Priming aluminum moldings

Doug in NJ

Doug in NJ

Well-known member
I'm getting ready to install the repro aluminum moldings that go around the edge of the roof fabric on my S/W sedan. I was planning to prime them with the same PPG DPLF epoxy primer that I used everywhere else. Should use a special aluminum primer instead? Is there any special metal conditioner for aluminum, that I should apply before priming them? Will the phosphoric-acid based metal treatments work on aluminum as well as steel?

Thanks,

Doug
 
In aviation, aluminium is prepared for painting by using a product called alodine. It is brushed/wiped/sprayed on, and converts the top few microns of aluminium to aluminium chromate. It is left on for about 1 minute then washed off. Don't use it on anything that is installed on the car, the excess that runs of will ruin paint, upholstery and lots of other things. It is a chromate based solution which means it is dangerous for yoursef and the environment. One other thought is go to a boat builder and ask how they prepare aluminium hulls for painting and what paint they use.
 
It turns out that PPG makes a product that probably does the same thing:

DX503: Aluminum Conditioner
DX503 is a chromic acid based chemical that will produce a chrome conversion coating on aluminum and its alloys. The coating formed by DX503 is gold to tan and becomes a part of the aluminum surface. DX503 is medium orange in color and may darken over time.

But it probably runs $20 or so, and an hour or two of my weekday time to go to the PPG dealer and get it. I just don't know if it is worth the cost and trouble...

Doug
 
The DX503 reads to be a similar product, it can be worth it as a converted piece of aluminium has better corrosion protection as well. And $20 is not much when you consider how much the car is worth, how long you will own the car and how much enjoyment you will get from owning and driving the car. The last one is priceless in my view.
 
That's basically my plan. I had installed the fabric last fall, and today I sprayed the last coat of K36 primer. Over the next 3 or 4 weeks, I plan to:

1: Wet-sand the K36
2: Spray a coat of DPLF where the moldings go.
3: Prime the moldings on both sides, with DPLF.
4: Attach the moldings
5: Clean up any excess caulk.
6: Apply a sealer coat of DPLF over the entire car, including the moldings.
7: Apply the finish coat of Concept, naturally including the moldings.

Doug
 
Do not use any black iron [steal] product like phosphoric-acid based metal treatments, unless you wish to dissolve the aluminum.

Alodine, aluminum to aluminum chromate. Or Zinc Chromate as on Palmer Johnson Yachts. Doug has it correct. So do this...
1: Wet-sand the K36
2: Spray a coat of DPLF where the moldings go.
3: Prime the moldings on both sides, with DPLF.
4: Attach the moldings
5: Clean up any excess caulk.
6: Apply a sealer coat of DPLF over the entire car, including the moldings.
7: Apply the finish coat of Concept, naturally including the moldings.

Doug

Perfect Doug.

Yellow stuff. That's Interlux ZINC CHROMATE over the aluminum and the welded seams before the Mexican mudder crew of 100+ slathers on the 'mudd' [Bondo], up to as much as 3 inches to create that fair hull line. A little more than $ one million to paint our 'Beyond Perfection' 150 foot Sport Yachts that sells for about $293,000.00 per foot!

PJBoat3.jpg


PJBoat1.jpg
 
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Doug In NJ ................................
Zinc Chromate ..... skip, from Wisc., mentioned Zinc Chromate. In my business, I painted some outside aluminum window frames, after priming them with Zinc Chromate. That was over twenty five years ago, and it has never peeled. I am SOLD on Zinc Cromate for aluminum !
I tried it on some outside galvenized steel, but it only lasted about ten years, befored it started to peel.
MIKE :)
 
FL&WVMIKE said:
Doug In NJ ................................
Zinc Chromate ..... skip, from Wisc., mentioned Zinc Chromate. In my business, I painted some outside aluminum window frames, after priming them with Zinc Chromate. That was over twenty five years ago, and it has never peeled. I am SOLD on Zinc Cromate for aluminum !
I tried it on some outside galvenized steel, but it only lasted about ten years, befored it started to peel.
MIKE :)
Click to expand...

