Plywood floor alternatives - engineering opinion

[perryg114]

The drains are just a stainless tube with a flare at one end and then that end is sealed with Parbond. The tube goes through the C-channel and floor to funnel water away from the floor. The newer trailers have weep holes on the outside of the bottom channel that cradels the floor. If you put in weep holes in the same location on older trailers the water would just soak the end grain of the plywood and you would still have floor rot.

Perry

Originally Posted by rippie

Perry
How did you go about placing drains in the c channel?

[rivet-rivet]

Joined the forum yesterday. Considering purchasing an Airstream because of looks, less drag while towing, and needing a larger TT. Reading threads about possible future maintenance issues. Floor issues are a concern for us.

Currently own an aluminum 2010 LivinLite CampLite 11RD "basic" 1500lb TT. We call it our aluminum tent with heating & cooling. LivinLite is owned by THOR Industries, too.

Before purchasing the CampLite, our previous 2004 Chalet A-Frame camper had floor rot. After 2004, Chalet changed to a "composite" floor. Called them and they said the new floor contained marine plywood to prevent future rot.

One of the reasons we purchased the CampLite was the aluminum plank tongue & groove type floor. It should be more durable than wood, but also has negative issues when compared to wood. It's not insulated and when towing in heavy rain, water will sometimes seep up between the planks. We roll up the carpet while towing. One guy I met with a LivinLite toy hauler with aluminum plank floors said when he unloads his ATV vehicles, he washes the floor out with a water hose.

Since this thread is about plywood floor alternatives, here's a couple shots of the CampLite aluminum floor with aluminum frame, without wood.

View from underneath the camper:



View standing on the floor:

[Belegedhel]

Originally Posted by rippie

This is a very intimidating discussion. I do not have anywhere near the engineering qualifications to suggest structural change. In fact, now that I can see and manipulate the exposed frame and have to replace some crossmembers, I have already changed my repair game plan due to fears I might add too much weight and reduce flexibility to the unit. This steel seems to have interesting properties, strong, yet lightweight while being flexible (mine is stamped "Roswell, NM 1947" & has some strange sort of alien characters on it, Ha! )

But here is a weatherproofing suggestion: Has the idea of an aluminum flashing been discussed between the outer skin and the C- channel/plywood? It could be bent to follow the outside contour right below the trim (at least that would seem to help with my '72). Perhaps it could act as a mini external gutter to follow below the trim, effectively incorporating with it in appearance. It would be sacrificial and sparing of the skin at the end plates. This could obviously affect aesthetics, but once I get down below the trim, I am thinking more about weather proofing than looks. But I am sure there are different ways of possibly incorporating it into the belly, also. In theory, I picture it as the inner lip that you have on a cookie tin. I don't know if it is original factory construction or not, but my belly skin overlaps the outer skin (under the trim). The inner skins are also the same in the bathroom/shower (although, I give the PO credit for incorrect reassembly here. But it seems that if your seams overlap in an underbite, you are inviting water seepage.

If you have a cookie tin and sprayed water on it, you would have some structural protection. But if you turn it upside down, the structure invites seepage. *NASA if you are reading this, please note I have had no formal training* Getting to the point... flashing may provide the inner "cookie tin" lip structural advantage without changing the time-honored c channel/plywood sacred cow. But it is possible that all of what I am seeing and basing my suggestions on are PO reassembly error. My rear bumper box and its union with the body I feel is, by far, the reason for my floor rot. The box flooring was continuous with the belly pan which made the belly pan a nice little drainage pool. The top of the box behind the hinge went below the outer skin and under the c channel, making the plywood flooring a nice little collecting pool as well, with nice little eventual waterfalls to the pools down below. I can't imagine this was factory construction. What was original? I think this box would be better of completely separate from everything else.

If anyone is still reading this, and in the interest of moving closer to initial thread topic, I am interested in ideas on pros/cons of plywood & all the potential treatment methods and any non-plywood alternatives. Some current thoughts: Coosa bluewater 20 (?), HD or LD (?) polyethylene sheet (kitchen cutting board material), Plywood with (1)water stain 2)epoxy primer/paint 3)fiberglass layer 4)linoleum or shower wall material (?) sheet covering 5)just plain Marine. But to me, more importantly, is what to do at the exposed ply ends: coatings, bumpers, or what?

Now...fire away!

The idea of using an "L" shaped flashing to keep water out of the rear of the 70's era trailers has become something of a "best practice," and is discussed in various threads. I installed one on my trailer during the rebuild of the rear area, and so far, so good.

