u-channel repair: shell-on floor replacement

[60traveler]

we are doing a total floor replacement, shell-on, on our 1960 18' traveler. we have made our chassis repairs and painted with POR-15, so that it's all nice and pretty...now we're going to cover it up with a floor...FINALLY!

our question is this: we have about 4' of floor channel (u-channel? c-channel?) that is badly corroded, located in front of the wheel well, streetside. the 3" directly in front of the wheel well is...well...kinda completely gone. our thought is to have a local sheet metal shop make a replacement channel of sorts: similar gauge, but just slightly smaller so that we can nest the new channel into the old to reinforce it. we think we can pry up the banana wrap around the outer edge...ever so slightly...just enough so that we can tuck the new channel in there...then fold it back over. then we fasten it all together with pan screws once the new subfloor is installed.

will this work? we would love any feedback.

we've been on a hiatus for a year or so...but we're back on task and are really glad to be working on our gal again.

i'll try to post a picture of the area in question.

martha and stacia

[HamiBambi]

Hey Martha and Stacia,

I'm not exactly an expert at this but since nobody's responded I'll tell you what I know and I'm interested to hear if anyone else weighs in.

I've been told that it's fairly easy to find and replace straight sections of u-channel and there's no doubt getting a metal smith to bend a piece up for you would be a piece of cake. The curved sections I'm told are hard to find but I'd be curious if a metalworker could make those too and I'd love it if you'd ask the person just to see cause I'd be interested in hearing if there's more to this than meets the eye because to me it seems like it wouldn't be rocket science. I mean, somebody made them in the first place right?

I've never gotten a clear explanation of exactly which metal is what everybody refers to as banana wrap but if it's the belly pan as it folds up and over the edge of the u-channel then I just had some experience peeling off all of that stuff on my '62 Bambi that I'm doing a shell off for. These are the questions that I'd ask.

1. If you're going to slip the u-channel inside (which sounds like a clever way of handling it) then maybe you don't even need to peel back the belly pan (banana wrap) maybe you could just slip it inside the belly wrap too and screw it down.

2. That said, I wonder if putting fresh metal next to badly corroded metal might just quickly infect the fresh metal too.

3. And do you know, and have you solved, the source of the corrosion in the first place. ie. Was there a leak or something and does that need to be addressed. My U-channel was badly corroded in the front where there was a leak from a replaced front window, and along one side where the PO had put in a really stupid and badly installed hatch that leaked like a sieve. Everywhere that there were no leaks the stuff looked shiny and like new. (Isn't aluminum amazing?)

Honestly, I'd say if you're going to the trouble that it would be preferable to remove the corroded u-channel and replace it. That peeling back the banana wrap and then re-folding it over the edge of the new stuff should work, but I did find that the black tarry stuff that they slathered all over it originally tends to chip and break off when you bend it back and so the seal there will probably be compromised and I would re-seal it. (I'd asked on my thread "is this plan totally crazy" if anyone could tell me if the black stuff is what they call vulkem or if it's just some sort of tar but nobody's responded to that one yet. It was used liberally all over my trailer. Anyway, I'd be sure and reseal it with either Vulkem if somebody thinks that's appropriate or with that black tarry stuff if somebody would please explain to us what that is!

Hope those thoughts and questions are helpful and congratulations on your new floor!

Best!

Steve H.

[1959newbie]

Dear Martha and Stacia,

I just finished piecing in the new sub-floor "shell-on" in my 1959 Overlander!!!

It took 16 solid hours of work, alongside a skilled carpenter who was convinced that everything I asked him to do was impossible -- if I hadn't been totally convinced that it WAS possible (and if I weren't really bossy), he'd have given up after the first two hours, when we still hadn't even come close to getting the curve right in front. But every piece after that first one went smoother, we wound up getting every section in full-width, and only used 6 sheets of plywood for the 23' long floor!

