Help choosing subfloor plywood and protection method

[Mixter]

I'm at this same stage too. I went with Marine Ply for $57 bucks each. I've been debating over what to do now.... I do see the point mentioned that my AS is nearly 40 years old so whatever I do should last a long time, BUT my floor is rotton.... AND I would imagine that my floor was rotting for many years based on what it looked like. I dont want that to happen... stinky mildew wood- even once doesnt sound good.

I like the idea of a "penetrating" sealer VS a topcoated Kilz primer or comparable, but not sure which one yet. I've considered something like Rot Doctor, but that stuff is expensive. Although the majority of my rot was in the edges, it does not neccessarily "the perimeter" of the coach. The water damage extended across the coach on the edge attached to the cross members. Therefore, I'd be treating ALL the edges... I'd bet I would use a good 2 gallons which would be $200. I would still probably want to at least prime the middles of of each piece too...

I ran into this product at the industrial adhesives distributor I've been buying my Vulkem from... This has definitely intrigued me... The only down side I can think of is that I dont think anything would stick to it once its treated. i.e. stick down flooring, primer, paint, adhesives, etc. Not sure that's a problem for me, because I think I'm going to ultimately be using a nail down 3/8" real wood flooring, OR a floating Pergo- type flooring. The other thing I was going to do, is use industrial adhesive to attache foam board to the bottoms of the subfloor for insulation, but not sure I need insulation or not- there are many different schools of thought there. If I really want to insulate, I can use fasteners and attach to the frame under the flooring. I guess I would have also liked to see a nice painted wood sub floor when I open the truck and side hatches, I guess I can live with just bare wood if I know it is extremely water repellent.

This stuff was $40 / gallon and has a mineral spirits base. It is breathable, and completely repels water. The guy did a demo for me, and the wood stays completely dry- even in the middle of a Florida downpour- just beads right up.

I can lay out my wood and just spray it down with a little $14 Roundup, chemical resistant garden sprayer from Lowes. Application should be quick and easy.... no other treatments/ paints, etc. I think I can do BOTH sides with 2 gallons. Also, since it should penetrate through my 1/2" ply, any holes I drill will already be sealed.

Awfully tempting... and I pretty certain its the way I'm going to go. Havent seen anyone else in the AForums speak of it, so interested to see if anyone has any experience with it.

I'll be watching!
Mic

[Mcdenny]

Originally Posted by Mixter

I can lay out my wood and just spray it down with a little $14 Roundup, chemical resistant garden sprayer from Lowes. Application should be quick and easy.... no other treatments/ paints, etc. I think I can do BOTH sides with 2 gallons. Also, since it should penetrate through my 1/2" ply, any holes I drill will already be sealed.

Awfully tempting... and I pretty certain its the way I'm going to go. Havent seen anyone else in the AForums speak of it, so interested to see if anyone has any experience with it.

I'll be watching!
Mic

Again, a cheap and easy method to prevent rot has been the quest of wooden boat builders since Noah. Epoxy is the best, most expensive and most laborious way. It has a proven track record with now 40 year old boats. Lesser methods will have lesser results. What level of protection is good enough for you? Only you can answer. Probably the original floor had no rot protection at all and was thought "good enough" by the airstream factory.

If you want epoxy get real coating epoxy meant for boat building. Its better and cheaper than the general consumer products like Rot Doctor. You want 100% solids epoxy, zero solvents, which means it is pretty thick at 70 F, thinner than honey but thicker than olive oil. Things meant to penetrate rot are usually much thinner so they soak into the wood and are made thinner by mixing in solvents. The best product if you want to paint on thin epoxy is Smiths Clear Penetrating Epoxy Sealer. Used as primer by many boat builders; smells awful, I'd only use it outside on a windy day.

BTW: Nothing penetrates the flat grain of wood more than several .001". the end grain will suck it up maybe a 1/4" or a 1/2". Advertising claims that say "penetrating" never say how deep.

[HiHoAgRV]

I went the same direction as McDenny talks about, using a good grade of plywood and coating with RAKA epoxy. 3 gallons were more than enough and cost less than a local sheet of marine grade ply.

[AtlasCoffee]

Originally Posted by HiHoAgRV

I went the same direction as McDenny talks about, using a good grade of plywood and coating with RAKA epoxy. 3 gallons were more than enough and cost less than a local sheet of marine grade ply.

I think I'm going this route too. Frame repair is this week so I have a few days to make a decision.

Thanks everyone for your input!

[Jewel65]

For the coating I am using an oil base floor paint from Lowes at about $16/gal. It is called All Purpose Floor and Utility Paint. I used it on the wooden floor of my shed and it has held up well, so I am using it on the airstream. It is about the same gray color as Trempro and the oil base penetrates the wood grain well. I am painting all sides and the edges with 2 or more coats. I think it will last well.

