Primer for aluminum

[Pierre Hulin]

I have just bought skins for my stabilator at Webco. The parts are not primed. I would like to prime these parts before fitting and painting to eliminate the risk of corrosion. Please let me know the reference of a good primer dedicated for aluminum. Spruce aircraft sells alodine 1201. What do you think about?

Regards
Pierre

[Charles Schefer]

I think zinc chromate is the normal primer. It's an olive drab green color. That's what I use though I bum it off the jet mechanics in our hangar when I need it and most of the stuff I've used is a slightly darker shade of green than the factory green.

- Charles

[Zach Grant L1011jock]

Alodine first, then prime, then paint. Zinc primer is old school and works. Newer tech is epoxy primer. Dont just paint bare aluminum. It wont stick, will look terrible, and will eventually corrode...

[Kristin Winter]

Alodine 1201 is a treatment for the metal. Normally used after Alumiprep 33 is used to clean the metal. After that, zinc chromate or two-part epoxy is the best primer and corrosion preventative coating.

[Charles Schefer]

Zach / Kristen - As usual I learned something from your posts, thanks. However I just looked up Alumiprep 33 on the Aircraft Spruce website and it defines the product use as "Use to clean, brighten and transform badly corroded aluminum to its natural appearance.". So... given that would this need to be used all the time before painting or only if the metal is corroded?

I also looked up Alodine 1201 on Spruce and it says: "After precleaning with Alumiprep 33 or Metal Prep 79, rinse with water. Apply Alodine without dilution by brushing or swabbing with sponge. Rinse with water and surface is ready for paint. This is a visible coating which leaves the surface with a golden coloration.The alodized surface provides protection against weather and firmly bonds paint. 1 quart treats about 100 sq. ft. Flammable. Available in quart and gallon sized."

Metal Prep 79 the write-up says: "METALPREP 79 is a non-flammable multi-purpose phosphoric acid based cleaner and prepaint conditioner for most metals.

METALPREP 79 cleaning and conditioning chemical leaves the surface chemically clean and corrosion free.

METALPREP 79 can be used to deep clean and etch a metal surface prior to paint or to prepare a surface for a subsequent chemical coating like that produced by GALVAPREP® SG on zinc and steel or ALODINE® 1201 on aluminum surfaces. Chemical coatings offer the best affordable substrate for both paint adhesion and underpaint corrosion resistance."

So maybe Metalprep 79 for aluminum in good shape or Alumiprep 33 for corroded metal? then follow with the Alodine 1201 then paint?

- Charles

[Kristin Winter]

I have always used the Alumiprep as that is what the Alodine process called for. Is Metal Prep 79 made by the same company as Alodine? You can probably locate the manufacturer online and download the instructions for Alodine. That would be the most definitive and safer than relaying on Spruce's copy writers.

[bernard nowlen]

acid etch( muratic acid deluted with h2o) alodyne, prime(zinc chromate or an epoxy such as in Bostic BMS 211( a boing product we used on sea planes) then paint. Both spruces preps are basic a muratic acid delutetd with h2o. I used this process on a seabee restoration and all worked fine. bernie

[Charles Schefer]

[David Pfeffer]

Bernie is correct. AlumiPrep is just a brand named acid etch. I use it as well personally, but we use a genaric acid etch on our military aircraft. One thing to add- you'll almost always have to scuff the surface with a good scotchbrite pad prior to chem conversion coating with the Alodine to ensure it's retained. My process for metal sheet:

1. Scuff with scotchbrite
2. Etch
3. Alodine
4. Prime

Chromate epoxy primer is the absolute best. We've spent hundreds and thousands in labs to come to that conclusion (corrosion is a HUGE cost in Naval aviation). MIL-PRF-23377 is fantastic stuff.

Also, be sure the CLAD side of the sheet is on the outside (exposed) surface if you purchased Alcad sheet.