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Prepping for primer

SabreFlyr

Well Known Member
Sponsor
I have been having the local maintenance shop prime my interior parts. They use Super Koropon and I've been very satisfied with the results. Originally, one of the maintenance techs was doing the painting and he was my metal work and painting guru...until he was killed in a very tragic accident. Based on guidance from a mechanic who used to work in our hangar, I had been prepping my parts by scuffing them lightly with Scotch-Brite and then wiping with MEK. After a while, I forgot to do that last step, or quit for some reason I don't recall. Since the accident, the only techs in the shop with any painting experience are a couple of avionics techs who are very busy, but one of them is a friend (who happens to drive an RV-6).

I was talking the other day with another mechanic in our company hangar. When I told him that I usually scuffed my parts for priming, he asked why. My presumption was that it was to aid in adhesion but I had to admit that I didn't know. He didn't think that there could be any good reason to do that. He believed that the proper prep was a dip in alodine and then spraying the Super Koropon. Since then, I checked with my friend to see just what they did. They clean the parts with DuPont Centari 8022S reducer and then spray. They don't use any AlumiPrep or alodine.

Now, mind you, it's becoming a mute point how I prep my parts because I have so few parts remaining. The interior bulkheads for my -14 tail cone are already primed and only the tail cone skins, stiffeners and longerons remain. Then I'm on to the QB fuselage and QB wings.

So, let me say first of all that I'm not asking if they're cleaning or spraying my parts correctly. I'm satisfied that the parts are, at the very least, adequately protected. My only question is whether there is any good reason to scuff the parts or wipe them with a solvent such as MEK.
 
Prep

I believe so. At least the scuffing. It provides some mechanical adhesion. The paint adheres better to the rough surface. Personally, I don't believe solvents do much. The idea is to remove the aluminum oxide layer just before painting. Paint doesn't stick to it very well. It's only a few microns thick so if the scuff is timed right, it would remove it. Problem is it reacts quickly and reforms in hours. Some of us us powdered cleanser and scotchbrite just before paint.
 
Ahh, then my scuffing is definitely not well timed. The last batch were waiting in the shop at least a month before they could find time to get them done. The avionics shop has been getting their butts kicked by a couple of STec digital autopilot installations. I can't believe they're not all bald by now! Sounds like I need to go to plan B where I spray my parts in their paint room, which they have offered to let me do. Thus I could scuff and head straight for the spray booth.
 
Clean

Ahh, then my scuffing is definitely not well timed. The last batch were waiting in the shop at least a month before they could find time to get them done. The avionics shop has been getting their butts kicked by a couple of STec digital autopilot installations. I can't believe they're not all bald by now! Sounds like I need to go to plan B where I spray my parts in their paint room, which they have offered to let me do. Thus I could scuff and head straight for the spray booth.

The scuffed parts would need some sort of cleaning. A wash dry and wipe with a solvent would work. If parts are scuffed with a cleanser like Bon Ami then a thorough rinse followed by dry and wipe would suffice. Basically, wipe off any oils or debris with a lint free cloth and some sort of cleaner designed to remove oils. Shoot as soon as possible.
 
Super Koropon is an excellent primer, but like all coatings should be applied according to the manufacturer's recommendations for best results (ie. adhesion and corrosion protection).

Super Koropon surface prep states:
Super Koropon? 515-700 primer can be applied over clean properly prepared aluminum and composite surfaces. Aluminum surfaces shall be treated with materials conforming to MIL-C-5541 or equivalent.

http://www.ppgaerospace.com/getmedi...d_Resistant_Interior_Primer.pdf.aspx?ext=.pdf

Henkel Alodine conforms to this MIL-C-5541. Preparation for Alodine is via Alumiprep 33. All of my parts were scuffed with Scotchbrite and Alumiprep 33 prior to the Alodine.

None of the other surface preparation methods (MEK, BonAmi, gunwash) meet MIL-C-5541 so the adhesion of the Super Koropon cannot be guaranteed.
 
Well, as I mentioned, it's pretty much mute at this point. Of course, I should have confirmed earlier that the shop was prepping my parts according to PPG's guidance. But, that's water under the bridge.
 
Man, I really hate to tell you this, but your great-grandchildren are never going to forgive your memory for having to re-prime a couple of spots in the hidden areas of the plane you left their grandparents.
 
Scrub

The trouble I see with not scuffing is if there are contaminants on the surface. I scrub with scotchbrite not for better adhesion mainly, but to remove the silicone contaminants and stuff. Getting better adhesion is a plus. But I am using the Sherwin Williams P60G and it warns to not sand blast parts because there are not enough solids to fill in, so I dont scuff too aggressively.
I will let you know if this is the best method... in about 15 years.
 
Man, I really hate to tell you this, but your great-grandchildren are never going to forgive your memory for having to re-prime a couple of spots in the hidden areas of the plane you left their grandparents.

Thanks for the smile! :) Also helps to keep things in perspective.

And, John, thanks for your input. Good thoughts.
 
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