I have the same problem as you, with some corroded-out sections of channel. I think that Steve is right about the importance of fixing any leaks. But the corrosion is not "contagious," it's the result of dissimilar metals touching while wet. So aluminum touching aluminum is OK, it's the non-aluminum fasteners touching both that are the issue. From what I've read on NASA's website, if we can't find aluminum fasteners, zinc-coated may be a good choice.

The problem with our "shell-on" replacements and new channel is that totally replacing the channel requires the very thing we are trying to avoid: drilling out and replacing the bottom rivet line! (Although once the floor is in, it would be possible to do that section by section, without having to completely remove the shell and re-fit it.)

I am in the middle of trying to decide what to do about the problem you raise. One solution would be L-shaped strips of alclad, which could fit against inner edge and bottom of original channel, be riveted to inner edge and screwed or bolted through bottom of old channel, new subfloor, outriggers where they occur. As long as significant portions of the old channel are intact, it seems to me that this could make a solid attachment.

I'll be interested to hear what others have to say. Good luck, and feel free to ask me anything about getting that floor back in -- quick, before I forget!

Here are some pics of the sub-floor going in. We did the front 4' section first, then the 4' section that spanned across doorway outriggers, then the 4' piece aft of that (halfway around wheel-wells), it took 12 hrs. Next day, in 4 hrs, we did rear 4' section, other 4' piece around wheel-wells, 2' strip between that and rear piece, and finally 2' strip just behind front piece. We obviously got better as we went along! Actually, the front curved piece was the only one that required many,many ins & outs & trimming.

[60traveler]

steve and lynne,

thanks so much for your input on this.

lynne, congrats on a fantastic floor! it looks great. the floor is our next step and we're trying to figure out how to do it in as few pieces as possible. the old floor came out in many pieces, but we managed to save most of the perimeter to use as a template. we're trying cardboard first as a dry-run; we'll see how it goes. our challenge is that we don't have much wiggle room behind the wheel wells (it's an 18 footer). i guess we'll start with as few pieces as possible and go from there.

back to the u-channel: the area in question was behind the hot water tank and galley kitchen. i'm pretty certain that the cause of the corrosion to begin with was leaky pipes. could also be a leak around the streetside window. either way, we'll fix the source of the problem.

glad to know the corrosion isn't 'contagious'. as lynne points out, completely replacing the channel would require drilling out that bottom rivet line on the outside. we would rather not do that...lest we be knocking on the door of a 'shell-off' project. if we can reinforce the existing channel, we would rather go that route.

i think (please correct me if i'm wrong) that the bottom of the inner skins are riveted to the inner vertical edge of the channel. so, if we nested a new channel into the old, we could (1) fasten the bottom of the channel by screwing into the new subfloor and (2) fasten the inner edge by rivets when we re-attach the inner skins. will that work?

the only thing i'm not sure about is that outer vertical edge. do we try to tuck it up there under the banana wrap (we have a lot of the black tar, too, steve...and i'll be curious if ours is as brittle as you experienced) or just do the L-shape and leave it at that? do you think that this would be solid enough?

martha

[HamiBambi]

If I remember correctly (and just to remind myself I went and looked at the most excellent diagram created by Nor Cal bambi that you can find in my thread about the Bambi shell off "is this plan totally crazy") the rivets around the lower perimeter of the shell that you're trying to avoid removing in fact go through both layers of the banana wrap. Thus I don't think you can peel it back without first drilling out those rivets tar or no tar. Consequently I think you may be stuck with the "L" channel version of your plan and by leaving the tar and seal intact you may be better off anyway. In my decidedly unexpert opinion, since you're only doing a small section this way, I think the method you've described should be adequate, and once the interior walls go on and are riveted to the c/l channel sandwich you'll have improved the integrity somewhat by creating a strong bond and joint with the interior wall to the u-channel even though the exterior bond is not improved. That said I'm sure many on the forums would point out that the strongest integrity results when all elements of the structure of the Airstream are working together and that one weak area makes the whole thing weaker. Unless someone on the forum more knowledgeable comes through with other options it's the only option I can see that would prevent you from having to remove those rivets.

Let's cross our fingers and see what the others have to say!