[barts]

We used regular 3/4" A/C construction plywood when patching our floor, and covered the old and new plywood with epoxyproducts.com "no blush" epoxy (3 coats IIRC). The first coat was thinned 10% w/ xylene to sink better into the water affected (but not completely rotted) areas.

We painted the epoxy with Aluthane, a moisture cure aluminum filled polyurethane paint by the same folks. This has worked very well, and we just use rugs over this. Note that this lets us find any leaks or other issues very easily.

- Bart

[Silverflames]

When we replaced the back 4 feet of our AS we used marine Grade 3/4 ply. It was about $75k, and we top coated it with fiberglass resin. We fully coverred the top, and then coated about 1 foot around edges on the bottom. The rest of the floor we primed with oil killiz and toped with a oil based floor paint. It came out pretty nice. I walked on it to soon, so there is a few off spots. I we have a floating floor to go on top, so not a big deal. The goal was to seal it up as well as possible.

[perryg114]

Where do you get real marine plywood?

Perry

Originally Posted by Mcdenny

Hi, just joined the forum, been lurking for awhile.

I'm a wooden boat builder and have used a lot of plywood. Most all plywood has water proof glue. "Marine" plywood just refers to a higher manufacturing standard usually, few or no voids in the interior plies and equal thickness plies. Lesser ply will have paper thin face plies. Doug fir is heavy, strong, moderately durable and miserable splintery stuff to work with. I never use it in boats. Better options are Meranti or Okoume plywood. Meranti is 25% heavier than Okoume, more durable and half the price. Okoume is mostly used where strength and light weight is wanted, like a kayak. Both woods look like mahogany. Meranti is sold under the trade names Hydrotech and Aquatech. Either would be good for the floor.


Meranti is a bit lighter than DF and about the same price.


All the wood will eventually rot if not protected from moisture. Modern wooden boats (since the 1970s) have all the pieces coated with two or three applications of epoxy. (I get mine on line from RAKA).


If I were doing all that work, I'd use Meranti, cut all the pieces to their finished shapes, then put two coats on each side while coating the edges each time so the edges end up with four coats. If you later cut holes in the floor put a couple of coats on epoxy on the newly exposed wood.


Also note that plywood isn't usually exactly the thickness it's sold as. American ply is often 1/32 or 1/16 thinner than its 'size'. 1/2" ply is usually really 15/32". Exotic specie like Meranti or Okoume are made to metric dimensions but often sold as an inch dimension. There what is called 1/2" is really 12 mm. Don't know if this matters in a floor replacement.

Atlas, I see you are in the Detroit area. Public Lumber at Seven Mile and I75 carries Hydrotech. You can get WEST brand epoxy at West Marine at Nine and Jefferson. It's good stuff but 2x the RAKA price. It's all pretty much the same stuff in the jug.

[Mixter]

Google plywood or lumber supply. Got mine a intercitylumber.com - I think you can take a look at their prices online for your comparison... Marine Tech was the manufacturer of mine- you may be able to find a local distributor from their website. There may be a higher quality for "real" boat building, but I think the diff between the stuff I used and exterior grade is just less knots, gaps/ voids and a nicer top veneer. I think the glue is the same. True "Marine" ply for boat building is probably a better species for water...

[Mcdenny]

Originally Posted by perryg114

Where do you get real marine plywood?

Perry

Ask your local lumber yard if they can order "Hydrotech" or "Aquatech" plywood. It's the most widely distributed brand of marine plywood.


Boulder plywood in MA or Noah's in Buffalo, NY will ship small qtys.


If those are too expensive, I'd get AC fir (every lumber yard has this) and coat it with epoxy, paying particular care to the edges.

[Aerowood]

I went pretty much the same way, Just used standard ACX but I just mixed all of my left over cans of Poly together and coated both sides and edges multiple times. I really didn't dwell on this because I made it a quest of mine to stop the leaks. I can truly say that my GT does not leak, but it took some time to get there. During the process the floors in our hanger at work were being re-epoxied. I was able to get my hands on a couple of gallons of this cement penetrating coating which I rolled on 4 extremely wet coats on my floor, sanding in between coats. The color is white but the first 2 coats soaked in so fast that it was hard to tell that I had even applied it. The final coat was just a surface coat as the floor would not absorb any more. Most likely overkill but but it was free and easy to apply.

I think the most important thing is to stop the water from getting on the wood floors to begin with. If Airstream would have just sealed everything properly with a faying surface seal and throwing away the foam gaskets then we would not be dealing with rotted floors to begin with.