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To self-etch or not to self-etch

zsadecki

Active Member
If using some pre-primer treatment (like Alodine, PreKote, SanChem) does mean that you shouldn't use a self-etching primer? Is the non-etching 2 part epoxy primer (like AKZO) less 'nasty' then the self-etching stuff (since it doesn't have the acid in it)?

I think my plan is to use PreKote and AKZO to do all the internal structure. So, is there any place to buy the AKZO (or is there another good alternative?) other than spruce? I've read that it can be found for $65-70, but I can't find it. Only at spruce for $110.
 
The way self-etching primers work is by reacting chemically directly with the aluminum. Any pre-prep such as Alodine, Sanchem, etc., becomes a barrier to the self-etching primer so they won't work the way they are supposed to.
In fact, you may very well lose some adhesion qualities if you do that.

Think of it this way; you decide up front if you want to use a pre-prep system (Alodine etc.) OR you use a self-etching primer. It's one OR the other.

Either way, once you've done whichever you decide upon, you'll follow up with an epoxy based primer as an adhesion promoting sealer before going right into your color. Epoxy primers are not self-etching primers.
Vern
RV7-A
 
If you read the DuPont Technical Manual for their 225S Acidic Cleaner (Alumiprep) and 226S Conversion Coating (Alodine), you will find that DuPont VeriPrime Self-Etching Primer is among the primers recommended for use on aluminum surfaces that have been prepared with the 225S/226S Aluminum Finishing System.

I believe that the acid in the primer acts to etch not only pure aluminum surfaces, but stable oxide surfaces as well, and thereby creates some "tooth" for better mechanical adhesion of the primer.

That's how I'm doing it, anyway.
 
You have to not only read the P-sheets carefully, but also make sure that what you're reading is the "Official" p-sheet for the product.

For the 225, this is the p-sheet:
http://www.performancecoating.dupont.com/dpc/en/us/html/prodinfo/chromasystem/H-19290_225S.pdf

For the 226, this is the p-sheet: http://www.performancecoating.dupon...prodinfo/chromasystemlv/H-19393_226S_Alum.pdf

For Variprime, this is the p-sheet:
http://www.performancecoating.dupont.com/dpc/en/us/html/prodinfo/chromasystem/H-19303_615S.pdf

Maybe I didn't read close enough, but I couldn't find any mention of where Variprime is "recommended" for use directly over either the 225 or 226 treatment. (Logically, however, and in my mind, I don't see why using Variprime over JUST the 225 "etching" chemical would hurt anything, but I sure wouldn't use it over the 226; that might cause problems. Still, I wouldn't do EITHER, and for no other reason than that Dupont didn't say that I could ;) )

The only "substrate" shown and approved under the Variprime in the Variprime p-sheet is:
"Substrates: Properly prepared/cleaned steel, aluminum and galvanized."

Without going any further, I personally take that to mean "bare metal" that has been cleaned of contaminants. However, for further clarification as to what specifically means "proper preparation", the very next paragraph in the p-sheet says:
"Surface Preparation
Wipe surface with DuPont First Klean 3900S™ or Prep-Sol® 3919S™.
Sand and featheredge with P180 DA grit paper followed by P240 DA grit.
Remove sanding residue with DuPont 3939S™ Lacquer and Enamel Cleaner, DuPont Final Klean 3901S™ or DuPont Kwik Clean 3949S™."

All of those are just degreaser chemicals and sanding... no metal pre-treatment at all.

Please don't think I'm trying to start a p****** match with what might seem to be nitpicky details. It's just that I've been bitten hard by overlooking teeny little details in how products work together and I'm hoping to let my mistakes, oops, I mean "experience" help others.

Will doing what you are result in paint peeling off in sheets a few months after it's painting?... I don't know; probably not.
But you might find that adhesion might suffer a little from spraying the Variprime over the 226, and it might appear that leading edge surfaces will chip a bit more easily that you would like (from thrown up rocks and sand abrasion).

There's enough that can go wrong in the paint process when you do things exactly right without pushing one's luck by going outside the intended use of manufacturers products.
Speaking of going wrong when you do things right, and as an example... I have a vivid recollection of a Corvette I painted years ago where some of the paint prep was done about 50 feet away from where a car was being detailed for delivery to a customer.
No one noticed the newly hired helper grab a bottle of ArmorAll and spray it quite liberally over the tires on the car he was cleaning. I won't go into the gory details of how spray silicon that drifts onto a car (yes, 50 feet away!) just before painting makes things really interesting.
Let's just say it ain't pretty.

Thanks for bringing up yet another memory that makes me happy that I'm doing something else for a living now. :D

Highflight
RV7-A
 
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Interesting. The Alodine data sheet you provided a link to is from the DuPont Low VOC ChromaSystem Technical Manual dated 10/02, while the sheet I was referring to is from the ChromaSystemTechnical Manual dated 06/02, which I downloaded from the DuPont site.

Why the difference in recommended primers? Your data sheet is for Low VOC products. Could it be because VeriPrime isn't LowVOC?

In either case, both data sheets say that DuPont 226S chemicaly stabilizes aluminum, producing a high degree of corrosion resistance and adhesion for paint systems. I don't think adhesion will suffer from its use. I would exoect it to be improved.
 
Dave Cole said:
In either case, both data sheets say that DuPont 226S chemicaly stabilizes aluminum, producing a high degree of corrosion resistance and adhesion for paint systems. I don't think adhesion will suffer from its use. I would exoect it to be improved.

You're absolutely correct that adhesion will not suffer between the base aluminum and the 226S. And you also correctly use the phrase "paint system". However, 225/226 and Variprime are parts of DIFFERENT paint "systems".

What I would be concerned with is the adhesion you can expect between the Variprime and the 226S. While it's possible that the adhesion between those two products may not suffer, I can very much guarantee that the adhesion between epoxy primer over the 226S would give you a lot better adhesion than Variprime over 226S. (I'm talking long-term durability here).

Keep in mind that the 225/226 "process" and the Variprime "process" are two totally different ways of achieving virtually the same result. Mixing the two processes doesn't mean that you will get the benefit of both combined.

Like any system, it's the "weakest link" that will fail, which is why I get so retentive about not only basic compatability between products, but also really nitpicky that I make sure that each of the products within a system are used exactly as they are intended and in the context of what "system" they are intended for.

Highflight
RV7-A
 
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to self-etch or not to self-etch

ppg aerospace manufacture De Soto Aerospace Coatings.

Sterling Chemical Coatings (Sterling Lacquer MFG.CO.) manufacture paint systems for aerospace and marine have look at their web site


don
 
A quick note about Vari-Prime. Most any solvent will wipe it off. Funny thing is, paint stripper has little or no effect on it. Also, if you paint over it, any time after it dries you can split the primer with a razor blade. You can remove the paint and it will have primer on the back of the flakes and the skin will still be primed.

Personally, I don't like Vari-Prime but as always YMWV.
 
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