Treat minor filiform corrosion

Tom-D said:
Do you understand what revisions and up dates do?
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Yes, I do. Do you?

A manual for a 1963-1968 aircraft is meant for a 1963-1968 aircraft when it is revised. A revised manual does not make it magically applicable to other models. I think there is a page that shows that.

upload_2017-4-16_10-33-21.png
 
Tom-D said:
qh jiklp'

I will ask you a question to provoke a thought.

What is the 43,13-1b? What does it apply to, and is it approved data. when you research these questions you know the answer to your own question. Start by reading the whole AC. "AC" what does that stand for?
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Here you go.

upload_2017-4-17_11-31-25.png

And I also found the following via a brief google search. The last bit is the most important.

https://www.faa.gov/about/office_org/headquarters_offices/agc/pol_adjudication/agc200/interpretations/data/interps
/2010/inter%20ac%2043-13-1b%20-%20(2010)%20legal%20interpretation.pdf
 
My trusted shop in Oregon looked at it and said they recommend removing the affected paint and corrosion, priming the area, then spray some CorrosionX from the inside at the seam. Since the CorrosionX will seep for a long time, don't repaint the area until the next annual.
 
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Excellent! Not what I would do, but a good path none the less.


PS Where is Tom?
 
After 7 pages of this thread, what I would do doesn't matter. You have a mechanic you trust, he gave you his opinion, you accepted it, a plan has been made, time to move on.
In retrospect, I should have kept my comment to "Excellent". Please carry on! :)
 
:D I was just surprised by not painting it right away, but that is the path we're taking. I trust him completely.
 
The reason for not painting immediately is due to the fact that ACF50, or Corrosion X, will seep into the cracks and crevases, then seep out on the other side, and paint won't stick. Probably should have painted before the corrosion x treatment.
 
Nothing has been done yet, I guess the Mechanic would rather have Corrosion X seep into the crack than paint.
 
Paint may/may not seal the seams from the outside. but the corrosion-x seeps in from the inside, where the paint don't get.
 
Tom-D said:
The picture you show is typical of filiform corrosion, that is what we see on small aircraft in our GA fleet.
What you show is very typical of what happens when the strippers and other chemicals get driven into the seams of the fuselage during a re-paint. now they creep out under the new layer of paint, and cause what you are seeing, this is the environment that the microbes love, it is their excrements that cause the acid that etches the aluminum.
First. Do not scrape the paint away, (Like has been suggested), use a small dab of epoxy stripper and remove about a dime sized area of paint. wash clean, wipe dry, that will allow you to see how deep the corrosion is.
Using a stainless steel platers brush remove the black corrosion products by a circular scrubbing motion and clean with a product called alum-prep sold at AS&S. continue that cycle until all black deposits are removed.
then wet with Aldine 1201 (from spruce also). then rinse and dry.
Once clean, and alodined, touch up with any paint you like.

Remember -- there is a very thin coating of pure aluminum over the base metal, you go scraping with any thing that is hard enough to remove paint and you will remove the aluminum layer and make your corrosion problem worse.

when you see his starting on your aircraft, it will soon get worse, keep a close eye on it. don't allow this to get ahead of of you.

When I see this on an annual inspection I get worried about how much corrosion is in the seam from which this spread.

Your clean metal should look like this, the lower left corner of the picture, next to the access panel.
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Thank You Tom-D for this post.

I hesitated treating the filiform corrosion on my experimental until reading this. I held my nose and followed the ensuing discussion before deciding I had waited long enough.

I acquired the necessary chemicals and went to work. The stainless thin wire brush was key to cleaning the worst bits. It quickly became obvious why this is the proper approach rather than any abrasive. Primed and paint and ready to go.

The cause of this corrosion on my project was not properly priming a non-alclad part.

Thank You!


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You are ultimately responsible for the airworthiness of your airplane.

One definition of abrasive is: a substance or material capable of polishing or cleaning a hard surface by rubbing or grinding.

The stainless brush did abrade (was abrasive to) the aluminum, however, if the area was not blended, stress risors remain which could result as crack initiation points.

Everyone should keep in mind: the methods expressed/used by an individual A&P, may not be approved, acceptable or legal for an OP to use.
 
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bluerooster said:
The reason for not painting immediately is due to the fact that ACF50, or Corrosion X, will seep into the cracks and crevases, then seep out on the other side, and paint won't stick. Probably should have painted before the corrosion x treatment.
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The suggestion I received from 2 A&Ps was the same; apply corrosionx and wait. Then in a year or so, come back and remove, prep, paint corroded areas. The wait was because paint won't stick and the X goop will seep.

Didn't quite sound right to me so I decided to remove and repair the exposed corrosion. Now I'm thinking I will simply apply a limited and targeted dose of Corrosion X to the problem area from inside.


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