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Another Question on Priming

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dfmoeller

Joined: 19 Jun 2006
Posts: 60
Location: Austin, TX

Posted: Thu Jun 07, 2007 2:22 pm Post subject: Another Question on Priming

OK.  Here is yet one more question about the black art of priming/corrosion protecting your structure.



I see that Zenith automatically applies CORTEC to interfacial areas on the parts that make up the spars they build.  They do not, however, apply the protection to the external surfaces of the spars.  By this, I'm referring to the areas where the rivet's heads and tails bear on the aluminum sandwich.



I can certainly see the wisdom of only applying primer to the interfaces between parts rather than the entire parts.  This is where the moisture will wick and cause corrosion.



My question is though, shouldn't the surfaces that will bear the rivets get the same treatment.  OR, I had a thought that perhaps the rivet's bearing surfaces form essentially a gas tight seal with the part underneath, needing no protection.



I realize that my descriptions above may be a little cryptic - sorry.  Another way to describe this would be when riveting part A to part B, I would think one should prime both sides of parts A and B rather than just the interface between A and B because corrosion could start in the interface between the rivet head and A or the interface between B and the rivet tail.  The spars aren't built like that though.



If anyone knows why the surfaces that the rivets bear on are not protected, please enlighten me!



Doug

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John Bolding

Joined: 23 May 2006
Posts: 281

Posted: Thu Jun 07, 2007 2:51 pm Post subject: Another Question on Priming

Not a chance, easy to demonstrate,    watch what happens when you spray ACF50 or Corrosion X on the INSIDE of a wing .  In a couple days there is a 2" circle around each rivet on the OUTSIDE where the  penetrant has crawled through.  Yeah, yeah, I know it's not apples to  apples as water and penetrant have different properties but humid  AIR   CAN and will deposit moisture in those tight places. Seen  it thousands (1000's)of times. If you aren't going to protect ALL faying  surfaces during building, keep them protected with a treatment . I like ACF50  over Corrosion X but it's kinda a Ford -Chevy thing I think. Just use SOMETHING  regular.     John

 [quote]

My question is    though, shouldn't the surfaces that will bear the rivets get the same    treatment.  OR, I had a thought that perhaps the rivet's bearing surfaces    form essentially a gas tight seal with the part underneath, needing no    protection.

 





[b]

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planecrazydld(at)yahoo.co
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Posted: Thu Jun 07, 2007 4:12 pm Post subject: Another Question on Priming

flames on - I have my asbestos suit on.



I believe that all the surfaces you refer to should be primed - mine will be.



I will also be touching a Q-tip with ZPP to the opening in the head of each rivet and wiping with an acetone dampened cloth. The "coated steel" rivet mandrel is bare at the pintail break face.



I bought some of the Cortec primer but I am simply more comfortable with the ZPP so I am not going to use it.



do not archive



dfmoeller <dfmoeller(at)austin.rr.com> wrote:[quote] --> Zenith-List message posted by: "dfmoeller" 



OK.  Here is yet one more question about the black art of priming/corrosion protecting your structure.



I see that Zenith automatically applies CORTEC to interfacial areas on the parts that make up the spars they build.  They do not, however, apply the  protection to the external surfaces of the spars.  By this, I'm referring to the areas where the rivet's heads and tails bear on the aluminum sandwich.



I can certainly see the wisdom of only applying primer to the interfaces between parts rather than the entire parts.  This is where the moisture will wick and cause corrosion.



My question is though, shouldn't the surfaces that will bear the rivets get the same treatment.  OR, I had a thought that perhaps the rivet's bearing surfaces form essentially a gas tight seal with the part underneath, needing no protection.



I realize that my descriptions above may be a little cryptic - sorry.  Another way to describe this would be when riveting part A to part B, I would think one should prime both sides of parts A and B rather than just the interface between A and B because corrosion could start in the interface between the rivet head and A or the interface between B and the rivet tail.  The spars aren't built       Luggage? GPS? Comic books? 

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JohnDRead(at)aol.com
Guest

Posted: Thu Jun 07, 2007 8:09 pm Post subject: Another Question on Priming

Hello All:

             I  was using self etch primers when I started building. Recently I switched to  Cortec 373 thinned three to one with denatured alcohol. This gives the  recommended half mil coating thickness. I brush apply Cortec to all interfaces  on the inside of the structure. I have not decided what to use as a primer when  I get to final painting. The Cortec seems to bond very well without excessive  preparation. I clean of all printed stuff on the parts and all the marking I  have made with denatured alcohol, then a light rub over all surfaces with  Scotchbrite finally a wipe down with denatured alcohol. I let the surfaces dry  thoroughly before priming.

  

 John Read

 CH701 coming along nicely

  



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