most water/rot resistant plywood?

[roger wiegand]

The 8' x 24 ' trailer I use to haul and display my fairground organ has leaks I've never been able to find and fix. I've solved 95% of the problem by building a building to store it in most of the time. Unfortunately the water has rotted and delaminated a lot of the floor (to the point of one hole big enough to fall through), so this winter's project is to replace the floor. It's going to be a horrible project as they built everything on top of the floor so I'm going to have to substantially disassemble, try to jack various parts up, and slide new plywood in under the walls and such (all while working around 2500 lbs of organ). Needless to say I never want to have to do this again. The rest of the trailer is all aluminum on a steel frame; this is the only wood.

The orange borg "exterior grade" plywood the manufacturer used was clearly a disaster, so my question is what is the best, most water and rot resistant plywood I can use to replace this floor? I'm not concerned about cost, so relatively exotic suggestions are welcome. I've heard rumors of a phenolic impregnated plywood used in horse trailer floors, but can only find a coated product that will still admit water at the cut edges. Will "marine" or "aircraft" plywood offer any advantage? I'm a little concerned about possible reaction between pressure treated ply and the aluminum structure-- I'm not up enough on the electrochemistry involved to know if that's a problem. I've thought about wrapping the edges with butyl flashing tape, the leakage seems to come inside the walls, with primary rot at those edges, but I'm also concerned about just trapping water with the tape.

I'd love to find and fix the leak(s) but unfortunately the number of hinges and openings may well preclude doing that perfectly. Keeping it inside all the time would, of course, defeat the purpose.

So suggestions on the most durable plywood or equivalent would be most welcome.

327135

[roger wiegand]

In answer to one of my own questions, high copper pressure treated products react quite quickly with aluminum, so I think pressure-treated ply is out of the picture.

[Greg R Bradley]

Should be no problem in MA to find Marine Plywood. Supplier should be able to give you specifics. As long as you can pick it up to avoid shipping, Starboard might be worth considering. It should be easy to find anywhere there is lots of marine construction or even boat repair.

That is an incredible organ! Wow.

[Mel Fulks]

Marine ply is good but real expensive. MDO (medium density overlay plywood also good and expensive. You can take the type of plywood you used before and glue light canvas to it and then paint it,extremely durable . Buy it as "cotton duck" in fabric store .Been used for centuries and has a long history in carnivals and circuses and marine use. Paint and caulk the plywood edges with a top grade caulk like NP1. Job is really not difficult since you can glue up more than one piece at a time by putting plastic sheets between pieces to make sure they don't all stick together. Glue can be Titebond 2 or 3 or UF .

[Dave Anderson NH]

Marine plywood will work fine if you can get it in 3/4". The key here is that it must have a finish on it or it will suffer just like regular plywood. It is the waterproof adhesive for the laminations that make it marine grade. Personally I would use a 2 part epoxy paint and give it at least 2 coats. I emphasize 2 part since HD sells a one part epoxy paint that is of questionable durability.

Another option is regular exterior grade plywood with an outer layer of the thin aluminum sheets that are covered by a baked enamel paint. Sorry, but I forget the trade name.

[Brian Tymchak]

+1 on the MDO (or HDO even). they use it for highway road signs. I would think it will hold up fine for your floor. Seal edges and paint with an exterior finish.

[Pat Barry]

You guys think MDO would be a good choice for flooring on a trailer? I wouldn't use that. I would rather use a couple layers of treated plywood - ie - 2 layers of 1/2 inch plywood. I was not aware of a reaction between treated plywood and aluminum but if that's true I would rather put a barrier such as roofing felt in between the aluminum frame and the plywood. I built a trailer years ago with treated plywood and its been outdoors for just about all of them summer and winter and there is no rot in it at all. Of course its sitting on a painted steel frame.

[Wade Lippman]

I had a similar situation a few years back. I used marine plywood and waterproofed with penetrating epoxy. Then I painted with marine paint. It has held up well.

[David L Morse]

Have you considered extruded Aluminum? It costs a lot more than plywood but you can't beat the performance.

[Shawn Pixley]

I had a similar situation a few years back. I used marine plywood and waterproofed with penetrating epoxy. Then I painted with marine paint. It has held up well.

