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Old 11-04-2017, 02:29 AM   #1
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Avoiding Corrosion and Filiform - Just Add Water?

Well, just finished the annual pre-winter washing and Walbernizing of the FaN. Last year I did not get either done. The poor thing (trailer, that is).

Sometimes I Boeshield the rivets, but that was neglected last year too. And the year before, if I remember correctly.

The FaN has also endured seven years of weather. Cold winters, hot summers, and a lot of rain here on the "wet coast."

So, after the wash, I did my usual skin inspection and was expecting some of those dreaded blemishes from corrosion and filiform.

But, there was nothing. Zilch. As you can see, the skin looks as good as the day I haulted the FaN off the lot.

Could my theory really be true? A trailer parked here on the wet coast means any airborne particulate doesn't have a chance to inflict cosmetic damage. (BTW, I also rinse the FaN once a week during the hot/dry spells).

This is just theory, of course. One based on experience and speculation, but if there really is any truth to this, thought I'd share.
(Pardon the bad photo -- all those reflections. The skin really is better than what the photo shows.)

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Old 11-04-2017, 04:45 AM   #2
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As a former engineer along the wet Gulf Coast, and having had formal training in corrosion prevention and removal courtesy of my former employer, I can safely say that your theory is not correct.

Filiform corrosion occurs on metal surfaces under a coating. Not just clear-coat, but also under paint, and not just aluminum, but any metal that can oxidize. It occurs when moisture is able to get under the coating. Any metal oxide molecule is larger than a metal molecure, so corrosion causes expansion. Expansion lifts the coating, which exposes more metal to moisture. This is what forms the characteristic "worm-trail" filiform corrosion. (The word "filiform" means "thread-like.")

Filiform corrosion typically occurs around rivet holes because Airstream purchases their aluminum sheets pre-coated. Then they punch rivet holes, but do not coat the cut edges of the holes. That provides a break in the coating where moisture can enter. Normally the rivets are tight enough to keep the edges of the clear-coat pressed down tightly so that moisture can't get under the clear coat. But if the rivets loosen up over the course of many miles on the road, then moisture can get in, and the corrosion starts. Any scratch in the clear-coat that penetrates all the way to the metal can also be a place for filiform corrosion to start.

If the whole clear-coat has been removed (as when Airstreamers evolve into Airstream-polishers), then filiform corrosion doesn't happen, because it can't happen without a coating that has a hole in it where moisture can enter and be trapped. If all of the rivets and the gaskets around the lights are tight on a clear-coated trailer, filiform doesn't happen because moisture can't get into the holes in the coating. If you apply another coating (Walbernizing, Boeshield) that prevents moisture from entering the holes, then filiform corrosion doesn't happen.

But washing the trailer to remove formerly airborne particles that settled on the trailer doesn't prevent filiform corrosion.
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Old 11-04-2017, 05:10 AM   #3
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If Airstream buys their sheets pre-coated that would explain the filiform that I've seen all along the edge of a panel on some of the newer ones.
They must have to trim an edge then there goes the coating.
Airstream was/is not doing anyone any favors by coating them.
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Old 11-04-2017, 08:38 AM   #4
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I firmly believe that there are periods of manufacturer coating issues. My 2007 has very little filiform on original panels. When I had 2 end CAP panels replaced in 2011, one of them started corroding randomly, in the center! Not on edges or rivets. Fortunately or unfortunately, these same two panels require replacement again due to an evil, rogue black oak.
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Old 11-04-2017, 12:52 PM   #5
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I believe Protagonist has it just right.

Our 2009 International is stored 100 miles inland of the ocean to avoid salt air, but not quite all the way into the SoCal desert. When we travel to salty areas (Corpus Christi and Sluth Padre border some of the saltiest water in the US) we always wash, dry and wax immediately after our stays.

I also periodically wax along the easily accessible rivet line as an additional precaution. In our eighth season, we have just seen the start of some minuscule corrosion in two or three spots along the edge of the panels below the rivet line.We’ve treated with corrosion x and are keeping an eye on it. Otherwise, we are corrosion free.

I believe that being careful around salt water/salty mist is imperative—I know this from coated aluminum on sailboats around salt water.. But I don’t think keeping yiur Airstream in a wet environment will protect it from filiform corrosion.
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Old 11-04-2017, 01:59 PM   #6
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Quote:
Originally Posted by Protagonist View Post
As a former engineer along the wet Gulf Coast, and having had formal training in corrosion prevention and removal courtesy of my former employer, I can safely say that your theory is not correct.

Filiform corrosion occurs on metal surfaces under a coating. Not just clear-coat, but also under paint, and not just aluminum, but any metal that can oxidize. It occurs when moisture is able to get under the coating. Any metal oxide molecule is larger than a metal molecure, so corrosion causes expansion. Expansion lifts the coating, which exposes more metal to moisture. This is what forms the characteristic "worm-trail" filiform corrosion. (The word "filiform" means "thread-like.")

Filiform corrosion typically occurs around rivet holes because Airstream purchases their aluminum sheets pre-coated. Then they punch rivet holes, but do not coat the cut edges of the holes. That provides a break in the coating where moisture can enter. Normally the rivets are tight enough to keep the edges of the clear-coat pressed down tightly so that moisture can't get under the clear coat. But if the rivets loosen up over the course of many miles on the road, then moisture can get in, and the corrosion starts. Any scratch in the clear-coat that penetrates all the way to the metal can also be a place for filiform corrosion to start.

