I'm just starting my RV-7 tail and I'm not really sure what is considered "good, Prudent" corrosion protection for the inside. I'm comfortable with how to prep and complete the exterior surfaces, but I'm kind of thinking of maybe just spraying a coat of zinc chromate on the inside surfaces. I know you should remove all the ALCLAD on the exterior as part of the prep, but is this necessary/prudent on the interior metal?
Van's Air Force
Don't miss anything! Register now for full access to the definitive RV support community.
corrosion protection
- Thread starter jacksel
- Start date
Kyle Boatright
Well Known Member
You absolutely DON'T want to remove the alclad from any part of your airplane - inside or out. The alclad is a huge corrosion barrier. Yu might want to scuff it to provide "tooth" before exterior primer/paint. But that's a roughing up process, not removal.
Zinc Chromate (or epoxy, or...) is a fine corrosion preventative for the inside of structures. Do make sure you use something to protect the non-alclad parts in your airplane like any extruded angle.
Zinc Chromate (or epoxy, or...) is a fine corrosion preventative for the inside of structures. Do make sure you use something to protect the non-alclad parts in your airplane like any extruded angle.
Corrosion Protection
Alclad is a coating of pure aluminum applied over the alloy sheet, as Kyle said, for corrosion protection. The sheet material used in RV aircraft is 2024-T3 a copper based high strength aluminum alloy. It is available in bare (no cladding) or Alclad which is what is supplied with the kit. DO NOT REMOVE ALCLAD.
Van's assembly instructions tell you to primer all non-alclad parts, again as Kyle said, these will be other alloys such as 6061-T6 extrusions. The instructions also say primer is optional for alclad parts. This has been discussed at some length, see "Primer Wars".
Most certificated aircraft are not primered and for the most part are still in service after 50 years with little corrosion. However, this depends where the aircraft spends it's life, coastal/high humidity areas are the worst, desert/dry areas are the best.
In my view, Alumiprep 33 etch, Alodine 1201 followed by a two part epoxy primer is the best solution as I live in a coastal/high humidity area. However a single stage etching primer should still give good protection. Another way to provide internal corrosion protection is to apply Dinitrol or similar spray to a completed airframe. However this will bleed out the lap joints, so the external surfaces should be painted first. It also stays somewhat sticky, so is less pleasant for maintenance or installing equipment after application.
Alclad is a coating of pure aluminum applied over the alloy sheet, as Kyle said, for corrosion protection. The sheet material used in RV aircraft is 2024-T3 a copper based high strength aluminum alloy. It is available in bare (no cladding) or Alclad which is what is supplied with the kit. DO NOT REMOVE ALCLAD.
Van's assembly instructions tell you to primer all non-alclad parts, again as Kyle said, these will be other alloys such as 6061-T6 extrusions. The instructions also say primer is optional for alclad parts. This has been discussed at some length, see "Primer Wars".
Most certificated aircraft are not primered and for the most part are still in service after 50 years with little corrosion. However, this depends where the aircraft spends it's life, coastal/high humidity areas are the worst, desert/dry areas are the best.
In my view, Alumiprep 33 etch, Alodine 1201 followed by a two part epoxy primer is the best solution as I live in a coastal/high humidity area. However a single stage etching primer should still give good protection. Another way to provide internal corrosion protection is to apply Dinitrol or similar spray to a completed airframe. However this will bleed out the lap joints, so the external surfaces should be painted first. It also stays somewhat sticky, so is less pleasant for maintenance or installing equipment after application.
Pat Stewart
Well Known Member
Kyle and Terre are spot on. Also if you put any primer on the exterior a good painter will take it off prior to prepping your aircraft for paint.
Pat
Pat
Jack Tyler
Well Known Member
One point underemphasized in 'Primer Wars' threads...
