marine plywood vs plywood vs osb

[TinTin]

Measure twice, then measure again!!

[SSSabre]

I too went with 3/4" marine and coated all sides with West epoxy. Imperfect as this method may be, the subfloor is still likely to outlast me. Regardless of what material you use, if moisture isn't controlled it will eventually cause issues somewhere. If the floor doesn't rot, then the aluminum will corrode, crossmembers rust, mold will develop, etc. Good luck with your project.

1970 Silver Streak Sabre - Model 20

[63air]

Unless you are building a boat you don't need marine plywood . What makes it special and more costly ,is that it is guaranteed to not have any voids between the plys. It has exterior glue but is is not treated. The treated stuff is often called "marine" by untrained big box store sales people and it will corrode aluminum. Buy exterior plywood in a grade other than CDX so you have a smooth side ,coat it with a West Systems type epoxy , and seal any bolt hole with something like 3M 5200 and the new floor will be around a long time.

[Isuzusweet]

Originally Posted by Bob Thompson

I just checked the Coosa at Boat Outfitters. A 4x8 x3/4" sheet........$326 plus freight.

Yes, it can be pricey but I was lucky to deal with a marine supply workshop that used Coosa all the time so they bundled my three sheets in with their order, thus I paid no shipping. Also as I stated, you could get away with going with Coosa on say the outer two feet or so and running plywood in the middle if you wish to save money.

I priced good quality marine ply and was quoted $75.00 less than the Coosa. By the time you buy the West system epoxy to coat the plywood, it works out to be the same as the Coosa but with more hassle and subpar quality compared to the Coosa board.

Yes, as a poster did say, controlling the moisture is paramount but I have a unique problem…….Airstream motorhome before 84 laid down 18" or so strips of vinyl clad aluminum across the width of the floor to act as a barrier to the plywood subfloor. Airstream then siliconed the sheets together to try and seal the plywood floor against the elements. The problem is that the old silicone has let go so my floor is subjected to possible condensation from below. In later models of motorhomes the bottom aluminum or galvanized sheet was one piece.

To each their own, but if you want to do the job just once and never have to worry about it again……….

Cheers
Tony

PS If you ever had to sell your trailer or motorhome and you could guarantee a no rot, fungus, mildew subfloor; do you think you'd get your money back with the Coosa? It would certainly show that you cared what materials you were using to renovate your project. Heck if I were to buy a NEW Airstream trailer, I'd drop the bloody Coosa off at the factory myself.

[Frank's Trailer Works]

Okay, I want to clear something up…

CDX is a very low grade of seething plywood.

treat CDX with copper compounds and it is called treated plywood, not marine plywood. It is green and never flat. It often las large voids. It will react with your trailer.

AC plywood is the highest grade exterior plywood. It generally has all voids filled but not 100%. It is the next grade up from the original Airstream plywood which was BC plywood.

AC plywood will not pass a boil test which a marine plywood will.
Marine plywood uses water proof glues and it 100% void free. It is flat and true unlike any of the grades mentioned previously.

OSB is kind of plywood. It is made of shreds of wood glued together under pressure. It is garbage and will delaminate quickly if exposed to water.

A new form of OSB called Advantix has come out. It uses a more water proof glue and coatings of wax to help repel water during construction.

Coosa is a man made product. It is impervious to water as stated earlier.

[Becky B.]

"OSB is kind of plywood. It is made of shreds of wood glued together under pressure. It is garbage and will delaminate quickly if exposed to water.

A new form of OSB called Advantix has come out. It uses a more water proof glue and coatings of wax to help repel water during construction. "

Spelled AdvanTech:

AdvanTech, Buy AdvanTech, Huber AdvanTech | Huber Engineered Woods

Not the same animal as the 80's OSB. Very dense & holds screws every time.....And doesn't swell with weather for over a year...

[Frank's Trailer Works]

I might have spelled it wrong but I did say A new form of OSB called...
I further say I used about 45 sheet of it as sheathing on my house, but I would never use it as a floor in an Airstream. I have built things with both items and the AdvanTech is not any harder, any truer, any flatter, nor does it hold screws any better than 1980's chip board. It does repel water better however. I will give it that. Hope it works for you and other who have used it.

[Becky B.]

Ok, Frank....ok

[gloran]

When OSB was first produced back in the early 80's, it was a lot stronger and had a better glue. But when the manufacturer were mandated to remove the formaldehyde the product has never been as good, and the glue isn't as strong. The OSB available today can't Absorb any moister with out being weakened.

[r carl]

I wonder what this cost a sheet, seems good stuff.

NyloSheet Styles & Sizes

[calais66]

Only in these forums could there be such an impassioned debate over plywood

[Becky B.]

Lol!

[Isuzusweet]

Originally Posted by r carl

I wonder what this cost a sheet, seems good stuff.

NyloSheet Styles & Sizes

I did check this stuff out but discounted it along with Starboard due to two things…….weight and heat expansion. In other words you could only fasten these boards on the exterior of your trailer and have to leave a gap in the middle. If not the expansion rate would put pressure on the C channel and exterior wall.

Cheers
Tony

[bilby05]

Along these same lines. I am working on our 62 tradewind and see that I need to replace just a bit of the floor: about 2 feet x 7 ft of the front, 2 feet x 7ft at the rear, 6-8 inch by 3 feet at the door and 12 inches by 3 feet on street side behind toilet area. My question: after removing the rotted pieces how to squeeze the new pieces in the space between the frame and the and the wall? Looks like the space is 3/4 thick and goes about 2 inches (will measure more precisely before cutting) back into the space under the wall. In places there are bolts that hold the wall to the frame with the wood sandwitched in between. Right now it looks like I will have to grind off any remaining bolts, remove the belly pan from the areas I need to access and then replace the bolts with the bolts that self drill into the frame. Sound about right, or is their an easier way?
thanks, bill b.

[RM66caravel]

Regular plywood coated with sealant like thompsons water seal is my vote.

[paddle whisp]

good points!