Roof redux: Fixing T1N seam rust

[InterBlog]

There is an existing thread on this topic but I decided not to build on it because it's 3 years old, and it contains a lot of "this is what I would do" rather than carefully researched, objective information that contains specifics. That plus the other thread's OP apparently never became a forum contributor.

Issue in a nutshell: Older Interstates were built on T1N Sprinters that had allegedly poor paint jobs on their roofs. The roofs are constructed of sheet metal sections that overlap, and are spot-welded over, the underlying structural ribs. The seams are vulnerable to rust.

I suspect that most, if not all, of the T1N Sprinters used to create Airstream Interstates had the same roof construction - someone please clarify if they find this not to be the case.

However, here's a complexity: Not all Sprinters have the same roofs. There is anecdotal evidence on other forums that only a subset of those that were shipped to the U.S. during a certain period of time have the roofs in question. So some paint / rust-related threads on other forums are dealing with unrelated predicaments.

Have any of you usual suspects dealt with this issue yet? If so, what approach did you use?

I'm early in my research but I thought I'd throw that question out there in the initial stages.

The ancillary question for me is that, after 10 years of life, the ENTIRE roof is not in optimal shape. The paint was thin to start with, and it's clearly oxidizing now. It can't hold a good wax job as a result (God knows I've repeatedly tried to apply one) and so it tends to build up dirt rather than shedding it, which is not good. So I ask myself... if I have to get up there to fix those seams, do I want to re-coat the entire roof in the process?

Some of the Airstream trailer people have coated their roofs with this or that product, and they swear that it improves heat rejection and makes their trailers easier to cool. A Sprinter roof is different from an Airstream trailer roof, but I'm wondering if this aspect is worth pursuing.

Here is a pic of the seam shown in the other Air Forums thread:

[LB_3]

My recomendation is to quit crawling on the roof. :-P

[InterBlog]

Sighhh... my husband LB_3 is currently on backshift and occasionally gets punch-drunk tired. Not to get the thread off topic before it even gets underway, but this is the backshift to which I refer (he's in this pic).

[don000]

Rust along the seam like that is a nasty problem. Ideally the affected area should be cut out and new sheet metal welded in. If you don't somehow deal with the rust it will continue, degrading the structural integrity of the assembly. You can't just apply a coating over it.

In your shoes I would use the POR-15 system to clean, prep and treat the rust, then add a compatible topcoat in your choice of color. It's a proven system.

Does steel rust in space ?

[LB_3]

Originally Posted by don000

In your shoes I would use the POR-15 system to clean, prep and treat the rust, then add a compatible topcoat in your choice of color. It's a proven system.

Does steel rust in space ?

I've was leaning towards POR-15 as well. I'm familiar with it from working on old rusted hunks of metal that serve no purpose but to make noise and go fast. As you noted, overlapping seams can be problematic since you can't access the rust under the seam like you could a butt weld. The goal is to hold off the cancer for another 10 years. At that point we'll have to decide wether to start building a new van or dropping $25k on body work and a new paint job.

As for space rust, Mars is red because of all the iron oxide. Closer to home, humidity inside the space station can be a source of corrosion. The few large steel assemblies get inspected and lubricated at various intervals wether they need it or not. Outside the station, atomic oxygen can react with lots of stuff but that's more on the time scale of decades.

[InterBlog]

So far I've gone through every Sprinter Forum post on T1N rust issues, which is a fair number of threads because the problems are extensive. I distilled bulleted notes on all of the different product recommendations and approaches for the seam rust issue. I'll have more to say about POR-15 after I get done digesting as well as other themes that emerge from that collection of threads.

