February 4, 2007

Priming the HS Parts - 2.0 Hrs.

Today I cleaned, prepped and primed all the parts for the HS.

Speaking of priming, there seems to be an endless debate among builders about priming aluminum aircraft parts. In fact, it's a subject that has come to be known as the "primer wars" because there's so much discussion and disagreement about it in the online forums, among builder groups, etc. It's not only a matter of deciding which primer to use, but how to prepare the surface before using it, and even whether to use it at all! Many of the parts, as they come from Vans, have an alclad surface. This is a very thin layer of pure aluminum laid down over the alloy that the part is made of. The alclad very quickly oxidizes to form a tough durable aluminum oxide coating that's actually quite resistant to corrosion. Because of this, many builders don't prime at all. I chose to, though. I live in the wet rainy Pacific Northwest and I plan on flying my airplane over to the coast when I'm finished. If you've spent any time there, you know how hard the salt air is on ANYTHING left in it for any time at all. So my parts will be primed. Even when not near the coast, though, wetness and damp air lead to more risk as far as I'm concerned. So for me, the choice was narrowed down to which primer to use, and the prep work involved. Rather than spend too many hours agonizing over this and doing research, I just followed the path that my technical counselor, Randy Lervold, has chosen. Rather than repeat his work, I'll just let you refer to it if you wish. Here's a link to his discussion and method for priming: Randy's Priming method.

So following in his footsteps, the product I'm using is SEM Self-Etching Primer. One big advantage is that it's available locally at certain auto parts stores. So I can go get more whenever I need it, without paying shipping and waiting for a delivery. It comes in 3 colors; black, green, and gray. Gray is actually my favorite, but they didn't have any in stock, so my first can will be the green color. These parts won't be seen, so it doesn't really matter if I change colors later.

I took everything outside and spread a piece of plastic over my patio picnic table. It was dark when I finished spraying everything, but here they are.

Other builders were right. Using a sharpie to mark the parts works out perfectly well. It bleeds through the primer and clearly shows up when you're finished. As soon as these are dry, I'll be able to rivet things together. I can't wait!

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