This is what I would do. Epoxy (and Fiberglass) over Marine Plywood. Works for boats!

[Mel Fulks]

Marine ply will certainly work ,it's made to be in water and can not have any voids whatsoever, it's quite expensive . I don't think it has any advantage over the canvas and floor paint. A year after treating two walk boards in near constant use by masons there were no bare spots. It also has the advantage of providing a little traction.

[roger wiegand]

I've been looking around more and am now pretty sure there's nothing that is completely impenetrable -- except perhaps an aluminum deck, I still need to explore what that might entail. Sounds like the key is going to be edge sealing everything with a penetrating epoxy. I'm also further investigating things like HDO, Euro Form and FinnForm coated plywoods that are used for concrete forms. They are probably pretty waterproof on their surfaces, but the cut edges are exposed. Marine ply from Okoume, sapele, or Meranti seems like a good possibility and is available locally. It has very thin plies like baltic birch so is about as much glue as wood.

I like the canvas idea, but am concerned because I need to get this back into tight slots that 3/4" ply is coming out of. I'm going to put a hardwood floor down on top of this subfloor to create a nicer finished appearance.

Thanks for the suggestions.

[Greg R Bradley]

I've been looking around more and am now pretty sure there's nothing that is completely impenetrable -- except perhaps an aluminum deck, I still need to explore what that might entail. Sounds like the key is going to be edge sealing everything with a penetrating epoxy. I'm also further investigating things like HDO, Euro Form and FinnForm coated plywoods that are used for concrete forms. They are probably pretty waterproof on their surfaces, but the cut edges are exposed. Marine ply from Okoume, sapele, or Meranti seems like a good possibility and is available locally. It has very thin plies like baltic birch so is about as much glue as wood.

I like the canvas idea, but am concerned because I need to get this back into tight slots that 3/4" ply is coming out of. I'm going to put a hardwood floor down on top of this subfloor to create a nicer finished appearance.

Thanks for the suggestions.
With that added wrinkle, how about just using Apitong shiplap trailer flooring? We pay $3.6 per foot for 1-1/8"x7" shiplap and use on commercial flatbed trailers. It holds up in sun & rain and stands up to the daily abuse of hauling commercial freight. One the lowboys has it and it holds up well hauling heavy construction equipment. 16,000 psi strength makes in wear more like aluminum than wood but it cuts and drills like wood. It is hard on tools and the splinters are double nasty. Other than that it works like wood.

[Mel Fulks]

The "duck" is the lightest canvas and the construction one good side ply is a 1/32 shy of 3/4 and you could lightly bevel bottom side of plywood. Since its easier to glue cloth on all pieces at once ,joints can be covered with a piece of canvas about 4 inches wide. Does not show at all with a pattern stenciled on to surface and shows little with solid color. Ask an old carny!

[Mike Cutler]

"I've heard rumors of a phenolic impregnated plywood used in horse trailer floors."

Not a rumor. It's the flooring for a Brenderup Horse Trailer. ( I own a Baron TC. )The only supplier I know of in the US is Mountain Top Trailers in New Hampshire.
It's not just a phenolic resin impregnated piece of ply though. It's a phenolic composite core, with a structural cloth and resin exterior.
The parent corporation also own Thule, so any trailer place that can repair a Thule trailer may be able to get the same material.

Personally though, you need to coat whatever flooring product you use in that application. Any plywood core can be covered in an epoxy resin and cloth.Even using fiberglass resin and some .5 oz, S-cloth will do. Kevlar weave and epoxy resin will give you a floor that will last for decades. You can also source IPE, T&G it, and then put resin and cloth over it.
After it is replaced, no matter what method you use, see if it can have a Line-Ex coating sprayed on the underside. ( Line-Ex is the material used in spray in truck bed liners.)

[Wade Lippman]

Marine ply from Okoume, sapele, or Meranti seems like a good possibility and is available locally. It has very thin plies like baltic birch so is about as much glue as wood.


They are very expensive, but have a good strength to weight ratio. That probably isn't so important to you. Marine fir is going to be much cheaper. I have had some outside for two years, edge sealed with penetrating epoxy and painted, and it is like new.