Here is one thing that fell out of the analysis immediately: Once seam rust takes hold, if not addressed, it will quickly penetrate all the way through to where you're gazing at the stars from the inside if your Sprinter is an unlined cargo van, or you're having water penetration issues if it's a finished vehicle and the underside of the roof is hidden from you (such as with an Interstate). On Sprinter Forum, many T1N people aren't taking about sanding down rusty seams. They are talking about *patching holes*. So if you are a T1N Interstate owner, bite the bullet and get up on top of your rig to examine every seam closely. And for that I recommend a Telesteps 1400 E ladder and some segments closed-cell pipe insulation to slit open lengthwise to wrap around the portions of it that contact the side of the Interstate as it's leaning up against.

My question is really two-fold, though, because there's the seam issue but then there's the issue of potentially re-coating the whole roof at the same time as the seams are fixed. To address the second issue, I launched this thread on Sprinter Forums to ask for any updates people may have. Many of the seam threads are years old and the roof re-coating threads are far fewer.

More summaries to follow.

[don000]

State of the art for roof coating seems to be embedding polyester fabric in proprietary elastomerics to create a flexible membrane, with a high reflectivity top coat.

Examples from a quick search: http://accentstripes.com/RV_Roof_Coating.html, http://www.tdhalbrook.com/rv-roof-coating-systems

[InterBlog]

One of the things I'm researching is whether any of the RV roof solutions would be the best choice for something that is better described as a motor vehicle. Many trailers and RVs have wood-framed roofs with some kind of fiberglass or membrane construction, or rubber roofs, etc. Those substrates behave differently than automotive sheet metal.

[fencegod]

Fluid Film is an excellent product. It soaks into seams and stops rust.You will have to recoat occationally. I use it in New England for undercoating vehicle frames and body. it won't hurt paint, electrical etc. you can find it on the net.

[InterBlog]

Thanks. I have a few more sources to canvass before writing up the bulk of this research in a summarized form.

One of my neighbors stopped by yesterday; he does high-end automotive painting for a living, and he had some procedural ideas for me, including a specific local vendor.

I'm also going to speak with one of my yacht refurbishment consulting clients to see how they might approach this issue if it were occurring on one of their clients' boats instead of our van.

There are thematic consistencies emerging from all of these lines of inquiry, but a surprising diversity in the actual technical approaches advocated by the different sources.

[InterBlog]

Facepalm - why is there no Air Forums smilie for facepalm?!

A user on Sprinter Forum put forth a promising top coat suggestion called Bus Kote that made me do a facepalm because I've seen these very roofs on buses and yet I never put two and two together and considered the same treatment for a Sprinter. But of course it's a similar scenario - big ribbed sheet metal motor vehicle roof. A bus is a bus.

The user claims about 40% interior heat gain reduction because that's what the product was specifically designed to do - reject heat without adding much weight. Here's his Insta depiction of his own roof and yes, he also had the rust issue before he tackled his roof reno:

https://www.instagram.com/p/BGszuwopQlb/

[don000]

Bus Kote is essentially just the topcoat of the systems I mentioned.

There's a good chance that the rust occurring at your seams is an indication that the panels are moving slightly in relation to each other.

The Bus Kote application instructions mention spot patching with polyester tape, but you would probably have far greater durability with an all-over fabric embedded in elastomer.

[InterBlog]

First stage of this project is now complete, using POR-15 metal prep followed by POR-15 coating (paint) on the seams. Blog post with instructions on this particular approach:

REFINISHING AN AIRSTREAM INTERSTATE'S ROOF, PART 1: SEAMS

[InterBlog]

An update on this two-part project...

This morning I ordered my products from Hy-Tech Thermal Solutions so that I could put the heat-rejecting coating on our roof.

I was inspired to get off high center on this project because after spending a night right on the beach last week, I washed the van and climbed up on the roof to clean the seabird poop off the solar panels. It was early in the day and was only 80 degrees and partly cloudy, but the roof was already so hot that it fried my butt. It was too hot to sit up there. And I sez to myself, "I have to try this thermal coating; this roof must be adding one heck of a lot of heat load to the van even with the solar panel shading."