[AlumaBorg]

Thanks for these posts folks. I'm doing the floor of my 1960 Bambi right now and seeing it happen makes it way easier...

[57BB]

Martha and Stacia.

I had to chime in on this. I think in all worlds you will be much better off to get rid of the corroded channel, use what is left of it to have a new one bent. The key will be finding a shop that can bend aluminum stock. I found luckily on my recent floor replacement project...see 1964 Overlander section, that the channel was in pretty good shape. However, the dissimilar metals of the original screws and aluminum combined with leaking end caps, windows and a good amount of mouse pee caused a fair amount of corrosion.

Though I choose to replace the belly pan on my project I could see after having done the work how I could replace the front and back pieces of plywood without taking the shell off. I didn't take my shell of, but did remove the front and rear channels...we were probably 30 screws short of a full shell off renovation LOL. Getting the new plywood in, once it was cut using a template of the floor made BEFORE taking the old out was a breeze. It took no more than 10 minutes to get it back into place.

Something not mentioned in the other posts are the steel angles that attach the first vertical body channel to the front and back channels you are discussing. Those angles are critically important to the structure and you should inspect the condition of these...replace them if they are non existent or are badly damaged.

Taking the bottom line of rivets is not as awful as it might seem. I'd advise just taking them out as far back as necessary to allow you to peel down the belly pan and banana wraps and take out the channel. Once you get the new plywood in place it will be quite easy to reattach everything. Then at the end of it all you'll have a very sound structure that you will not have to worry about having future failure or problems with.

I agree with HamiBambi...every single rivet is an important element of the Airstream and once one fails then others fail and as the failures increase then larger parts of the system fail...so I'd always say as much as possible stick to the original design and don't reengineer anything. The same philosophy does not apply to water systems or electrical however...just to the structure and skins.

The black sticky stuff is not Vulkem btw. It is an interior joint sealant god knows what that stuff is made of, I always fear asbestos in black tar substances from that era so I'd suggest handling it with care and don't bother removing it. I would however suggest that you look at the exterior seams, particularly in the end caps. Once Airstream stopped crimping the edges of the end cap sheets in 1957 (at the end of the 13 panel era) and changed the panel design to a flat edge panel the end caps always leaked! The earlier era crimped or rounded edge acted as a water stop, it kept water from traveling against gravity and up the back side of the panel. As soon as the stop was removed the only thing that kept water from making its way between the panels was the tightness of the rivet joint and this black gunk. The black tar junk was an attempt to stop water from having a way in. The only problem is the gunk drys out after 50-60 years and loses its flexibility and ability to prevent water from getting through. On the vertical seams and the horizontal seams where you also find this stuff and at these locations there is a fabric or shredded fabric blended into the mix...I'm almost certain the fibers are toxic as well. If you can leave that in place do so and just seal up against it. On my 64 I picked every seam on the exterior...yes every one of them as deep as I could get the picks in and then used Acryl-R (sold by Airstream) to seal the outside seams. This stuff is far far better than any other sealant out there. Then I actually used a couple of products by 3M to seal the seams on the interior. I used a panel sealer for auto body construction to seal around all of the windows, door and hatches. I also used the panel sealer over the seams of the end caps. Once that cured (over night) I then sprayed a flexible seam sealer by 3M (similar to Flex Seal) over all of the interior seams. Both products are available from any auto paint supply shop. I went from having dozens of leaks to having zero leaks. The two 3M products can be applied right over the original sealing material and will last for decades in the dark environment of the interior wall space of the trailer.

For the new screws to attach the new channel to the new floor use a zinc plated screw (with a metal/rubber washer) or even stainless hex head screws...both will last for many decades and both (though Stainless will hold up better) will resist the inevitable leaks that will occur.

Last word, all Airstreams leak...its just a fact of life. Like the structure of the trailer the water resisting elements have to be maintained. I recommend that you review the exterior seams once and year and with your trusty Acryl-R you will be able to fight off the most corrosive element on earth....Water!

Good Luck!!!