To Alodine or not

[Rick S.]

I'm doing paint prep on the airplane and I am using the Sherwin Williams Jetglo line of products. They have been great to deal with by the way, providing pricelists, colorcharts and even an application DVD. Before anyone starts shaking fingers in my face, I've painted several cars and a boat with great results, I'm using a HVLP turbine system with a full face fresh air supplied respirator and my medical eval and fit test are up to date...plus I'm a safety guy by trade no lectures. What I haven't painted is new aluminum. SW has a wash primer recommendation or a conversion coating recommendation aka Alodine. My question is generated by the amazing amount od opinions that say these steps are not needed if you scuff the aluminum and apply an epoxy primer. I just wanted to bouncd this off the forums since I'm sure there is someone with experience in both applications.

[agough277]

As I recall in my paint research Alodine adds to the corrosion protection by eliminating sources of corrosion not protected by paint primers alone. It adds very little to the weight and easy to appy. In some applications I believe Alodine is the only primer needed as in some Dupont products. It will save weight and money. If corrosion is a concern consider using pro seal on all lap joints too, as they do in jets. Mask the joint, apply the pro seal then smooth with you finger after dipping in a detergent solution. It's paintable and makes for a fine seal around the canopy

Al

[Thermos]

Rick,

Alodine followed by a chromated epoxy primer is a "belt and suspenders" approach since both provide corrosion protection. In addition, alodine promotes primer/paint adhesion. But it isn't necessarily a requirement.

My primer (PRC DeSoto's Super Koropon) is supposed to be applied to an alodined surface. But the application notes say if you can't use alodine for some reason, just wet-abrade the surface with a scotchbrite pad, then wash, degrease and clean with Alumiprep. The primer is very tough, and adheres well.

So unless the part is very small and can be alodined with Touch-n-Prep pen, I just use the epoxy primer.

Hope this helps,

Dave

[N8RV]

Rick, it sounds like you don't need any lectures.

Are you by chance using an Axis Citation turbine unit? I'm curious because I bought one years ago at Oshkosh and have only used it to paint my interior. It's OK, but it was a LOT of work getting out the orange peel that I caused.

I'm anxious to hear what others have to say, since I'm getting close to having to do the same thing myself and I don't think the Sherwin-Williams folks around here know anything about painting Alclad aluminum. Good luck!

[chaskuss]

Rick
Alodine does two things.
#1 It improves the adhesion of primer and paint to the aluminum. Paint does not adhere to aluminum like it does to steel or iron.
#2 It inhibits corrosion of the aluminum (at no weight penalty)

If you live in a dry area of the country (and don't plan to ever fly near the coastal areas), you probably don't need to do it. There are other, more EPA friendly alternatives. However, the alternative solutions only improve the adhesion of the primer. They do not offer any corrosion protection.
The reason that Alodine (or it's competitor Iridite) is recommended for use with Mil Spec primers is that the primers only protect from 7 of the 8 types of aluminum corrosion. Alodine (generically called chromate acid conversion process) protects against Filiform corrosion (and 3 other types). Primers do not protect against Filiform corrosion, so for "complete" protection, Alodine and primer are required.
To save weight, some builders Alodine everything, but only prime the interior pieces at the faying surfaces. That's just another way of saying "where pieces connect", like between ribs and skins. Check out the web link below to learn more. See

http://www.eaa1000.av.org/technicl/c...on/corridx.htm

If you decide to Alodine your parts, purchase your chemicals in powder form. This will reduce the expense by about 90%.

Charlie Kuss

[az_gila]

...somewhat migratory IIRC....

Not as in flying South for the winter, but as in moving into any scratches that might occur....

Of course, if your epoxy primer is so tough it won't get any scratches through the paint, then this will have no effect....

[Rick S.]

Originally Posted by N8RV

Are you by chance using an Axis Citation turbine unit? I'm curious because I bought one years ago at Oshkosh and have only used it to paint my interior. It's OK, but it was a LOT of work getting out the orange peel that I caused.

I'm using a rig I picked up made by the now defunt Sprayfine, at least think they are out of business but you can still buy them on ebay. It's a seperate system, one turbine for breathing, one for spraying. I'm not out to start paint wars...The best four points I can give anyone spraying paint are: Contaminate free surface, Proper viscosity (orange peel cause) i.e learn how to use the visco cup and stopwatch, Air Temperature/ Surface temperature/Paint temperature and finally practice. When you can spray a balloon without runs you're ready for the real thing, start with horizontal surface, then vertical, then cylinders and finally the balloon. Triggering and parallel distance from the surface are learned skills. Use a paint pot, saves wear and tear on the arm. That's how I was taught.