One thing I'll say about the Bolivar Ferry is that it gave me the opportunity to get the best roof photos I've ever taken. I'll be adding the Bus Kote to the darker gray area that you see here in this photo below. The lighter gray represents the automotive painted areas added by Airstream. The darker gray in the center of the roof is the old Sprinter primer coating.



You can see the POR-15 treatment that I added to the roof lap welds more than 2 months ago. It turned a bit brownish green in the intervening time but it's totally intact and feels as hard as ceramic. It'll be covered up by the Bus Kote.

ADVICE TO ANYONE CONSIDERING THIS MOD: Call Trish at Hy-Tech and walk through your scenario, because what's on their website is not in the form of individualized suggestions. Hy-Tech is located in coastal Florida, very similar environment to Galveston County where we live, and what she told me to do product-wise was different from what their website suggests. When salespeople start using words like "viscosity" and "adherence", it's encouraging. We spent close to 30 minutes on the phone talking about what would be best for my van now and in the future, and all that on a sale that only ended up amounting to about $150.

Anyway I'll post back on how this endeavor proceeds.

[73shark]

Originally Posted by InterBlog

The darker gray in the center of the roof is the old Sprinter primer coating.

If the darker gray is truly only factory primer, then it's no wonder that the seams rusted. I'm surprised that's all that rusted as primer provides no protection from the elements.

[InterBlog]

It looks like a duck and quacks like a duck but it might not be one of the usual species. It's an ordinary flat gray paint, and it has the visual appearance of a primer. It was only when I ground down the roof seams for treatment that I discovered that there are actually three thin layers - one white, one tan, and the top one gray. I don't know what that signifies.

Whatever it is, it's thin and doesn't look like typical automotive paint. Part of what I discussed with Hy-Tech was, what's the best surface prep procedure for this stuff, given that it's not the usual?

On Sprinter Forum, it is speculated that Sprinter lap welded seams rust in part because the paint is crummy but also because the van flexes as it moves, opening up tiny gaps between the spot welds. The flexure hypothesis may be supported by observation; every time I angle-back into my driveway, raising one wheel at a time, I hear metal creaking all over the van.

[Lotus54]

Mine is white on top- looks like factory MB paint to me.
It is easy to see where airstream painted it (no rust at all on this, might have been stored inside)

[InterBlog]

Keep an eye on it. We had no roof rust 2.5 years ago when we first purchased ours. And of course we do keep ours in a garage most of the time.

Once it started, I was amazed at how fast it progressed. And as I probably mentioned earlier, there are stories on Sprinter Forum about people seeing daylight through their roofs, due to rust-through.

[Lotus54]

I will most certainly keep an eye on it. Especially since I have it outside.

BTW, there are primers that can act like a sealant- epoxy or catalyzed ones are reported to seal to weather.
Iv'e used those before, especially when painting fibreglass cars. (Lotus and old SAAB)

[InterBlog]

Time passes quickly and details become fuzzy in the mind. One thing I've found that helps generally is to cover the Interstate with photographs even if I think I won't need them. They allow me to gauge the progression of any issue in a way that I could not from memory alone. They allow retrospective inspections.

Example... February 7, 2016 - Superbowl 50 - just happened to have been the same day we finally got our solar panels on the roof. We took a short break to watch the half-time show.

Well, naturally I have photos from that day showing the condition of the roof (blog post). There was NO rust on our aft lap welded seam. Zippo. Furthermore, our sealant still appeared to retain 100% integrity. Like brand new. Virgin condition.

Fast forward less than a year later, and the caulk is shot - it needs to be replaced immediately. And the seam is showing incipient rust (blog post).

I don't know what the hell happened. It's not like we subjected it to any harsh conditions in the intervening 9 months - most of that time was spent tucked away in its garage. This is just the way things went. But without the historical record of photos, I wouldn't be able to gauge the velocity of the processes, and thus the urgency of the need to intervene would not have been as obvious to me.