Etch/primer/paint for aluminum panel?

Normally, if you're down to bare metal, an Acetone wash should suffice for pre paint on aluminum.

If you sandblast there's not much need to etch, because both processes are intended for adhesion. Sandblasting can distort metal panels.

If you fine sand it, you might want to etch with a diluted phosphoric etching solution. There are numerous names for it, but it's widely referred to in the U.S. as metal-prep, and is available at most autobody shop suppliers. Make sure you get the instructions for diluting it (normally on the product label), because it's used in different strengths (water ratio) for different metals.

If you don't want to do either of the above, you can strip the panel, carefully clean it with acetone or lacquer thinner, and use an etching primer which is available in spray cans.

Another primer for aluminum and galvanized metals is zinc chromate primer. If you get this product in a spray can, you won't need to use the metal-prep etch, or the etching primer, since it's also intended to applied directly to clean bare metal.

Depending upon which particular primer you use, you'll need to select a finish coat that's compatible with the primer you choose. Generally, all the enamels are compatible as finish coats. Some of the so-called epoxy paints in spray cans might not be, and some lacquer paints might not.

WB ............

Clean, light sand, acid-etch primer, paint within 24 hours. It would be best to use automotive/marine grade polyurethane finish, though good quality spray paint should work well. The key is the acid etch primer designed for aluminum. Any good commercial paint store should be able to help.

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I've been using a spray can of "SELF ETCHING PRIMER" from NAPA. Number on the can is 7220. I let it dry for a while, then use Krylon. No sanding in between. It has worked well for me.

Wayne D.

sand clean [acetone alcohol etc] prime within 15 minutes. Aluminum oxidizes that fast

I found rustoleum baked is harder than krylon

PPG/Ditzler "Alumaprep". It's a phosphoric acid-based aqueous solution, found at auto paint suppliers. It cleans the metal and significantly improves wetting, levelling and adhesion of paint.

Years ago when I was taught to do anodizing on aluminum we used lye as the final surface prep. Unfortunatly I can't remember the solution percentage but IIRC it was pretty week. You might try googeling and see if you can't get a good number.

--.- Dave

A good acid etch after a thorugh cleaning and sanding will give good adhesion for the paint. Oil is your enemy so make sure you have clean paper towels rather than rags to apply the solvent cleaner. Also make sure the bottle of solvent, acetone, mek or such has not been contaminated by someone holding a rag over the opening and turning the bottle upside down to wet the rag, Many paint jobs have come out second best doing this little trick by someone with an oilly rag.

I dont know if you can still get it but zinc chromate is the one i always used. The trick is to put on a real light mist coat and let it dry for at least three or four days before you put your paint on. For magniesium we would let it dry for a week before we painted it.

John

I've got some stuff I bought 20 years ago, and you probably can't get exactly that stuff anymore. There is a 2-part concoction that seems to be a mixture of contact cement and Zinc Chromate. It has a totally noxious solvent odor. And, I know about the cement part because I always get it on my hands, and it peels off just like contact cement.

I sand the aluminum with 240 grit wet or dri sandpaper, but do it wet to prolong the life of the sandpaper. I then wash with water, and then wipe down with rubbing alcohol.

The label on the primer reads "zinc chromate wash primer". The zinc chromate is an anti-corrosion treatment, and probably isn't necessary in my use.

After the primer, I use a "baking enamel" that is only slightly less noxious smelling than the primer. I let the parts dry for a day or so, and then sometimes pre-heat them with a heat gun while still in the fume hood to drive off the last of the solvents before a

This produces a pretty tough coating, but it is not as rugged as a good appliance finish.

Jon

Degrease, irridite (alodine), prime, paint.