I wanted to paint an aluminum bicycle wheel and asked a painter what to use. He said be sure to use Zinc Chromate primer. It wasn't easy to find, but I found Pep-Boys and O'Reilly's sells it in a spray can. I can't remember the brand, but it may have been Plasitkote. It sprayed on better than any can of paint I ever used before. I had sandblasted the aluminum wheel to remove the remains of some old paint and corrosion. It's kind of a light olive drab color and sprayed a very thin even coat on the wheel. I highly recommend it.
 
first wash and dry the moldings with mineral spirits. Put on some rubber gloves to prevent oily finger prints on the surfaces. scrub the moldings down with a scotch brite pad and soapy water. Rinse well and dry. I would then apply two coats of 2K etching primer. You can get etching primer in spray cans, it is much less expensive but it doesn't always work as well as the two component etching primer.
 
Thanks to everybody for all the replies.

About spray-can zinc chromate primer: I got the impression that this stuff was too toxic to be sold to the general public in places like Pep Boys or Hone Depot. I have seen Dupli-Color spray-can etching primer in Pep Boys that was light olive-drab color, but I am pretty sure it was not labeled "chromate", and did not have any chromate in it.

I noticed that marine places like West Marine sell a zinc chromate primer. But I took a look at the MSDS for the stuff, and it did not list any chromate compounds:

http://www.easternmarineoutlet.com/index.cfm?fuseaction=product.download&fileId=2042

Possibly they mean "zinc chromate" in the same sense that some zinc-plated repro Model A parts are described as "cadmium plated"? :)

I'm sure 2-component etch primer like DX1791 would work well, but it would probably cost me $50 or $60 for a quart (ten times more than I need).

I can get Alodine from Aircraft Spruce for a reasonable price. So I may just order it from them, unless it has some Hazmat shipping charge that would exceed the actual price.

Doug
 
...outside galvanized steel, but it only lasted about ten years, before it started to peel. The zinc Chrome did not start to peel but rather what was under the primer started to 'let-go'. The self sacrificing hot dip or cold sprayed galvanized coating. It's like painting over butter.

skip.
 
When I need to paint a zinc-plated nut or bolt, first I strip off the zinc with a dip in muriatic acid and parkerize it.

Doug
 
I didn't step in earlier because I thought zinc chromate wasn't readily available any longer. I'd like to know where to get some! With that said, the pics below are part of my tutorial I've posted on installing the center closing front moulding. Note the moulding was prepainted and the paint held up fine from start to finish. The moulding was cleaned/scuffed with a Scotchbrite pad and primed with a spray can of zinc chromate. It was then painted with black Centari. I've done this MANY times and never chipped the paint.

55-b_front_moulding-02.jpg


55-b_front_moulding-06.jpg


55-b_front_moulding-08.jpg


55-b_front_moulding-12.jpg

 
Aircraft Spruce is sending me a quart of Anodine, which is a chromic-acid-based aluminum treatment. I'll probably use 10% of it to do my moldings, but I'll have a lifetime supply for any other small aluminum parts that I mess with in the future.

After reading the MSDS for this stuff, I'm amazed that they can ship it with only an ORM-D hazmat classification...

Doug
 
If I'm feeling lucky I may try painting the moldings first. But the S/W front molding is different than the one in your photos: It has a single relatively thick flap that folds over the part with the nail holes. I am not sure how hard this is to do at the ends of the molding where it meets the drip rails, where it is sharply curved. I think I might need to fold over the flap before nailing down the last few inches of molding, and put one nail at the very end, through a hole drilled through the flap.

The photos you are posted are different than ones from your Tudor roof tutorial, correct? Is it necessary to trim the ends of the molding to the correct length as it is being nailed in place, and touch up the paint afterwards?

Doug

Marco Tahtaras said:
Note the moulding was prepainted and the paint held up fine from start to finish. The moulding was cleaned/scuffed with a Scotchbrite pad and primed with a spray can of zinc chromate. It was then painted with black Centari. I've done this MANY times and never chipped the paint.
Click to expand...
 
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