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This is why you MUST prime!

Dozer

Member
I left several sheets outside my garage for 1 month. Terrible corrosion.

Alclad doesn't protect anything.
It works just to keep the metal shine on the way from manufacture to your garage. But you will get corrosion immediately after you put your plane outside your garage.

IMG_7974 by Dozer, on Flickr
IMG_7975 by Dozer, on Flickr
IMG_7978 by Dozer, on Flickr
IMG_7977 by Dozer, on Flickr
 
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Location, location, location.

My '55 C180 had no corrosion until, in '91, it spent 6 months tied down outside of Philadelphia. That's still the only corrosion it has. The rest of its life was spent in the dry midwest except for 3 years in a tight hangar in Oxnard, CA, that didn't add any new corrosion. I've had it since '86 and know it pretty well.

Dave
 
Considering that I can SEE the beach from my hangar....yes.
Shade hangars here are the worst. The salt spray settles on the plane, and the dew keeps it working. Better to leave it outside so the sun can dry it and the rain gives it a wash.
 
The last two pictures seems to be a filiform type of corrosion under the protective layer of plastic. I had similar when I started building 16 years ago. Over a decade I keep my unpainted RV outside and didn't notice severe corrosion. There are spots like yours on access panels but nothing major.
 
Were the panels still covered with the "protective" vinyl?
I had filiform corrosition on parts of the empennage (still with the vinyl) when stored in a basement garage (read high humidity) in the middle of Europe, far from any ocean and salty air. Removed the vinyl, and never saw corrosion since.
 
Your geography will vary.

Here is a study that says 50 miles. That pretty much covers Naples, FL.

4 miles is pretty close. Whitecaps and breeze keeps the aerosols going. 2023 alloy needs the best protection, 6061 is pretty immune according to DOD studies.

Now (waiting) for the chromate discussion. :eek:
 
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The last two pictures seems to be a filiform type of corrosion under the protective layer of plastic. I had similar when I started building 16 years ago. Over a decade I keep my unpainted RV outside and didn't notice severe corrosion. There are spots like yours on access panels but nothing major.

+1

That looks exactly like the corrosion that appears regardless of salt when the plastic covering is left on. You can even see the outline of exactly where the plastic lifted off the metal due to the curvature, leaving that perfect little pocket to hold moist air and slow evaporation.

Larry
 
I had one particularly sweaty build session in my hangar a few years ago. I returned to my project a week later and there were several large areas undergoing corrosion. I couldn’t believe it.
 
Blue vinyl and corrosion

Seems to me Van's has answered this. Don't leave the vinyl on. I expect most planes get painted so I am unsure why the extra step to strip vinyl only from rivet holes on skins when all evidence points to leaving the vinyl on is risky. My understanding is Van's installs the vinyl before punching as a manufacturing protection step. Sooner it comes off the easier and better.

From KAI Section 5 -12is

"5.12 VINYL COATING
Many of the alclad parts are supplied with a thin (usually blue) vinyl coating to prevent scratching during the manufacturing of the
parts. The vinyl may be left on during drilling but should be removed for dimpling, priming and final installation. It is possible to
remove strips of vinyl along rivet lines with a soldering iron. Carefully round and smooth the tip of the iron so it will not scratch the
aluminum. The time in labor required for this added protection during construction should only be considered of value if you intend
to leave the airplane polished bare aluminum. If you intend to paint, the preparation process will include scuffing/deglossing all of
the skin surfaces anyway to provide good paint adhesion.
The adhesive on the vinyl strengthens with age, so if the coating is left on for more than a few weeks, it may become very difficult to
remove. Corrosion has been found under the vinyl in some instances. If vinyl covered parts must be stored for long periods remove
the vinyl first."
 
Like so many

Like so many before me, i started out building the perfect airplane.
I used an soldering iron and cut nice little lanes along the rivet holes.
But I soon found out that the Alcad is really soft, much softer then the underlining aluminum. The iron easily scratched the surface of the Alcad. So I stopped doing that. Since the Alcad scratches really easily, this is one of the many reasons I primed everything.
 
Well I for one will say that 4 miles from an active ocean is no way far enough Maybe if you were close to the Puget sound and it being salt water yo might be ok. But not for me.

Maybe 50 miles, But, that depends on the prevailing winds.
Salt in the air seems to stay up there for quite a long way.
Buy a Harley and park it outside and find out how bad it can get. You will soon be covering it up.
My luck is better Art
 
Cessna's Perspective

I'm building a -10 and decided to prime with epoxy primer. Location and mission are important factors IMO. I found a map that Cessna produced as part of a Service Letter. Search for "Cessna corrosion map" if you want to download it in its entirety.

I'm near Lake Erie and was surprised the Great Lakes region is also considered an area with higher than normal corrosion risk.
 

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I'm building a -10 and decided to prime with epoxy primer. Location and mission are important factors IMO. I found a map that Cessna produced as part of a Service Letter. Search for "Cessna corrosion map" if you want to download it in its entirety.

I'm near Lake Erie and was surprised the Great Lakes region is also considered an area with higher than normal corrosion risk.

