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Dave White RV-7 Build Site
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Date: 4-24-2011
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Number of Hours: 3.25
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Manual Reference:
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Brief Description: Priming - still not cracked it :-(
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Well, today I tried to remove variables in order to determine why my spray painting is often unsuccessful. Tim, a professional aircraft repair and maintenance chap, kindly offered me the use of his workshop and airline setup to remove my own spraybooth from the equation - or to confirm that as the problem.
The pictures show the issue: In the first photo (of the rudder spar), the right hand side of the picture shows metal with some fairly decent paint whilst on the left you can see that the paint finish is atrocious. It just isn't adhering properly, and for the full horror see the second image. :-(
I don't understand it. It would appear that there's some contamination on the metal, preventing the paint from sticking. Both Tim and another local engineer both said "silicon" when they saw it, but if so, I can't see where the silicon - or any other - contamination is coming from. The metal parts are protected for as long as possible in the blue plastic covering in which Van's supplies them. Then, once the covering comes off, I have taken to wearing disposable gloves to prevent the oils and grease from my skin getting onto the metal. I use Scotchbrite to remove the Alclad and give a rougher surface for the paint to key onto, then immediately prior to spraying I degrease the part with a liberal application of acetone. I let that dry off, helping with heat if necessary, then spray paint - making sure it is properly mixed before it goes into the gun.
It *should* work...
Anyway, I sprayed all the rudder parts today at Tim's place, and they were mostly OK except for the rudder spar, which was still awful despite another Scotchbrite blitz and acetone wash. So, I went to town again before the new paint had dried and took as much old and new primer off as I could, using a Scotchbrite pad soaked in acetone. This took the part as far back to bare metal as I could, and I've just sprayed it again.
We'll see how it looks once it has dried overnight.
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Paint OK on the right, no good on the left
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The full horror. Surface contamination?
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Dry that air supply! Tim's setup.
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