Surface sheet corrosion treatment

[Mooney-Shiner]

Hello, the highly esteemed forum!

I moved my aircraft from Tennessee down to Florida, and the year later comes out the surface corrosion on the top sheets! The price of being in Florida..

How do I treat and prime the fact that the areas? I did the search for corrosion but all I could find was the corrosion X treatment for the insides. Already completed that procedure.

 

I heard something about etching on the bare metal and zinccromate.

 

Can somebody point a newbie in the right way?

 

Much respect to everyone!

 

 

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[ArtVandelay]

Is your paint peeling and bare metal is showing? I assume by top sheets you mean outside sheet metal?

[PT20J]

Check out AC 43-4B

https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_43-4B.pdf

and, AC 43.13-1B

https://www.faa.gov/documentlibrary/media/advisory_circular/ac_43.13-1b_w-chg1.pdf

 

[Mooney-Shiner]

Is your paint peeling and bare metal is showing? I assume by top sheets you mean outside sheet metal?

The paint mostly blistering.

Sorry for misnom. I meant to say “outside skins”


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[ArtVandelay]

The paint mostly blistering.

Sorry for misnom. I meant to say “outside skins”

Sounds like you need a paint job, I think anything else will just be a temporary solution.

[Mooney-Shiner]

Sounds like you need a paint job, I think anything else will just be a temporary solution.

It is VERY localized areas. Cumulatively , it is Less than 0.05% of aircraft , if that


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[A64Pilot]

12 hours ago, ukrsindicat@yahoo.com said:

It is VERY localized areas. Cumulatively , it is Less than 0.05% of aircraft , if that


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Art’s probably right, what your looking at is likely just the beginning, it will most likely advance. But anything’s possible, maybe your looking at bad spot paint areas, but most often it’s an old failing paint job.

Walk the ramp and find a old ramp tramp and see if it’s paint job is failing in a similar but more advanced manner

Edited October 2, 2021 by A64Pilot

[Mooney-Shiner]

15 hours ago, Freemasm said:

You’re going to get a million opinions here. Weigh them all and proceed. My two cents =
 

buy a spot rivet blaster and bead blast the area. This will get the corrosion out of the pits other mechanical means won’t.

acid etch will help but not critical IMO for a repair if you properly blasted the surface.  
 

alodine the surface will promote adhesion and protect surface from future attack.  It contains heavy metals that never leave the environment or your body.  PreKote is a decent adhesion promoter and very safe. Does basically nothing for corrosion prevention.  
 

zinc chromate is a great corrosion protector but has heavy metals like alodine.  Hexavalent Chrome is nasty stuff.  See above  

I’d start waxing that machine if you’re going to keep it down here. Corrosion can total your investment  

Other opinions to follow. 

I like the spot blaster idea! What media did you use? Walnut, Sand or grass bead?

[Guest]

8 hours ago, ukrsindicat@yahoo.com said:

I like the spot blaster idea! What media did you use? Walnut, Sand or grass bead?

I’m not sure that blasting the skin is a good idea.  If the spots are as small as you describe, some 3M Scotch brite pads, alumiprep 33, some Alodine, some epoxy primer and touch up paint would work just as well.

Clarence

[A64Pilot]

Our skins are I’m sure 2024 aluminum, which is Alclad.

https://www.corrosionpedia.com/definition/65/alclad

Alclad is a layer of pure aluminum layered onto a less corrosion resistant but stronger aluminum alloy, pure aluminum is very corrosion resistant, however the pure aluminum is soft and very thin layer and pretty easily removed, which of course greatly reduces the corrosion resistance.

So be very careful with blasting or whatever means you use to prep the metal as you don’t want to remove the Alclad, because it’s very corrosion resistant.

I have heard but cannot verify, but  Alclad is the primary reason why there are so many more US WWII aircraft than other countries aircraft, theJapanese for instance used a strong and light alloy in their Zero’s but as it wasn’t Alclad, they corroded much faster.

Alclad is an Alcoa product and goes back to before WWII

[Guest]

7 hours ago, Freemasm said:

A rivet Spot blaster is a siphon device lhat should be limited 60 psi. It is very easy to use by anyone including a first timer. Glass bead will be fine in this app. Aluminum oxide is very soft and will remove easily. The bead will clean pits were other mechanical means can’t without removing parent material. Likewise, if someone out 100 psi through the device, uses garnet, and/or dwells on the the affected area longer than needed to remove the corrosion then they probably deserve the outcome. 

Give me an f’ing break. 2024 is the alloy. That designation has nothing to do with the cladding process. If it's not marked as such don't assume it's clad. Clad versus unclad materials have different properties. You technically can't sub alcad if drawing don't specify or allow substitution though this is rare. If the paint is blistered, the corrosive attack extends beyond the clad layer which applied in tens of thousandths of an inch. Commercially pure Al isn't as corrosive resistant has some would believe. When it does oxidize, the reactivity of the resulting layer is relatively low.  