I am using Alodine then 2 part primer. My aircraft factory(garage) and home is situated on a canal leading to Pensacola bay. I insulated during home construction and installed a mini split in garage to control temperature and humidity when we started this project earlier this year. Trying to mitigate issues.
 
My day job is as an engineer specializing in corrosion on the USAF T-6 Texan II trainer so I thought i would put in my two cents. This plane has Alodine, chromate primer inside and out and a two-part topcoat. as well as wet installed fasteners and sealed faying surfaces and we still have corrosion issues in some locations.

Corpus Christi is the worst we get all kinds of corrosion there but even other location in non-severe locations have corrosion wherever the coatings are damaged it just takes longer to appear. we have some aircraft there less than 15 years old that are having to get major repairs (new wings on some).

Granted our aircraft are used pretty rough and stored outside under covered shelters instead of hangers but my experience so far has been that you need some kind of corrosion protection. I would make sure to pay special attention to coating any areas that will be difficult to inspect on a regular basis and you should make sure that you do a thorough corrosion inspection as part of your annual maintenance. especially in areas where steel and aluminum parts touch. We have also started using Cor-Ban 35 quite a bit and Cor-ban 27L on latches and stuff (27L doesn't dry)

I am considering building an RV-9A currently and I will be priming all of my parts. Even though I live in Oklahoma and that is a low severity area I am planning enough trips to Florida the Bahamas etc. that I do not want to end up with major corrosion issues 10 or 15 years down the road. Of course, I am only 35 so my plane is going to have to last me a while:D
 
Ocean Fog = Salt Storm

SoCal Edison calls the fog that comes in from the ocean a salt storm. Salt is conductive and electricity can track across it.

They have an ongoing preventative maintenance plan which includes spraying/cleaning electrical insulators on a regular basis.

At my last job they sprayed the company's two electrical substations insulators twice a year with DI water. Would I sit in a spray truck and high pressure spray 66kV (and higher) insulators for a living ... nope.
 
+1

That looks exactly like the corrosion that appears regardless of salt when the plastic covering is left on. You can even see the outline of exactly where the plastic lifted off the metal due to the curvature, leaving that perfect little pocket to hold moist air and slow evaporation.

Larry

EXACTELY!!!!! And now think about metal to metal contacts, like ribs to the skin and other overlapping areas. All the same - "perfect little pocket to hold moist air and slow evaporation."

That is why we all need prime all parts. I use PreKote+Scotchbrite and Akzo Epoxy primer. Incredible adhesion to aluminum. But you better wait 48 hours before riveting parts. 24 hours are not enough.
 
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My day job is as an engineer specializing in corrosion on the USAF T-6 Texan II trainer so I thought i would put in my two cents.... We have also started using Cor-Ban 35 quite a bit and Cor-ban 27L on latches and stuff (27L doesn't dry)

Brian, please tell us more about the two Cor-Ban products. Can you share how they were selected, comparisons with other similar products, etc? In your trade, are "creep in between" inhibitors a big deal, or mere insurance, or something else?

https://zipchem.com/categorie-produit/cor-ban/
 
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Human nature to follow the crowd . . . . or not.

Like so many before me, i started out building the perfect airplane.
I used an soldering iron and cut nice little lanes along the rivet holes.
But I soon found out that the Alcad is really soft, much softer then the underlining aluminum. The iron easily scratched the surface of the Alcad. So I stopped doing that. Since the Alcad scratches really easily, this is one of the many reasons I primed everything.

This same experience (small scale as I tested the process) applies to many popularized processes that have been posted without warnings, or even knowing the risks. It taught me to be much more careful in my build, and not blindly copy others (applied widely). Skill and technique makes a huge difference in the outcomes of many building practices. Advance learning/testing is fundamental, or these days . . . just follow the (well written) instructions.
 
Sorry about taking so long to reply on this. The Cor-ban research was done by the C-5 program so I had to get some details.

The C-5 program did some testing a few years ago and had best results with Cor-Ban 35. I asked for the results but haven't gotten them yet.

Part of the reason for use of Cor-ban 35 vs something like corrosion X is that Cor-ban 35 is a dry film protectant. Corrosion X does not dry. Once Cor-ban 35 is applied it stays on the part unless damaged. It is also water displacing.

Please note we have discovered that Cor-ban should never be applied over electrical equipment as electric sparks can cause flammability issues.
 
Sorry about taking so long to reply on this. The Cor-ban research was done by the C-5 program so I had to get some details.

The C-5 program did some testing a few years ago and had best results with Cor-Ban 35. I asked for the results but haven't gotten them yet.

Part of the reason for use of Cor-ban 35 vs something like corrosion X is that Cor-ban 35 is a dry film protectant. Corrosion X does not dry. Once Cor-ban 35 is applied it stays on the part unless damaged. It is also water displacing.

Please note we have discovered that Cor-ban should never be applied over electrical equipment as electric sparks can cause flammability issues.

Thanks for this information Brian! Look forward to hearing from you once you have the test results.
 
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