If the whole clear-coat has been removed (as when Airstreamers evolve into Airstream-polishers), then filiform corrosion doesn't happen, because it can't happen without a coating that has a hole in it where moisture can enter and be trapped. If all of the rivets and the gaskets around the lights are tight on a clear-coated trailer, filiform doesn't happen because moisture can't get into the holes in the coating. If you apply another coating (Walbernizing, Boeshield) that prevents moisture from entering the holes, then filiform corrosion doesn't happen.

But washing the trailer to remove formerly airborne particles that settled on the trailer doesn't prevent filiform corrosion.

right.... but if they polish the skin... they are working on the thin coating of pure alu... that is what get mirro finished... and then because you don't have any extra alu.. which won't corrode or other... you get the rest of the alu sheet working... turning things into little worms of white things... called fil-form corrosion.. that becomes innergranular corrosion... which is the killer.. when you put two pieces of alu togeather with a fastner...

So when they polish the outside of the trailer... you are on borrowed time as your taking the protection away from the alu sheet its made from... and eventually when you polish down through the think coating of pure alu... you will find that you no longer get that polished look.. and instead you start getting a white powder on the surface... that by the way is the magnisium which is the strength of the alu sheeting...

If you get to that point.. you done... as it will disagrate quite quickly from that point on... and the only fix is to replace the sheet...

been working on Aircraft for over 50 years... in the industry.. been their seen that.. kinda thing..
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Old 11-04-2017, 02:09 PM   #7
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Quote:
Originally Posted by Dingo Girl View Post
If Airstream buys their sheets pre-coated that would explain the filiform that I've seen all along the edge of a panel on some of the newer ones.
They must have to trim an edge then there goes the coating.
Airstream was/is not doing anyone any favors by coating them.
Indeed... they are cutting cost...

Years ago they would clear coat the whole trailer when finished... this then would keep any moisture away from the fastners and sheet edges...

but they quit doing that and went to manufactured coated sheets... that still need to be worked into the trailer... i.e cheap...

I am waiting for AS to start doing like avion did.. and start using chemical conversion coatings for the skin... you will never see a later avion with corrosion or anything else... on the skin...

Its a process that doesn't cost much.. but will give the alu sheeting ... as we say... belt with suspenders... to protect it...

That is why we promote using alodine... when you re-finish the exterior skin... (actually I do it to every part that is alu...) and then if you want to clear coat or paint it... your only steps away... as we use the alumiprep, alodine, zinc cromate...and then paint... or clearcoating...

and yes your can get alodine in clear... and not coromate if your just going to clear coat...

I have seen alu then have a 7 year protection ... just from the alodine... conversion coating.. that doesn't do much to the skin in appearance...


I think you will see airstream go that way in the future... as indeed we are seeing others having corrosion problems in 2-3 year old trailers... go figure...
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Old 11-04-2017, 03:06 PM   #8
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Oh darn, or as H.G.Wells wrote in The Time Machine, “Very simple was my explanation, and plausible enough---as most wrong theories are!”

Those skin-eating Morlocks may get me after all.
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Old 11-04-2017, 03:46 PM   #9
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Oh darn, or as H.G.Wells wrote in The Time Machine, “Very simple was my explanation, and plausible enough---as most wrong theories are!”
If all else fails, you might consider a career in astronomy, which is the one branch of science where more discoveries are made by talented amateurs than by trained professionals! And it's a (fly at) night job, besides!
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Old 11-04-2017, 04:11 PM   #10
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If all else fails, you might consider a career in astronomy, which is the one branch of science where more discoveries are made by talented amateurs than by trained professionals! And it's a (fly at) night job, besides!
I was made for that because I may be laying in the gutter, but I'm still looking up at the stars.
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Old 11-04-2017, 04:19 PM   #11
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Clear coat, keep it sealed with anticorrosion and/or Walbernize.
Filiform corrosion must be removed then clear coat reapplied and sealed as above. Never use steel wool on the aluminum, it will turn black in time. Use aluminum wool or Scotch Brite.
Proper polishing does not remove metal. It rearranges the molecules and the wax seals the surface. For longevity I prefer polishing. All the Airstreams ever built can be polished, but you must remove the clear coat first. However, only the (old) clad ones can be mirror polished. The others, not quite as shinny.
You really need to wax every six months and be sure to wax the rivet heads and cut edges. Also applying an anticorrosive agent is not a bad idea. After 12 seasons my only filiform is around the Dzus fasteners were screw drivers have scratched the surface.
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Old 11-04-2017, 04:42 PM   #12
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I was made for that because I may be laying in the gutter, but I'm still looking up at the stars.
Continuing in the same vein, but off-topic, a quote from actor Dean Martin: "You're not really drunk if you can lie in the gutter without holding on!"
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Old 11-04-2017, 07:37 PM   #13
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Avoiding Corrosion and Filiform - Just Add Water?

Is this a problem for those of us who don't want to worry about it; i.e., will it eventually cause us to stop truckin’ down the road, or is this something that will just eventually mature into something like an old Volvo of indeterminate years where it would be impolite to stare?
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Old 11-04-2017, 09:24 PM   #14
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Is this a problem for those of us who don't want to worry about it; i.e., will it eventually cause us to stop truckin’ down the road, or is this something that will just eventually mature into something like an old Volvo of indeterminate years where it would be impolite to stare?
Filiform corrosion is mostly cosmetic, in that it looks bad when it starts to spread. It's unlikely to cause structural damage. Kind of like the wrinkles we all acquire as we get older. Some people fret about wrinkles, others accept them and move on.
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