Hi All,
A really interesting thread that got me looking a bit deeper, so the Engineer in me comes out; sorry!
Some years back I did a consulting gig at Boeing's paint hangers at Everett
, and learned a bunch about how evil al-clad 2024
[Thanks Wally!] (AKA Duraluminum-tm, your typical aircraft skin aluminium) can be to process and paint so as to provide a long lasting durable clear or pigminted paint finish. Interlux's Pro professional manual covers some of the basics for those who have painted professionally, but can be hard for the average joe to interpret. The data sheets may be greek to many non-pros, and the hazard sheets seem to be written for those with advanced environmental degrees or chemists.
I suggest you all first read the (typical only) recommendations on the Interlux Perfection manual if you are going to use this system, at
http://www.yachtpaint.com/USA/hotlin...n_bulletin.pdf. The section on aluminium starts on page 3 to see what is involved in doing it correctly.
The big problem with all clad aluminium alloys is getting tooth to hold the paint, and cutting through the oxide film to get enough tooth prior to applying a primer, which I feel is a must be used to get any kind of good finish life from any topcoat paint system on aluminium.
Boeing used to buy much of it's skin from Alcoa and others pre-processed and pre-treated with what is essentially a two part complex zinc chromate wash and epoxy etching primer, all applied under controlled factory conditions during manufacture. These sheets have an overcoated plastic for handling during fabrication that is removed at the proper time.
Since we cannot do this in the field, I suggest all wanting paint for themselves should contact either their local Interlux representatives or use the free 800 help line for a specific recommendation on what procedures should be used for our specific alloys on Airstreams in the various climates.
These guys were always great with me in my boat days. Yes, its more work to do it this way, but it will not flake off or otherwise fail if the system method is used. Filling is optional to me, but use the waterproof products, and do not skip steps!!. The best part about marine coating systems for the average joe is roller applications and leveling agents that allow them to lay down like a sprayed finish, but be really careful on vertical surfaces.
Another tip; urethanes are OK over epoxy's, but NOT generally the other way aroundIE no epoxy's over urethanes. I personally think it's a bad practice to mix products between manufacturers unless you know the paint chemistry and the solvents really well, and this information is often proprietary.
2024 or any other copper bearing alloy is never used for marine applications; anyone who had an old Airstream close to the ocean where the original coatings failed can tell you why. Marine alloys that live OK around salt spray on ocean going boats are all of the 5000 series.
I learned all about finishing aluminium years ago by sucessive failures when I did some aircraft restorations; I finally gave up on paint and polished the Luscombe.
Anyone having any more questions feel free to ask; I share nowadays since I went on medicare.
Keep on experimenting, but learn from the Pros.
WLJ
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