Mustang said:
Guys,
I'm interested in something that could be used over a completed wing. We will be getting our QB wings and fuselage soon, and I wanted to do something to promote adhesion after the outside surfaces have been cleaned up from the oily stuff they use for shipping the parts back to the states from the Phillipines.
It is my understanding that alodine cannot be used to treat the riveted outside surfaces, correct?? Obviously one would not use the Alumiprep for sure, picture the acid running into the rivet dimples and soaking into the rivet crevices!!! Yikes!
Well, what about this Sanchem stuff. Can it be used on the wings after they are built?? I will be using Super Koropon epoxy primer before topcoating, but I want to promote adhesion to this previously oily surface if possible.
Thanks,
Pete
It's best if you don't touch the outside surfaces with any chemical or primer until you're ready to paint; period. You gain nothing and only make more work for yourself later when it IS time to paint.
While you are building, lot's of people will come by to visit you and touch and feel and drool over the airplane parts ("Build it, and they will come"), and you yourself will be handling and crawling over (and drooling on
) parts of it as well.
None of that will hurt anything and will all come off when you start cleaning and prepping the surface metal for the paint process that will come many, many, many (did I say many?) months down the road.
I agree about the sloshy mess when doing the Metalprep/Alodine procedure. During all those years while I was in the business, I never did like the idea of how the various liquids could wick into hidden places.
Part of the process involves really thorough cleaning that requires physically wiping or Scotchbriting areas before and during the procedure, and there are simply some areas you can't physically get to. It is just those hidden areas where corrosion is most likely to develop. And you are very astute to note that the pre-treatment, acidic chemicals that will CAUSE corrosion, can get into places that make it difficult to properly flush out.
Still, that's basically how it's done which is why I've always looked for a better way.
But I digress...
You're getting way ahead of the game by even talking about painting since you don't yet have your QB parts yet, but just to give you something to obsess about (like many do with regard to this subject
), I'll throw some stuff at you:
My opinion, and this is just my opinion so I welcome anyone else who considers themselves knowledgeable on the subject to chime in, I will personally NOT put up with the mess of Alodine (process) on the outside surfaces because if you are going to do it RIGHT, you ARE going to be taking a chemical bath yourself in the process. It's just plain messy, and review my previous comment about bad stuff getting into hidden places.
I like the 6100 because it's a lot "cleaner" to apply correctly than Alodine, so my intent for the outside finish on my RV is to start with 6100, then go right into a seal coat with DP/LF epoxy primer, then the following day, I'm right into painting.
However, another really good option that would work equally as well for long term durability and protection is, after thoroughly cleaning the bare aluminum with wax and grease solvent, go right into spraying a basecoat of PPG 1791/1792 primer.
That's a very good corrosion resistant primer that, as a primer sprayed on
properly cleaned bare aluminum, will offer corrosion protection equal to a metal treatment. Since the 1791/1792 is a true "self etching" primer, it DOES react chemically with the aluminum for the purpose of both corrosion resistance AND adhesion.
As an aside, note that as good as epoxy primers are, they do not "react" chemically with the aluminum. They simply protect, and stick, and promote "sticktion" to what's applied over them, incredibly well because of the physical properties of catalyzed epoxy primers.
Using 1791/1792 means that you don't use any metal conversion pretreatment at all, because it is IMPORTANT to note that when using 1791/1792, the PPG P-sheet for the product says very specifically that
"If applying DX1791 to clean, bare metal substrates metal treatments are NOT REQUIRED OR ADVISABLE."
If you're one of those guys who wants to pick up a spray gun and just "get going", this would be a proper way to do it, and the best way to think of using this product is to realize that it simply REPLACES the metal conversion process of Alodine or 6100. After the 1791/1792 is sprayed, you would then spray the DP/LF epoxy primer over it, and then go right into the topcoat paint.
If you think you want to be "safe" by putting 1791/1792 on top of aluminum that you have already treated with ANY kind of metal conditioner like 6100 or Alodine, you'd really be screwing up. Since the 1791/1792 was DESIGNED to be a self-etching primer, it NEEDS bare aluminum to react with, so it would be counter productive to put a barrier between it and the aluminum (i.e., the Alodine or 6100) that would prevent the 1791/1792 from working as it's designed.
One of the reasons why this subject is so never-ending and confusing is because there is no one, exactly correct way to do it. There are several different ways, and they are all good, but once you pick your process, you have to follow it through and stay with all the chemicals and paint that are designed to be compatable with the other parts of the same process.
Changing in the middle, or combining processes (like putting 1791/1792 over aluminum treated previously with a metal conditioner) will cause you lot's of problems.
My personal experiences are mostly with PPG products and I stay with that family of paint products because they make a coating that will paint just about anything.
I have no doubt that Super Koropon is just as good an epoxy based primer as any other high quality brand, but be careful about
mixing brands because brand families are designed to be chemically compatable with other products in the same brand. If you use Super Koropon, I'd highly suggest that you stay with the other DeSoto paint products for the rest of the paint process.
DeSoto mentions in their P-sheet (about the Koropon) that it doesn't have to be top coated. However, that's exactly the "feature" I was talking about when I described about how, if the PPG DP/LF epoxy primer is allowed to cure beyond one week, it becomes a "top coat" (for interior use only) by default if not recoated by then.
Speaking of that, note that DeSoto mentions over and over in their Koropon P-sheet that it is an "interior" primer so they are making it clear that the Koropon doesn't have to be topcoated, but ONLY if it's left un-topcoated as an INTERIOR coating which should sound familiar with respect to what I've been saying about the PPG epoxy primer and how it should only be left unpainted if it's used in an interior application.
What all that tells me is that the Korpon and PPG DP/LF are identical products used for the same applications in their respective families of products.
Vern
RV7-A