Don’t get your panties in a bunch.  His opinion is just as valid as yours or mine.

Clarence

[A64Pilot]

I can assure you that all GA aircraft are manufactured with Alclad sheet, and Alclad from memory is 5% of the thickness of the sheet, and just going from feel it seems our fuselage skins are about .020 or so, which is awful thin, but as they aren’t structural, they don’t need to be thicker, thin skins have even thinner Alclad 

Bare sheets can be sourced, but I’ve never seen it used on exterior aircraft skins.

The OP should I think buy an aircraft painter lunch and ask their opinion on method of repair.

On edit, the issue with using any kind of mechanical means to remove paint from an aircraft to include blasting is that modern polyurethane paints are so much tougher than the pure aluminum they are painted onto.

Edited October 3, 2021 by A64Pilot

[1980Mooney]

13 hours ago, Freemasm said:

Give me an f’ing break. 2024 is the alloy. That designation has nothing to do with the cladding process. If it's not marked as such don't assume it's clad. Clad versus unclad materials have different properties. You technically can't sub alcad if drawing don't specify or allow substitution though this is rare. If the paint is blistered, the corrosive attack extends beyond the clad layer which applied in tens of thousandths of an inch. Commercially pure Al isn't as corrosive resistant has some would believe. When it does oxidize, the reactivity of the resulting layer is relatively low.  

Maybe I am missing your point but the original poster needs to assume that he is dealing with alclad skins. And if as you say “the corrosive attack extends beyond the clad layer”, physical means of cleaning, regardless how “gentle” the abrasion, may tend to remove more of the compromised clad. That is why small spots need to be treated and stopped before they get too large. Otherwise you are just chasing your tail. Sitting in Florida or along the coast you may see the corrosion reappear fairly rapidly once the clad is materially damaged/breached/removed.  
https://www.avweb.com/ownership/the-savvy-aviator-19-thwarting-corrosion/
https://www.experimentalaircraft.info/articles/aircraft-aluminum.php

 

Edited October 3, 2021 by 1980Mooney

[Guest]

2 hours ago, Freemasm said:

Interesting. Giving someone an option to clean corrosion is an opinion. Technical topics like engineering, metallurgy (and related processes), chemistry (oxidation, reduction, passivation, etc.) don't give a crap about anyone's opinions. I'll stop there.

The OP said outer skins. A little vague but he's trying to learn. He didn't say fuselage that I saw. If this is a wing, aero-surface skin, etc. it is semi to full monocoque design/construction and is indeed structural.

Postings based upon anecdotal "evidence" are in no short supply here or elsewhere. Some here on MS are quite (in)famous regarding such. I've been an engineer, dealt-with, hired and lead them for decades now. The ones that fall into the unconscious/confident category/quadrant (don't know what they don't know) can be the most dangerous and require the most supervision. They're quickly sniffed out and their future responsibilities reflect such until they can find something else. 

Opinions are like cowboy hats...... 

 

If you have to resort to cursing to get your across, you need to brush up on your communication skills.

 

Clarence

[ilovecornfields]

I think you’re the only one who’s laughing. To everyone else, you’re coming across as someone who had a narcissistic injury and lacks the executive function to not keep replying. Hopefully that is more developmentally appropriate language for you.

[PT20J]

Kind of interesting that we can have so much discussion about a basic repair that every working A&P and paint shop does on a regular basis.  

[DCarlton]

10 minutes ago, PT20J said:

Kind of interesting that we can have so much discussion about a basic repair that every working A&P and paint shop does on a regular basis.  

Starting to wonder if there's an SOP somewhere or if everyone does it the same.  Friend of mine is wondering how to repair a small BONDO like patch on his Piper wing that bubbled.  That'all probably generate a debate too.   Clean, treat, prime, fill, sand, etc... but with what.  

[Guest]

No one here know everything, I enjoy sharing my knowledge and equally am amazed at the things I learn about Mooney’s and airplanes in general.  I try to post factual info as much as possible backed with my own personal experience.

From the J maintenance manual, here are the skin call outs, they’re clad skins, which is where my involvement started.

Clarence
 

 

[Mooney-Shiner]

On 10/2/2021 at 8:03 PM, M20Doc said:

I’m not sure that blasting the skin is a good idea.  If the spots are as small as you describe, some 3M Scotch brite pads, alumiprep 33, some Alodine, some epoxy primer and touch up paint would work just as well.

Clarence

Doc, thank you for the advise. Do you use scotch brite pads for the dremmel? I don't think I will be able to pop the blistered paint with square pad alone.  Any recommendations for the epoxy primer?

How do you get touch up paint? Should I have PPG blend the car paint for me?

Thank you!