This is why you MUST prime!

[nohoflyer]

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.

[docjjrmd]

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."

[PilotjohnS]

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.

[abwaldal@gmail.com]

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

[Everwild]

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.

[Blw2]

Originally Posted by PilotjohnS

......this is one of the many reasons I primed everything.

so, did you prime all surfaces of every part before assembly?

[sailsunfurled]

Originally Posted by Everwild

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.

[CaptPausert]

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

[KTOA]

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.

[Dozer]

Originally Posted by lr172

+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.