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Tibbo's RV-14 Hobby
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Date: 12-31-2016
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Number of Hours: 6.00
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Manual Reference:
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Brief Description: Priming preparation
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Priming. It's what keeps a surface from rusting when exposed to the gaseous corrosive known as oxygen. For iron, rust is red and is known as iron oxide. This type of rust flakes off and progressively damages the surface in layers until it's all dust. Rust progression in this manner can take weeks to months.
When aluminum rusts, it forms a clear, super-hard layer and then stops rusting; its rust is known as aluminum oxide. Unlike iron oxide, aluminum oxide is harder than aluminum (closer to diamond actually) and also has a higher melting point. Aluminum surface when freshly scratched will form aluminum oxide within a few hours. Most skins and some other pieces are marked as "AlClad" meaning it's been clad with pure aluminum on the surface to intentionally harden it (via oxidation) to protect the underlying structure of aluminum alloy. This surface is thin, however. If the surface irregularly rusts, it could degrade the strength of the overall surface.
When my first EAA technical advisor checked out my work, he said it was good, gave me a few tips, then told me that every year on his plane he has to do corrosion prevention on some skin parts. Every year he does this. He told me if he were just starting over, that he'd prime everything on the inside, because the AlClad isn't quite thick enough to last several years at a time.
I decided to start over, and here I am again. Scrubbing new parts and getting them ready to prime at the free carwash of my apartment complex. I scrubbed the parts with a soapy industrial solution called "PreKote", and srcrub the metal with an aluminum oxide pad between 180-400 grit to remove any AlClad and aluminum oxide on the surface. The PreKote helps tremendously with this, and also provides a layer that assists in primer adhesion. This residual layer temporarily protects the surface, and allows me to spray primer within 24 hours of scrubbing.
The process is simple enough: Apply PreKote, scrub all surfaces working into a rich lather, and don't let anything dry. Add more PreKote
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Carwash Carport
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Scrubbed out skin of VS. I have one more scrub pass to make on this.
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Horizontal Spar. Yes, the sun set while out here. It was a lot of manual labor.
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