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Evan
11-18-2004, 02:01 AM
Has anyone used two part zinc chromate etch wash primer as a prepaint primer treatment for aluminum? I priced some out today, bloody expensive but the guy tells me it is superior to ordinary zinc chromate primer for paint adhesion. Aside from the cost the pot life is really short, about 1 1/2 hours.

This is something I never ran into in the aircraft biz. Must be new or something (in the last 30 years).

shapeaholic
11-18-2004, 09:19 AM
Evan:
I have used this stuff a couple of times when I painted a/c for a living. It's OK but as you say it's expensive.
In my opinion it is primarily used to eliminate a couple of the steps needed to get good adhesion in industries where the aluminum is not moving more than 100mph, and it is only as good as the surface preparation.

Regular zinc cromate primer is also a thing of the past.(carcinogen)
Most a/c manufactures use a two part epoxy type primer on top of one (or sometimes two) primary treatments.

Depending on what it is you are going to finish, I would suggest the tried and true; wash part well with a detergent like "tide" and maroon scotch brite, rinse well with copious quantities of clean water, etch with phosporic acid, rinse with even more water, treat with "alodine" and rinse with water, let dry. You will know if the part is clean if the alodine creates an even coloured surface and the wash water flows off without beading up.

Use an epoxy primer and the topcoat of your choice (I like Dupont Imron)
All of the above material is available at your local Dupont paint dealer, although they sometimes call the items different names.

I've painted a lot of a/c in my 30 years in the industry and havn't had the paint come off one yet.

Cheers
Pete

Involute
11-18-2004, 09:37 AM
shapeaholic- This may be a stupid question, but... when painting a/c, are you alodining the whole plane?

coles-webb
11-18-2004, 10:52 PM
When I primed a Cessna 172 I Alodined the whole plane first.

Involute
11-19-2004, 11:28 PM
Thanks, I'm familiar with alodining smaller parts - I just never considered doing the whole plane. Don't really know why... it makes sense, though.

shapeaholic
11-21-2004, 11:59 AM
Involute:
Sorry for the delay in responding, I was out of town.
As Cole-webb says you do alodine the whole airplane. We used to mix alodine powder in a garden sprayer of water and apply it in a fine spray. This had two benifits, 1) alodine got applied as economically as practical, 2) it allowed us to see any spots where the water beaded on the surface. This would indicate a dirty spot. If the water didn't "sheet" you would have problems with adhesion, and the paint flaking off.

Pete

Don Clement
11-21-2004, 12:15 PM
I use DuPont Variprime (615S with 616S converter) on aluminum when unable to anodize. This is a self-etching primer. See http://www.dupont.com/virginia/front/front_make.html

Don Clement
Running Springs, California