What type of plywood is best to use for the subfloor?

[solarstream]

I've seen some mention of marine plywood with an epoxy or if you're super gung-ho I think I saw one guy put POR15 on his marine plywood.

What is marine plywood anyway? I called my local lumber yard and they have it in 1/2 and 3/4 but Lowes and Home Depot don't even seem to know what it is.

And sorry if "floor finishes" isn't the right place to post this. I looked for someplace for asking about "sub floors" but didn't see one.

Thanks.
Solarstream

[Alumination]

Marine plywood is generally made of high-grade veneers with no voids and uses waterproof glue. Many non-marine plywoods contain voids and are made with a water-resistant glue only. For a floor replacement marine plywood is a good choice. You may want to waterproof the wood surface as well, which is what the folks using epoxy and POR-15 are doing.

[barts]

All commonly available plywood is made with waterproof glues now.

Here's a useful link:

Frequently Asked Questions: Products | APA - The Engineered Wood Association

Generally, marine plywood is overkill for Airstream floors.

Sealing the completed floor is probably a lot more important than making sure that there are minimal voids in the plywood; I'd spend the $$$ on epoxy rather than a better grade of ply. The normal failure mode of Airstream floors is water damage and rot; marine plywood is just as susceptible to this as good quality exterior plywood.

- Bart

[SteveH]

Although I've never had to replace a floor, I agree with Bart on this....the danger is in the rot, not delamination. I'd seal the wood with the Epoxy and use normal exterior plywood.

[Melody Ranch]

CDX and seal it. Marine is overkill.

[Klatawa]

We have just replace the floor in our new project a 1965 tradewind. I used 3/4 marine plywood because of better material with no pops or voids. If you are planing to put some type of flooting floor over the plywood voids and pops won't be a concern but if you plan on puting tile or lunoleum on the plywood you do not want any voids or pops. Murphys law will take effect and where you step if there is a void or pop you will have a hole or dent in you floor. Some lenoleums are expensive and a good base is a must for a smooth floor. I also found the the original floor thickness in our 1963 Safrai and the 1965 Tradewind where 5/8". Hope this helps in your project.

Dave

[barts]

Note that A/B exterior plywood is available; it has the same lack of surface voids as marine plywood, but is not as suitable for bending to tight radii as marine ply...

Talk to your local lumber yard; Home Despot is fine for a small patch piece, but if you're doing big sections, get better stuff - it's worth it.

- Bart

[nickmeloy]

Would pressure treated plywood be an acceptable candidate for this application? I believe that pressure treated material can still be sealed with epoxy, etc. as an additional aid. For a given thickness, the weight per square foot will probably be greater than non-pressure treated plywood.

[ZoominC6]

Non at all in my opinion. Google ADVANTECH SUBFLOORING and see what you think. I've used this stuff for years and it's virtually indestructable though a bit heavier than plywood. Good luck.

[markdoane]

Originally Posted by nickmeloy

Would pressure treated plywood be an acceptable candidate for this application? I believe that pressure treated material can still be sealed with epoxy, etc. as an additional aid. For a given thickness, the weight per square foot will probably be greater than non-pressure treated plywood.

Don't use pressure treated plywood. The old arsenic based pressure treatment was corrosive toward aluminum, but the new copper based treatment is 5 times worse.

[BLL17]

Dear Bart, do you know if it is okay to use 15/16" subfloor? I wanted to use Nylaboard but after using your post it seems better to use plywood ... the nylaboard is recommended by eco people for non toxic allergy issues. but the company is going out of business and all they have left is 15/16" thanks

[bel73]

Originally Posted by ZoominC6

Non at all in my opinion. Google ADVANTECH SUBFLOORING and see what you think. I've used this stuff for years and it's virtually indestructable though a bit heavier than plywood. Good luck.

Advantech is used inside enclosed snowmobile trailers. Some also use a product called Rainblock. Both are designed to get wet and guard against rot.

[OTRA15]

For the slightly higher cost, marine ply is worth it IMO. If not available, exterior A/B and/or PTS (plugged touched up (?) and sanded). Coating all surfaces of the cut pieces with epoxy is also important IMO. WEST System is good. Very important to coat the cut edges of all plywood pieces before installation. Coat the full sheets with epoxy before cutting it up, then coat the cut edges later.

Definitely NOT CDX ply, as the interior voids can come back to haunt you with pronounced weak/soft spots under the finish floor material, unless . . .

If you are going to put another layer of underlayment plywood on top of the sub-floor plywood, and then linoleum or strip flooring, maybe CDX is OK, but why save a few pennies when you are fabricating a $50k to $150k investment?

Do it right the first time!

[AWCHIEF]

If I was going to go to all the trouble and expense of replacing the floor I would use a modern composite product. I still cannot figure why (other than saving $$$) why Airstream continues to use plywood.

[OTRA15]

The plywood approach may offer some weight savings over composite materials, some of which are very heavy (lb/sf). Also plywood is stronger for point loads (footsteps for instance) than many composite materials, if you compare the same thicknesses.

[barts]

Originally Posted by BLL17

Dear Bart, do you know if it is okay to use 15/16" subfloor? I wanted to use Nylaboard but after using your post it seems better to use plywood ... the nylaboard is recommended by eco people for non toxic allergy issues. but the company is going out of business and all they have left is 15/16" thanks

You'll run into a difference in weight, and the door will be slightly easier to hit, but for a frame-off the thickness of the subfloor will have little impact.

Personally, I find plywood a nice material to work with, but opinions vary .

I'm a strong believer in protecting the plywood surface from water damage; a couple of coats of epoxy & paint on the top surface will really help if your trailer should develop a leak that's not immediately detected. Painting the frame (or using roofing tar on the top, but that's messy) will help prevent
problems should that area get wet. Wet steel rusts, and the rust attacks the wood.

I would also redesign the rear hold down plate to avoid the obviously bad design that leads to rear-end separation. Keeping water away from the plywood/steel interface is important; I used stainless steel to replace the steel angle plate.

- Bart

[OTRA15]

Originally Posted by barts

. . .
I'm a strong believer in protecting the plywood surface from water damage; a couple of coats of epoxy & paint on the top surface will really help if your trailer should develop a leak that's not immediately detected.
. . .

Per Post 13 on this thread and Posts 5 and 9 on the following thread, I recommend epoxy-coating both sides of the plywood full sheets, plus all the cut edges of each plywood piece before installation.

http://www.airforums.com/forums/f461...xy-137415.html

Post 7 by RareStream on the thread above confirms the wisdom of coating all the cut edges IMO.