Restoring Aluminum Prep/Prime/Etc.

[ChampRestorer]

What process are the top shops using on old aluminum? I know about basic etch/alodine/prime with epoxy. Bead Blasting leaves a clean surface, but I don't think you are supposed to blast skins or alclad parts. Is this correct? Or do they etch/scotchbrite? There are reports of paint stripper getting in lap joint and causing corrosion. I have heard of using an etching primer/wash primer to promote paint adhesion. I have tried Dupont Vari Prime and it seems to stick quite well. How do they treat between lap joints without removing rivets. Lots of times corrosion is only between the joints. Is there a process museums use to preserve the aluminum structure without tearing it completely apar? I have always been afraid of etching where the acid could get between a joint that I could not rinse out. Any ideas? Many Thanks, David Johnson, Jasper, GA

[The Inspector]

Try baking soda or dry ice as a media, 100% disapation, no resude and virtually zero impingement on the surface-then dig way, way down in this thread for the primer I posted about alodine nearly two years ago.

[bdk]

Your question is a bit vague, so it is hard to answer.

If there is corrosion, the two ways I know of to remove or treat it is through mechanical means or chemical means.

Corrosion between overlaps can only be truly addressed by separating the offending parts for treatment.

Hopefully the Alclad layer or zinc rich primer has prevented corrosion. In that case you shouldn't need to take anything apart and a simple paint stripping, etch, alodine and paint of the visible areas may be an excellent way to go.

For treatment of corrosion, you may be able to etch the metal at a minimum, or may have to mechanically remove the corrosion, up to and including polishing the corrosion away using caution to ensure that too much material has not been removed. Consult your aircraft specific structural repair manual to learn how much material may be removed.

Paint stripper is thick enough that it should not get between sheets of skin. Cleaning good enough to ensure subsequent paint adhesion should be adequate. Same goes for phosphoric acid etch/brightener and alodine. This is the way it has been done for years.

For simple preservation without removing existing coatings or separating the skin laps there are products like ACF-50 that may be of value.

[Steve Pierce]

I good rinse or even a steam cleaning works well for cleaning out the stripper. I etch and Scotch Brite heavy corrosion, then alodine and epoxy primer.

[bdk]

Yeah, steam cleaning works great with a litle mild detergent. I have a kerosene steam cleaner. Gets everything squeaky clean!

[ChampRestorer]

Thanks for the info guys. David Johnson

[ZRX61]

I have tried Dupont Vari Prime and it seems to stick quite well.

It sticks like sugar to a blanket

The more common name for it is "Yellow Death".. which you'l understand if you ever breathe some of the overspray..

[Kyleb]

David,

Know that Vari-prime is an excellent etching primer, but isn't an epoxy and most solvents will remove it...

[The Inspector]

DeSOTO is one of the manufacturers Boeing uses to provide water based SRF (solvent resistant finish) primer. It's usually a 70 Baracuda 'Grass Green' shade (there is another fuel cell primer but it's a different I.D. BMS 10-20 and is used inside JET fuel tanks) but, being water based and comercially avalable, your local well stocked commercial auto paint supplier should be able to A) obtain it and B) tint it to whatever tone or shade you need. It sprays evenly and lays down semi matt and skydrol impervious after a few hours setup time, cleans up with tap water so after priming, just fill your paint cup with hot water and blast away to clean.
Remember to abrade the finish away when making an electrical bond for best conductive path, and reapply to the area after the bond assembly is done. It ain't cheap, but it's my experience that the only thing cheap in aviation is the hourly wage-