I pulled this off a alum boat paint site.
How To Paint Aluminum
Maybe you have an old aluminum boat that you would like to repaint. Aluminum cannot be painted directly. It must first have a conversion coat applied, and then the conversion coat can be painted with any paint that is formulated for application on metal.
You have probably seen many instances of aluminum with peeling paint. This paint was applied by someone who either did not know this, or didn’t care. A terrible waste of energy and money.
Sanding the aluminum makes no difference. It must have a conversion coat applied if you want the paint to stick.
The first thing that should be done, is to remove any scratches or gouges in the aluminum by sanding these smooth with 180 grit or finer sandpaper.
Next the aluminum should be thoroughly cleaned with soap and water. After it is dry, it should be cleaned with a grease removing solvent such as enamel or lacquer thinner. Wipe this solvent on, and then wipe it off with a different cloth or paper towel (several towels).
When this is dry, wipe the entire surface with a tack rag that has been completely unfolded, to remove any dust particles. Turn the tack rag over several times to obtain a different surface of the rag as you wipe the aluminum down.
The conversion coat that works best on aluminum is called Vinyl Wash Primer. This is available from several different paint manufacturers such as Martin-Seynourâ„¢, Cook Paintâ„¢, Sherwin-Williamsâ„¢, NAPA, and others.
Vinyl wash primer uses a catalyst-thinner that is usually mixed at a ratio of two parts catalyst to one part vinyl wash primer. So remember to purchase twice as much catalyst as vinyl wash primer.
This product is available in quarts, gallons, five gallon cans, and 55 gallon drums. You don’t need more than a quart unless you are painting a B-52 airplane (which might take 5 gallons).
Read and follow all manufacturers Warnings about this product. It has been known to cause cancer in California rats (so have cigarettes). (label says: "Known by the state of California, to cause cancer in laboratory rats")
So you must wear a respirator when spraying this product or lighting up, especially in California.
Spraying Vinyl Wash Primer
Spray one wet coat of vinyl wash primer over the entire area of the aluminum using smooth, even, same-speed strokes. Overlap the spray strokes a couple of inches as you spray. Do not miss any spots.
Do not be concerned that the surface of the aluminum is not changing color by much. Just make sure the primer shines wet as you spray. The vinyl wash primer will darken a little when it dries. The aluminum will have either a greenish or yellowish tint when it dries. This is correct.
Caution
Over application of vinyl wash primer will cause it to peel
One transparent coat of vinyl wash primer is plenty of material for the conversion coat. Do not empty left-over material back in the can that it came from. This will ruin the material in the can. Dispose of any remaining material properly in accordance with environmental regulations (or spray it on something else).
This conversion coat will dry quickly, usually in about 15 minutes. You have 24 hours to coat it with something else. I recommend a couple of coats of epoxy primer for a superior coating.
Epoxy primer is another two part, California rat killing, product. This product is available in most automotive paint stores. I recommend two coats of this epoxy primer be applied using the spraying technique mentioned before. Once again, read and follow all label instructions and warnings.