On this topic, I did make some mods to the rear of my trailer, in that I installed the steel angled bracket on top of the plywood, shortened the plywood, and put a 3/4" steel square piece that is welded to the angled bracket. The purpose behind this was to make the plywood less critical to keeping the rear of the shell in contact with the rear of the frame. My rear-most cross member was replaced in the rebuild of my frame, and is a little wider than the stock piece to allow all of this. As for the rest of the floor, I replaced it all with 3/4" marine grade plywood with 3 or more layers of spar poly. I figured if the old untreated, non marine grade stuff lasted somewhere in the vicinity of 40 years, then this would be overkill. Were I to do it again, I probably wouldn't go with the marine grade plywood and just use construction grade plywood.

It is easy to go crazy with a complete redesign of some aspect of my trailer; however, then I look at the world of marginal design and construction in the rest of the trailer. I realize that if I keep it up, I will never get it back together, so I need to find some happy compromise and get on with business.

[nickcrowhurst]

My experience of "marine" plywood, to BSS 1088 specification is that it will rot within just a few years if it is subject to fresh water, as in rain water or plumbing leaks. The "marine" specification relates to the "water and boil-proof" nature of the glue, and the number of voids permitted in the internal layers of the plywood. It does not specify the rot-resistance of the timber.
I built an ocean-going yacht in the early 70s from thirty two sheets of half inch marine plywood to BSS1088 specification. The hull below the water-line is still perfect, after 40 years in sea water. Anywhere above that, where subject to rainwater, has suffered rot problems during the past 30 years. The decks are of marine ply, covered with woven glass cloth and epoxy resin. These are perfect after 40 years. Anywhere that a joint opens up, allowing rainwater in, causes serious and extensive rot. Most marine plywood yachts from that era have been scrapped because of freshwater rot.
Sea water acts as a disinfectant and preservative on timber.
Nick.

[Tim A.]

Nick has it right with regard to marine plywood. Only the glue is "waterproof." The resistance of the wood in the plies to rot is an entirely different matter. Wood rot is caused by fungus. Woods like teak and redwood are resistant to fungus, but are expensive. Fungus requires moisture and, as Nick has pointed out, moisture without salt in it. For real rot, that moisture needs to remain in the wood long enough for the fungus to grow. Even so-called "dry rot" requires some moisture in wood.

Should Airstreams use wood in the floor? That is an entirely different question. Wood and plywood, when kept dry, are wonderful structural materials. For example, many of us live in houses constructed mostly of wood.

The belly pan of an Airstream is useful for holding insulation and such, but it also can hold in water. Rather than trying to make it watertight, I have drilled 1/8" holes in the low spots in the belly pan of our Airstream to drain out the water which inevitably gets in there.

Tim

[Uppie89]

Very interesting topic. I've posted about it myself a month or so ago. I will be beginning a complete tear down and restoration of my 1970 ambassador this spring. This topic in particular I've researched, read, looked at pics, researched some more and think I have finally figured out my plan of attack. Please feel free to comment and give opinions. I have big shoulders LOL.

I have worked with a material called Starboard. Basically 3/4" 4x8 Sheets of Marine Grade polymer material. We have made outdoor cabinets out of it for High End Clients. I plan on using the std foil bubble looking insulation on the outer skin with your std foam board insulation on the top of that then the star board for the floor. Also adding weep holes on the "C" channel that drain to the belly pan with holes in it to drain on out.

In addition to this since i will be redoing the entire interior I plan to hold all the cabinets and wood work 3" tall x 6" back from the perimeter of the airstream. So even if it does leak it will run down the foil insulation into the c channel to the belly pan to the ground. If by chance water makes its way threw all of that and the interior skin, It will lay on the starboard and will have to roll 6" to touch the woodwork. Witch will all be plywood anyways.

So the only material that will be able to wick moisture will be interior millwork that's 3x6" away from the perimeter base. There will be a few areas that will touch for aesthetics. But by opening a cabinet door Ill be able to see the other side.

Thoughts,. Ideas, I'm a idiot!!!! LOL

[Wingeezer]

When I worked for Canadian National Railways (worked there for 34 years) way back in the mid sixties I was somewhat involved in the "Turbotrain" project. (Gas turbine trains designed by United Aircraft). They ran for some years in both the US and Canada.

I remember that they had aluminum honeycomb sandwich construction flooring - wonder if AS ever considered that type of material. I imagine it may be standard in aircraft.

Just a cost decision, or other problems?

Seems to me if people are willing to pay as much as they do for these trailers that are supposed to be top of the line, then they should be, and with the current flooring material think they fall short.

As I've said in other threads - well, maybe this one? - if they changed this I would be quite keen to buy a new AS, but as long as the current floor design is perpetuated, that is nor going to happen!

All trailers leak and the water finds its way to the floor!

Brian.

[Bill M.]

What else is there to use for a floor? I am sort at a loss to think what materials I have seen that would make a better floor than plywood?
What do they use in the European trailers? I have heard that the floor is 3" thick on the European model. That would hurt headroom a lot.
Most do it yourself replacements seem to be plywood. Many commercial truck floors are wood.

