[Milsurplus] Painting Aluminum - BC-348 in particular

[swkb4dmf at windstream.net]

---- John Hutchins <olegerityincj at austin.rr.com> wrote: 
> Group  -
> Good evening -
> 
> The black wrinkle tex paint I applied many years ago never cured it 
> remained soft/slightly sticky.  So I am removing the bad paing job and 
> starting over.
> 
> That being said I noticed that there is a green chromate primer layer;  
> Is this a paint or a immersion coating?

John,
  Zinc Chromate paint is available from a retailer called Aircraft Spruce, in spray cans, and they will ship UPS at no additional charge. It just has the usual ORM-D stickers on the box. 
I make replica shock mounts for the ARC-5 and 274N sets so I have quite a bit of experience with wrinkle paint. 
On the subject of cleaning the aluminum:
 The easiest way I have found is to use an aluminum wheel cleaner in a pump spray bottle called DuraGloss 851. It is an etching type cleaner and it works very well. You do have to use it very sparingly on nickel plated stuff, stick to one quick application on things with nickel plated hardware or you'll have copper colored hardware when you're done.
 It's not really necessary to specifically use Drano, a simple Lye and water solution works too. The alloy of the aluminum plays a big role too. 6061 is harder to etch than 5052 or 3003 due to its better corrosion properties but it will etch, it just takes longer. Don't etch until you're ready to prime and do it as soon as possible after etching. I etch, rinse well, blow dry with compressed air, and prime. Aluminum will oxidized very quickly so the sooner you get the zinc chromate on the better. I seem to recall that Zinc Chromate is an etching primer, so the cleaner the aluminum is and the less oxidation you have, the better the adhesion.
The DuraGloss just rinses off with water but I recall reading that the lye solution needed to be first rinsed with white vinegar, then cold water. You may want to research that a little bit cuz it's been a long time since I used that method.
Be very very thorough with your rinse and blow drying, getting all the cleaner and water out of the little nooks and crannies and holes. You don't want to leave any water and especially the cleaner in those places. A front panel is easy, but overlapping riveted parts are tougher.
Painting:
I've tried a lot of different paints but the one that has given me the most consistent results is Krylon brand. It's harder to find than VHT too. The last I bought I had to order from an ACE Hardware warehouse/distributer. Krylon gave them as the vendor for their wrinkle paint products. Before I used Krylon I used the Black wrinkle paint from Harley Davidson. I suspect it was Krylon with a Harley label and a higher price tag because it looked and behaved just like Krylon. :-)
They all will work, but it just seemed like the Krylon best matched the older gear's original texture and like I said before, it gave the same results every time. 
They all say they will wrinkle without heat and maybe they will most of the time, but I've had the same problem you describe when I don't use it. I quit trying it without heat long ago. I use heat lamps in a shop that is separate from the house because it do cause a really big stink!! The other guy wasn't kidding with his line about divorce proceedings. :-) Direct sunlight on a good clear hot day works too.
It takes a while for the wrinkle to appear, maybe 10 minutes tops, but then it spreads over the piece very quickly. Once it wrinkles it's done. More heat or nothing else will change the pattern you get. Set it aside for 24 hours to let it completely dry. 
The wrinkle pattern or texture is determined by three things- Thickness of the coats, how even the coats are, and the time between the coats. For a fine texture use only one coat. The cans instructions should tell you to apply two coats and specify the time between coats. Follow those instructions if you want a heavier texture. What they don't tell you is that wrinkle paint when wet, looks like a very heavy coat, and it is. It seems to go on thicker than most paints look when sprayed. Avoid vertical surfaces if at all possible to prevent runs. It will be a very glossy finish too until it wrinkles. Bottom line, experiment first and keep track of what gave you the texture you wanted. 

Last but not least: Wrinkle paint WILL NOT hide flaws, it will amplify them!! Anything that changes the way that film pulls when it is trying to wrinkle will also change the wrinkle pattern around that change in surface. That means any dent, bump, or even the drilled holes in a panel will have a different wrinkle pattern around them. That tends to make the flaw even more noticeable.

One other ting I've learned from experience is that you can't take a piece from an air conditioned home to a humid outdoors. If you do you have to give time for the moisture to evaporate before you paint. Pay particular attention to that phenomenon when you're about to apply the first coat of primer.

Hopefully this and all the other information from the others will make your next paint job more successful.

Later,
Steve
KB4DMF