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Old 03-24-2008, 07:10 PM   #15
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Painting Aluminium

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 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.

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Old 03-24-2008, 07:44 PM   #16
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Hi All,
One quick repost before I get skewered by the knowlegable! When working with any coating systems nowadays, it is essential - no MANDANTORY to preserve your life and the lives of others around you to FIRST read, understand, and follow implicitedly all of the required supplier instructions, precautions and to use ALL of the required protective equipment specified by the suppliers.

The chemistry of many of the two part coating systems contain cyanates which can kill dead quickly, turning you into an instant corpse at the worse or do you much more bodily damage that is a whole lost worse than drinking bad "shine" (methanol,AKA wood alky or rocket fuel by my Southern relatives).

Also, DO NOT try alternate solvents or substitute any others unless you want to visit your dead relatives before it is your turn. That means you too, Bubba.

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Old 03-31-2008, 05:45 AM   #17
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I think it is important to point out the early Airstreams used "Alclad" aluminum. Alclad is made from a core of 2024 aluminum and is protected from exterior corrosion by a cladding it with pure aluminum which forms a dull protective oxide finish. If you use straight 2024 it will deteriorate rapidly when exposed to salt sea air. If you want to keep the Alclad pretty you will need to protect it with a clear protective UV resistant paint. Airstream had a material they tradenamed "Plasticoat" made for them. The formulations have changed over the years. They had found that automotive grade clear coats were to hard and brittle and that is why they formulated a special paint.

History of Aluminum at Airstream

1947 Heat-treatable copper-alloyed 24ST. Side and end panel sheets were 0.032 inches think supplied by
Kaiser Aluminum. Metal could be heat-treated to be as strong as mild steel. Material had high-purity Aluminum cladding rolled on one side that made it brighter and more corrosion-resistant.

1960s Alcoa became the supplier of choice. Same grade of aluminum now called Alclad 2024-T3.

1970s (early) Experimented using 6061-T6 aluminum, a less expensive heat-treatable grade.

1970s (late) Alcoa supplied 3004-H18 Brite panels, 0.032“ thick.

1983-1993 Alcoa supplied a “Controlled Mill Finish” in a 3003-H18 and 3005-H18 grade – lower cost material in place of heat-treated aluminum.

1993-1994 Airstream widened the body, requiring stronger aluminum for the weight. Side and end panels remained 3003 or 3004-H18 but thickness increased to 0.040 “.

12-22-1992 to 7-31-95
Alumax coating: Serial Numbers 509137 through 510640; 7-31-95 1996 Model

7-31-95 to 1/1997
Alumax ends with trailer #510640 and we switched to Yenkin-Majestic as Plasticoat supplier. Used and
sold to dealers until it was pulled on 1-1997

1-1997 Airstream switched to Akzo as Plasticoat supplier.

1998 Airstream started using Alcoa pre-coated metal:
Partial start in 1998; currently still use.
Exceptions: Serial numbers
512502 all Alcoa except seg#25 out of Alumax 8-7-1998
512503 all out of Alumax
512504/505/506 all Alcoa except seg#25 out of Alumax
512507 all out of Alumax
512508 all Alcoa except seg#25 out of Alumax
512509 all out of Alumax
512510 all Alcoa except seg#25 out of Alumax
512511 all out of Alumax
512512/514/516/518/520/521/522 all Alcoa except seg#25 out of Alumax
512524 start 27FT trailers and longer all out of Alcoa 8-19-1998
512613 begin all units are Alcoa 9-8-1998.

5-1999 We started using llow voc plastic by Akzo –still currently in use.

Note: 6063-T5 grade aluminum –corrosion-resistant. With simple heat treatment, 6063-T5 is as strong as mild steel. Currently used for extrusion and ribs.
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Old 03-31-2008, 06:31 AM   #18
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I realize I'm a bit late into this thread, but yes, painting the roof white does cut down on the exact issues that have been described.

Airstream paints the roof white and if you've noticed newer school busses lately, they too seem to have started to paint the roof white as well. I can assure you that they all don't do it because it saves any time or money.
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Old 03-31-2008, 07:29 AM   #19
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Originally Posted by scottanlily
I know inland andy had done some good tests with aluminum panel samples painting them three different colors and the for one was plain aluminum .I don't know the link,but someone here might or contact andy himself at inland rv.The surprise was that the aluminum plain sample was cooler than even the white one by a small but surprising amount .The plain sample just reflected the heat away better the test revealed .I would check into that before I would paint the roof of your airstream .I myself thought the white would be cooler .Scott
I tried to get the same kind of data last year, but missed the hot weather by the time I got serious. I did discover, however, that moderately polished aluminum is 20 degrees cooler in bright sun than lightly corroded aluminum, documented here:

There will be further tests done this summer and posted here:
Once the aluminum panels are tested under the sun, I'm going to do comparitive tests where the outside and inside of the outside panel are painted white (high reflectance and low emissivity should help on both sides).


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