[Uppie89]

Check out the starboard. Just google it. I think it will be good to use. Maybe heavy though.

[JimGolden]

I'm an aerospace engineer too. I'm also building my original-design plane

I used to work at Boeing. They used to have Boeing Surplus. That place was a TREASURE TROVE for folks like us! They had the honeycomb flooring out there for cheap. Too bad the place closed up a few years ago. That stuff new would cost more than the rest of the trailer. But there, it was pennies on the dollar.

I'd designed a totally new frame for my 31' Excella. I was going to make it 8" deep. Get a much bigger "I" and all the SAG problems go off into the sunset. I also don't by the myth that these trailers are monocoque...the cutouts are too big.

Because I was building my house at the time, I didn't have time to build the hoist mechanisms to pull the shell, roll the old frame out, and roll the new one back in. So I sold the Excella and got an Avion 34X. The biggest difference between Avion and Airstream that I see....Avion's frame is much heavier and the shell sits on a perimeter frame attached to the outriggers and the floor sits inside. Sound familiar to some of the "better ideas" on this thread??

The one gent had what I consider an excellent notion: Do the perimeter plate and let the skin attach to that; have a 1/4" gap, and have your treated floor inside that. Gives the water a place to drip through without messing up the floor. Heck, use TREX or something for the floor if you can't get the aluminum honeycomb.

Another trick Avion did was that they put linoleum on the floor, wrapped it completely around the edges, and stapled it from the bottom. In other words, you cover the top surface, wrap around the edges, and have a 3" overlap on the underside. That way if/when water does get to the edges of the floor system (which is actually two sheets of 1/2" plywood with 1" staves between them....think I-beams, with foam insulation between the staves), it can't wick into the wood.

Don't get me wrong, I really liked my Excella (even with the dual pane Vista Vue's that leaked like a sieve and the Scotch Tint dissolved into crumblies that looked like somebody poured their smashed up frosted flakes into the space between the panes). If I wasn't in the house building mode, I'd have built a new frame.

Indeed, I'd still like to get two of them, cut off the front of one and the back of the other, and build a 40 footer with a couple of slides. Might do it one day.

But if you're going to this length, I like your idea of setting the skin on its own thing and putting the floor inside it.

We Eng-I-Neers tend to think logically alike....usually

Best of luck,

[73project]

Originally Posted by JimGolden

Another trick Avion did was that they put linoleum on the floor, wrapped it completely around the edges, and stapled it from the bottom. In other words, you cover the top surface, wrap around the edges, and have a 3" overlap on the underside.

In reading through this thread, I was thinking of something similar: What about self-adhesive window gasket tape? It's the 6" or so black rubber tape that you apply around the framing of window openings in houses before putting in the windows.

Would wrapping that around the permitter edge of the ply (so it wraps from the top, around the side, to the bottom) be a useful addition? Bonus is that it seems like it'd be a pretty simple and relatively cheap addition.

[EZEtwo]

I removed my complete floorsystem of my Excella 310 motorhome last winter. I worked my way down up to the aluminium sheet that covers the steel frame. In the meanwhile, I also replaced the aluminium sheets that were too far gone on some places. Have glued 3cm thick (1,18inch) (sorry, living in Europe = decimal system) PIR foam rigid board insulation on top of the aluminium. I used canned PUR Spray to glue it onto the aluminium and aslo to glue the plywood onto the insulation. I covered the whole with light weight poplar multiplex board with a thickness of 12mm.(0.47 inch). Using the PUR foam + self tapping metal screws. By this, I created a anti-condesing barrier between the cold metal/aluminium flooring and the poplar plywood. The combination of the PIR board insulation topped with the poplar plywood gives enough rigidty. I then have put on a 2.3mm vinyl floorcovering. Very easy to clean, just put an extra carpet under the table in cold periods.
Will post some pics. if you want. My floor is now about 1inch higher then before.

[rowdyATX]

I’m glad I read this post! Without a template to help me replace the subfloor in my ‘56 - 26 footer, I was able to get a piece of plywood in the nose of the trailer but after that, I spent a few hours scratching my head, struggling to find a way to measure the next piece, correctly. I’ll add, I’m trying to replace the sub without removing the belly pan or shell. So, after reading this post I’ve decided to use a hybrid method; insert full plywood in the nose and rear, fitted underneath the c channel, but for both sides I will insert 3/4”x2 1/2” square tubing or bar stock mentioned above, running the length of the trailer with 1/4” gap. Hopefully, this will allow the trailer to flex enough, and if ever need to replace any of the subfloor under the bathroom or kitchen or over wet areas, it’ll be easy(er). Thanks for sharing!