...and I've read a number of them (including a batch that have been archived) is Terrye's point about post-construction anti-corrosion treatment. It's true that most (all?) GA a/c did not receive interior anti-corrosion treatment of any kind when being manufactured. And many locations in the USA that are densely populated with GA a/c are near the Pacific, the Atlantic, and the Gulf of Mexico. Has corrosion control been ignored by owners of all these a/c? Nope, some owners choose to periodically spray the a/c's interior with a product like ACF-50, which lasts for some years (length of time somewhat debatable and dependent on the application).
There are benefits to this approach, including the fact the a/c weight isn't increased during construction and the speed of assembly isn't affected, both due to priming. Yes, sprays like ACF-50 dribble out of the joints for a while but that doesn't last and I found maintaining a relatively fresh paint job no less difficult after the initial 'drip' period. And I found ACF-50 very effective over a span of 5 years. (FYI this was when owning an AA-5 that was based right on Tampa Bay at St. Pete, Florida's downtown airport, SPG).
I mention all this because I found very little time given to this option in a few of the primer threads' discussions, and it not being mentioned at all in the rest of them. It really is a viable option.
Jack
...and I've read a number of them (including a batch that have been archived) is Terrye's point about post-construction anti-corrosion treatment. It's true that most (all?) GA a/c did not receive interior anti-corrosion treatment of any kind when being manufactured. And many locations in the USA that are densely populated with GA a/c are near the Pacific, the Atlantic, and the Gulf of Mexico. Has corrosion control been ignored by owners of all these a/c? Nope, some owners choose to periodically spray the a/c's interior with a product like ACF-50, which lasts for some years (length of time somewhat debatable and dependent on the application).
There are benefits to this approach, including the fact the a/c weight isn't increased during construction and the speed of assembly isn't affected, both due to priming. Yes, sprays like ACF-50 dribble out of the joints for a while but that doesn't last and I found maintaining a relatively fresh paint job no less difficult after the initial 'drip' period. And I found ACF-50 very effective over a span of 5 years. (FYI this was when owning an AA-5 that was based right on Tampa Bay at St. Pete, Florida's downtown airport, SPG).
I mention all this because I found very little time given to this option in a few of the primer threads' discussions, and it not being mentioned at all in the rest of them. It really is a viable option.
Jack
rv9aviator
Well Known Member
What Jack said!!!!! I won't prime my next kit if there is one.
Sent you a PM!
Sent you a PM!
Last edited:
GusBiz
Well Known Member
Evidence vs Theory
I don't like to speak like an expert because who the h3ll is an expert, I did a degree in industrial chemisty in University and then worked for Ferro Corp for a number of years as an analytic chemist. So I know a bit more science about this than most but it doesn't mean I know that much. But I will say this I have a fair amount of expereince in knowing when I can rely upon chemical facts and when its a bit of pot luck.
I think this is a case of reality on an individual basis versus advice for a population.
This is why there is a "primer wars" article.
One guy can testify black and blue with real evidence that there is no need for primer anywhere because he sits his aircraft on the beach and when the water comes in for high tide it half gets covered by salt water and 40 years later there isn't a single sign of corrossion and you can come over and see proof so there is no need for primer and etc etc.....
Now would you make that an FAA ruling? h3ll no. Chemistry depends on very small paramiters that sometimes are just that there was a scratch that penetrated the outer pure aluminium layer and just the right salt combination got in. Sometimes the manufactureing process provided a little more and I mean micometers of pure aluminium to that run so that particular plane really doesn't need much priming. Scientifically if you took measurements there is a higher layer of protection.
So you end up getting a bunch of us who don't take measurements/samples/evidence and we just look at what we have done and then we start talking about how it all works like what we have done/seen is real and is a good example of how real ife works.
The truth of all of this is, priming adds a categorically real, physical layer of protection from corrosion. Sometimes in the right circumstances you just don't need it. Can you guarantee those circumstances? No, so do you need priming? Do you need a helmet while flying? Do you need a 5 point harness vs a 4 point? What does a 5 point give you that a 4 point just doesn't?
