If you’re familiar with the VansAirforce “Primer Wars” you know this is a highly debated topic among RV builders. First, lets cover some background information you’ll need to know.
The vast majority of the airplane is made out of alclad aluminum sheets. These sheets are an aluminum alloy with a very thin layer of pure aluminum that gets bonded to the the top and bottom surfaces. You get the strength of the aluminum alloy combined with the corrosion protection of pure aluminum. What a deal!
Corrosion depends heavily on the environment. Near a coast or salt water body the corrosion is going to be more aggressive than if it was in a dry environment. Let alone, what if you scratch a part? What if you scratch through that pure aluminum? That corrosion protection is now gone! Sure there’s ways to prevent and fix that, but it would be easier to not worry about in the first place. I’m a bit of a cluts some times, and knowing that I may some day live in California or the wet state of Minnesota, I’m going to prime.
There’s two main groups of primers, epoxy based and non-epoxy based. The non-epoxy based primers are wash primers, rattle can primers, think light thin coats. The epoxy primers are exactly what they sound like, they get sprayed on and form a hard shell on the material. Epoxy primers are going to be a little heavier but also will provide better knick/ding protection as well as very good corrosion protection. The group of non-epoxy primers are a thin light coat that through chemical etching binds and coats the aluminum. Epoxy primers are also slightly more expensive that non-epoxy.
What will I do?
The best option for me is to go with P60G2. I definitely want some extra protection, but I’m not building this aircraft to last 50+ years. AKZO is nice, but you pay for the weight every time you fly. There’s a good thread here from VAF that shows the corrosion resistance of P60G2, and demonstrates why Van’s themselves use it on their quickbuild kits.
My process will be this (version 1).
- Cleco and drill to final size.
- Debur all sides and holes.
- Clean with Bon Ami and water.
- Scuff with 3M’s maroon (although gray might be better) Scotch-brite and a light layer of Bon Ami.
- Water should turn light and milky.
- Aluminum will turn to dull finish and water should sheet off of it.
- Rinse with water and let dry.
- Spray a light coat of primer with a Harbor Freight Purple HVLP gun.
- 1 part P60G2, 2 parts R7K44.
- Gun pressure 30psi.
- 2 light bidirectional coats. Will darken as it dries.
- Dry for 24+ hours.
- Assemble and Cleco.