New door bottoms

[Jim-ME]

I have recently acquired two new door bottoms. Both have some kind of paint coating on the alluminum. Is this some sort of primer or should I remove it before they get painted?
Jim

[TedW]

That's how mine came. I removed it with thinner before using etching primer. Paint is holding fine.

[Terrys]

If it's a flat black color, that's a primer. Paint sticks to it fine, but it doesn't stick well to the base metal. strip it off and use a good quality etching primer before paint.

[siii8873]

Does everyone use an etching primer when painting? I went to my local dupont paint supplier and asked him what to paint aluminum with. He recommended DuPont 25705 LF Epoxy DTM Primer sealer. And with this I did not need an etch primer. I have used this on all my interior parts before assembly with an color spray of Dupnt Centuri acrylic enamel. It all seems to have adhered well to the parts. I also bought a new outer wing skin that was black. I roughed it up with some sand paper and primed/painted over it. I assumed it was a primer. What do you guys strip this black stuff off with? I've only done the inside of the fender, should I strip the outside before priming / painting?

[Jim-ME]

My doors have a gold or yellow colored coating on the alluminum and black on the steel parts. I guess I'll remove it before painting to be safe. As far as etching primer goes I know ECR uses a PPG epoxy primer. I'm having my parts repainted by a shop that does 18 wheelers and I'm just going to rely on their experience on which type of primer to use.

[Terrys]

Sounds like the aluminum has a zinc chromate primer, which is good. I would make sure the steel frame is well primed, and even after you've finished your paint, pour in some waxoyl into the bottom of the inside. This where the worst of the corrosion starts, Once the frames start rusting near the bottom, it will eventually puch through the aluminum in the winter.

[TedW]

I was told by a "trusted source" that the yellow stuff needs to come off, or at least be washed with thinner before using etching paint (zinc chromate primer works great - most marine stores sell it - it comes usually in green or yellow). Based on my experience the stuff that came on the door wasn't zinc chromate.
The black on the steel is paint - I scuffed it up and then used auto primer on it.
Terry is spot-on regarding the Waxoyl. I treated mine after final painting, spraying it in, sloshing it around so the entire inside of the door frame gets coated, again and again. Then it's a good idea to spray it in the bottom lip where the skin wraps around the steel door frame. Keeps the water out.

At one point Rocky Mountain (of extruded aluminum door top fame) was working on door bottoms with hot-dip galvanized frames, but didn't get beyond the prototype / test run stage. I'll buy 'em if they are as awesome as the door tops.

[jac04]

My doors have a gold or yellow colored coating on the alluminum.....
Is it a coating like paint that can be removed with thinner or stripper? If not, it is probably what is called "conversion coating". Bare aluminum will start to form an oxide layer very quickly. Paint will not stick to the oxide layer. The conversion coating chemically stabilizes the surface of the aluminum and gives the aluminum a goldish hue. If this is the case, do not try to sand it off - just leave it alone.

[junkyddog11]

I've been pulling the skins off doors and galvanizing the frames....the disturbing part is that the brand new door frames are allready rusting underneath the aluminum skin (before the galvanizing)

It's not the easiest thing to do....very time ($$$$) consuming. Doing the same thing with the rear doors, roll up window (defender) doors and also the bonnet frames. Not to mention the pile of fawkin' bulkheads that are consuming one corner of the shop......:eek: