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Thread: Priming inside super cub wings

  1. #1

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    Priming inside super cub wings

    What is the best way or product to corrosion proof your assembled super cub wings internally before you cover.

  2. #2

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    I like Variprime on leading edges. Internals didn't get coated.
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  3. #3
    Steve Pierce's Avatar
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    I use PPG epoxy primer.
    Steve Pierce

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    Stewart Systems epoxy primer. Click image for larger version. 

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    PA-12 N418BS
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    Gotta ask. Why? Priming is a prep coat for a top coat. I recall a discussion here about priming airframes and the consensus was primer required a top coat to protect the airframe. Why prime surfaces not intended to be finished?
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  6. #6
    Steve Pierce's Avatar
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    Quote Originally Posted by stewartb View Post
    Gotta ask. Why? Priming is a prep coat for a top coat. I recall a discussion here about priming airframes and the consensus was primer required a top coat to protect the airframe. Why prime surfaces not intended to be finished?
    You are correct on steel but with aluminum in a humid environment primer can keep the aluminum from corroding.
    Steve Pierce

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    It seals aluminum but not steel? How?

    My 45 year old Cessna seaplane had internal zinc chromate coating. Zinc chromate is sacrificial. It wears out. Where the primer is gone? Not a speck if corrosion where I can see it. SID instructions advise looking into places I can't see. Places primer can't reach. I'd think Ribs and spars in a Cub would have the same thing if we disassembled one that parked outside for 45 years without inspecting it in the nooks and crannies. That doesn't happen. Sometimes more is better. Sometimes more is just more. Interesting topic.
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    Steve Pierce's Avatar
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    I don't why but just like your experience with your Cessna with zinc chromate, everything I have rad and my own experience has been good with epoxy primer only on aluminum. I have primed assembled wings and I have also primed every part prior to assembly. I have seen unprimed Pa=iper wings look like new and I have seen them look like an old cessna based in Florida all it's life. It probably has to do with humidity and the fact that aluminum is less prone to corrode unfinished than steel is.
    Steve Pierce

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    www.SkupTech.com mike mcs repair's Avatar
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    Quote Originally Posted by stewartb View Post
    I like Variprime on leading edges. Internals didn't get coated.
    That’s stitts epoxy. Variprime will melt with the glue


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  10. #10
    www.SkupTech.com mike mcs repair's Avatar
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    Unprimed corosion. https://photos.app.goo.gl/otXYGZ5bTBZptLMx5


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  11. #11

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    Quote Originally Posted by stewartb View Post
    Gotta ask. Why? Priming is a prep coat for a top coat. I recall a discussion here about priming airframes and the consensus was primer required a top coat to protect the airframe. Why prime surfaces not intended to be finished?
    From my Steel Structures Painting Council days, this would be due to the anchor pattern created in the surface during the blasting process on the frame. The primer may/will not cover it sufficiently and when it cures, the peaks of the anchor pattern can poke thru and rust. Not to say someone hasn't ever but I've never seen sand blasted aluminum so no peaks = no "salt and pepper" corrosion. Now proper adhesion without an anchor pattern to grab ahold of takes a good epoxy primer and good cleaning prep.
    Remember, These are the Good old Days!

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    To tell you the truth I did not know Variprime was still on the market. I have been through many gallons of that.
    Anyone using Alodine on the inner surfaces. I have used allot of it both inside and out, it was the basic etch before the Variprime. Only coating on the inner surfaces.
    I used to stick test samples in the dirt, pull them up every few years and drive them back in. Many years went by before a Variprime steel tube started showing coating failure, that sample like most that I did was partly top coated with Imron. The Imron area was not even scuffed from being driven in the soil. There were left in the soil when I moved away from the 25ish years ago. Wonder how the have held up.
    Regards, Charlie
    Super Coupe E-AB build in process
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  13. #13

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    Quote Originally Posted by KJC View Post
    Stewart Systems epoxy primer. Click image for larger version. 

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    When priming an assembled wing, thorough surface prep must be a nightmare.
    Is priming unprepared (un-scuffed) areas worse off than Just leaving the metal bare?
    Is there an etching aluminum primer?

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    In 1966 my mechanic said "just fog everything with zinc chromate (no longer available here). I did. Still no visible corrosion. Four miles from ocean, but Mediterranean climate.
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    Quote Originally Posted by bob turner View Post
    In 1966 my mechanic said "just fog everything with zinc chromate (no longer available here). I did. Still no visible corrosion. Four miles from ocean, but Mediterranean climate.
    bob, i did the same thing,still available, only surface prep was a pressure wash and air hose, lightly misted before the leading edges went on with this and called it good.https://www.bac-online.com/default.a...de=ZC701#tab-1
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  16. #16

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    Zinc Chromate is interesting stuff since the zinc only works when wet and it's sacrificial so by design it doesn't last forever. And in order to work the base carrier has to be porous so once the zinc is consumed the coating does nothing. My Cessna doesn't have much corrosion that I can see so I wonder how effective the 45 year-old zinc chromate seaplane treatment is today.

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    I've been debating this with a set of built-up Javron wings. I'm using the Stewart covering system and have debated whether or not to shoot a protective coat on all exposed surfaces, which would be a nightmare. Intend to keep the plane on wheels, so float plane consideration not an issue. Guess everyone is going their own way on this.

  18. #18

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    Quote Originally Posted by wdoubleday View Post
    I've been debating this with a set of built-up Javron wings. I'm using the Stewart covering system and have debated whether or not to shoot a protective coat on all exposed surfaces, which would be a nightmare. Intend to keep the plane on wheels, so float plane consideration not an issue. Guess everyone is going their own way on this.
    from all I’ve gathered on this subject,
    Away from corrosive environment, leave it bare. Bare Aluminum has pretty good anti corrosive properties.
    Scuffing, ruffing surface increases surface area prone to corrosion if and when coating breaks down/fails.
    Otherwise, do a damn good and thorough prep and coating job or you’re wasting time on a false sense of security against corrosion.
    my 2c
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  19. #19
    Steve Pierce's Avatar
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    If you are in a decent environment I doubt you will see corrosion in your lifetime.
    Steve Pierce

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    Will Rogers
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  20. #20
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    Quote Originally Posted by wdoubleday View Post
    I've been debating this with a set of built-up Javron wings. I'm using the Stewart covering system and have debated whether or not to shoot a protective coat on all exposed surfaces, which would be a nightmare. Intend to keep the plane on wheels, so float plane consideration not an issue. Guess everyone is going their own way on this.
    Fresh water use is also not a float plane issue. More importantly is the atmospheric environment where the plane will live. If it will live in a coastal, highly humid and/or acidic environment protect it. If it lives in a dry desert, forget it. In between use your own judgement. Give us a clue as to your location. Then we can give you a more accurate answer.
    N1PA
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    I have coated a few for customers over the years at their request, but for the most part I leave bare in this part of the country. I have seen very little corrosion in wings dating back to the early forties. All about your mission and where you live I think. I bought a 39' J-3 in Jacksonville in the mid 70's and flew it here to Maine. It was in old cotton and needed covering. It had spent it's life in Florida and the wings were clean, and the fuselage was very good too. It obviously varies from one case to the next.
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  22. #22

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    priming wings is like insulating a house, lots of ideas.

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    I think the biggest threat to wings in the Midwest comes from mud daubbers and mice.
    In spite of factory coated (?) wings (1979 cub, Steve?)
    This Cub was parked in a barn and flown infrequently.
    Mouse nests soaked in pee along false spar resulted in corrosion around all hangars requiring replacement of false spar on both wings.
    I probably got 10 lbs of mud out of both wings as well.

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