[Mel Fulks]

I think some of us didn't really catch that we are discussing a SUB floor. I'm guilty. To get any one to notice a traditional hardwood floor in that situation ....you are going to have to paint the machine beige. Regardless of how good the sub floor is ,it seems to me mold and mildew are going to be a problem with hard wood floor.

[Tom M King]

What span between "joists" is there? There are various flooring choices for horse trailer floors (Rumber for example), as well as standard building supply stuff like synthetic decking that might work if the spans are not too great.

[Lee Schierer]

While you are looking at replacing your floor, there are a couple more things that you need to take a look at. Your floor is being supports by framing; therefore, give some thought on what is supporting your floor. Moisture is your enemy, providing ventilation under your floor and possibly adding drainage if there is excess water under your building. A properly installed concrete floor can last several lifetimes.

[Mike Null]

I would look into using pressure treated deck material. I rebuilt my deck 3 years ago using this material from HD and have been pleased with the look and durability.

[Jerome Stanek]

I would look into fiberglass reinforced panels like they use on semi trailers.

[Ole Anderson]

My new 4 place enclosed aluminum snowmobile trailer uses PT exterior ply. Pretty much an industry standard for snowmobile trailers. My 14 year old enclosed aluminum 2 place trailer, which my son now has, shows no sign of rot.

[Jason Roehl]

If cost is no object, I'd say +1 on the aluminum. Get diamond tread.

[roger wiegand]

I wish I'd known about the aluminum decking when having the trailer built! I'm trying to think about how it could be retrofitted, it's thicker than the plywood and appears to come primarily in planks not sheets. I still haven't quite figured out what is critical for structure, I'm afraid the floor may well be integral to the structure-- the big hinged panel on the side of the trailer appears to be primarily attached to the floor, rather than directly to the frame, but I haven't yet got it far enough apart to be certain of that. It also appears that the walls are primarily attached to the floor and via the floor to the frame. It's not yet obvious how the floor is attached to the frame, I haven't found a fastener yet. Obviously more demolition and detective work to be done before I fully understand the problem. I hope to really tear into it the week after Christmas.

The frame has crossbars 24"OC, but additional structure welded in directly under the organ.

The flooring I'm thinking of is not a real hardwood floor, but rather a prefinished engineered product, perhaps even a "look of real wood" vinyl tile. I can't afford the additional height of hardwood as the top of the organ only clears the roof by less than an inch.

I really appreciate all the suggestions, this has given me a few new avenues to pursue. This is clearly going to be an "interesting" exercise.

[Jason Roehl]

Thicker than the plywood? I was thinking something like this:

http://diamondlifegear.com/diamond-plate-aluminum.htm?gclid=CI7d-LXf4skCFYGCaQodtA4DCg

Looks like you would want either 1/8" or 1/4" thick. Metal decking of any flavor doesn't need to be as thick as plywood.

[keith wootton]

simpson plywood makes a hdo marine plywood called skidguard in two surface confiurations. both designed to finished floor surface. one is a embossed pattern in the paper overlay, and the other is 36 grit sandpaper. you may not need any other product over it, but you will have to treat edges and penatrations. the patterned comes in at least 1/2/, 5/8, and 3/4, and the grit in 3/4 and ? keith

[Kev Williams]

Get the cheapest but strong enough plywood you can find that will work. Get a gallon or two of coal tar epoxy and give that plywood a coat or two, typically goes on 10 mils thick per coat, 150 sq. feet per gallon... After it's dry, paint it white or beige or whatever.

Coal tar epoxy is a 2-part 4-1 mix epoxy, it's relatively cheap ($50-$60 a gallon), it's thick, it's ugly black, and nothing will get past it. Nearly every steel hulled boat on the planet is painted with it. If it'll keep the sea and ocean salt water away from a steel hull, it'll keep a little rain from getting into your plywood. :)

[cody michael]

While you are looking at replacing your floor, there are a couple more things that you need to take a look at. Your floor is being supports by framing; therefore, give some thought on what is supporting your floor. Moisture is your enemy, providing ventilation under your floor and possibly adding drainage if there is excess water under your building. A properly installed concrete floor can last several lifetimes.

do you have any examples of trailers with concrete floors? seems like that is not an ideal use for concrete....