In the end it is a matter of risk management and the experience of personal integrity. Did you do a good job in your mind. Do you feel like your aircraft is well built, and do you know forsure that aluminium you have is one of those that was manufactured just on the slightly lean side and really does need the extra protection.
My personal thought is not why prime it, it is why not? Its extra work yes but then again, so is building an aircraft compared to buying it second hand. Second hand is often cheaper so obviously your not building it because its less work.
There are some people who will not prime again not for any other reason other than "it was a pain in the behind and I didn't like it", and it has nothing to do with anything other than their grumpy attitude.
In the end it is cost vs benefit, like everything else in life.
I don't like to speak like an expert because who the h3ll is an expert, I did a degree in industrial chemisty in University and then worked for Ferro Corp for a number of years as an analytic chemist. So I know a bit more science about this than most but it doesn't mean I know that much. But I will say this I have a fair amount of expereince in knowing when I can rely upon chemical facts and when its a bit of pot luck.
I think this is a case of reality on an individual basis versus advice for a population.
This is why there is a "primer wars" article.
One guy can testify black and blue with real evidence that there is no need for primer anywhere because he sits his aircraft on the beach and when the water comes in for high tide it half gets covered by salt water and 40 years later there isn't a single sign of corrossion and you can come over and see proof so there is no need for primer and etc etc.....
Now would you make that an FAA ruling? h3ll no. Chemistry depends on very small paramiters that sometimes are just that there was a scratch that penetrated the outer pure aluminium layer and just the right salt combination got in. Sometimes the manufactureing process provided a little more and I mean micometers of pure aluminium to that run so that particular plane really doesn't need much priming. Scientifically if you took measurements there is a higher layer of protection.
So you end up getting a bunch of us who don't take measurements/samples/evidence and we just look at what we have done and then we start talking about how it all works like what we have done/seen is real and is a good example of how real ife works.
The truth of all of this is, priming adds a categorically real, physical layer of protection from corrosion. Sometimes in the right circumstances you just don't need it. Can you guarantee those circumstances? No, so do you need priming? Do you need a helmet while flying? Do you need a 5 point harness vs a 4 point? What does a 5 point give you that a 4 point just doesn't?
In the end it is a matter of risk management and the experience of personal integrity. Did you do a good job in your mind. Do you feel like your aircraft is well built, and do you know forsure that aluminium you have is one of those that was manufactured just on the slightly lean side and really does need the extra protection.
My personal thought is not why prime it, it is why not? Its extra work yes but then again, so is building an aircraft compared to buying it second hand. Second hand is often cheaper so obviously your not building it because its less work.
There are some people who will not prime again not for any other reason other than "it was a pain in the behind and I didn't like it", and it has nothing to do with anything other than their grumpy attitude.
In the end it is cost vs benefit, like everything else in life.
Primer
To which I would add: if you are going to prime, then investigate the proper aircraft products, pick a reputable manufacturer and do the process they recommend to the letter. Paint is an excellent barrier to corrosion whether over an aluminum or steel substrate, but only if it adheres well. If water, oil, gas, hydraulic fluid, etc. gets between the coating and the substrate, all bets are off and it is probably worse than not painting at all. So although I am 3/4 of the way through my build, and even though it is time consuming and a pain in the backside, I'm sticking with the same product and process I started out with.
To which I would add: if you are going to prime, then investigate the proper aircraft products, pick a reputable manufacturer and do the process they recommend to the letter. Paint is an excellent barrier to corrosion whether over an aluminum or steel substrate, but only if it adheres well. If water, oil, gas, hydraulic fluid, etc. gets between the coating and the substrate, all bets are off and it is probably worse than not painting at all. So although I am 3/4 of the way through my build, and even though it is time consuming and a pain in the backside, I'm sticking with the same product and process I started out with.
