.

[Andrew Gibbens]

Scamp uses OSB, so perhaps it does have some benefit.

Cost?

Andrew

[Oliver P]

Looks like it was decided for me. No OSB in the thickness I needed. The Depot had nothing close to the right thickness.


Lowes had what I was looking for. The original OSB measured at 0.595". Lowes had an exterior grade "B" non-Pt ply measuring at 0.600" 6 ply.

Seemed quite stiff too.