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Thread: Refinishing Aircraft Paint

  1. #11

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    In my airplane paint shop, we always put the bondo on bare aluminum (no primer but after alodined). Mostly because it is the fastest and easiest way for a production shop. Otherwise the sanding will go through primer anyway and need more work.
    The finished bondo area could use some extra spot primer coats first, then prime the whole thing.

    When young, I worked in an airplane paint shop that never used primer at all, just etched and alodined the stripped aluminum and coated directly with white Imron paint. This saves weight, cost, time, and is much smoother than primer. Makes it easier to strip later also. A working commercial plane gets scratched more than corrodes on the external skin and a new paint job every 5 years is needed anyway. Maybe 10 years, if treated well.
    I think only float planes need primer, but it is your call.

  2. #12

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    If I understand correctly, the traditional acid etch and alodine process can be environmentally problematical. Modern paint manufacturers specify a self-etching primer for best paint adhesion. Ease of future stripping is a negative attribute, not a positive one. Modern paints are supposed to be hard to take off....

    Best of luck,

    Wes
    N78PS

  3. #13

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    The phosphoric acid etch improves paint adhesion by cleaning away oil. It should be applied with a weed sprayer and scrubbed well with scotchbrite. This is the most important step in paint adhesion because the acid scrub and rinse removes the oil/wax. Beaded water indicates oil, keep scrubbing with etch until the water flows flat. This is called the water break test in the composite industry (works for paint adhesion also) The self-etch primer without acid scrub will not provide this.
    Skip the alodine if you can't deal with the waste disposal and consider the self- etch primer. But don't skip the phosphoric acid. I don't think phosphoric acid is harmful to the environment.

    Lear Jets need more adhesion than a Sonex. The more coats, the more stripper required to remove. Again, it's your call, but I guarantee the paint salesman will insist you go with the most expensive process.

  4. #14

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    Strippers

    Quote Originally Posted by martymayes View Post
    Turco makes a full line of aviation stripper/coating poducts. Methylene chloride, low odor and water based, just name yur poison. They have epoxy stippers, polyurethane strippers, stippers for aluminum, magnesuim, etc. They also make alkaline cleaners for cleaning the stripper off and getting the grime out of wheel wells and engine compartments. If you want one stop shopping you can buy your alodyne, conversion coatings, corrosion removers, etc. from the same Turco dealer. You can buy all that online at Graco or equivalent but watch out for hazmat shipping. I'd try and find a local dealer.

    FWIW, anyone can put goop in a bottle and call it "aircraft stripper" ....doesn't mean it's a product you should use on your plane.
    Some strippers: (will five gallons do a Cherokee 140 with only one very thin paint job?)
    • EFS-2500 by Molecular-Tech Coatings in Canada and distributed here by Graco - in stock. It runs about $280 for five gallons and sample not available.
    • Oxystrip 2030 Pro by General Chemical is $32.25 a gallon, water based, and I have ordered a quart to test. Less expensive, but it may take more.
    • SPC-909 by AkzoNobel looks promising. Graco $362 for five gallons. Non-stock and 4 weeks.
    • Turco 5351 is the old Methylene chloride paint stripper and it's $403 and non-stock at Graco.
    Also,
    • PPG only sells to pros apparently.
    After I get some samples I will do some tests and report back with photos.


    Updated 7/16/12

    Dad's Easy Spray Contractor Grade. I tried the regular Dad's last weekend alongside the Oxystrip and while the Oxystrip had no odor and seems to be skin friendly it was slow and difficult to keep mixed. The Dad's is thin enough to spray with a garden pumper (Viton required) but thickens on contact and takes the paint off pretty good. I just noticed they make a "contractor grade" of the same stuff and I will try that as soon as the order arrives.

    In this picture the white was already scraped off with a plastic tool and the red, which was a stripe over the white, needed more time. The plastic kept the stripper wet indefinitely - or at least for a couple of hours. I took off about 10 sq. ft. of paint with a quart.

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    Last edited by PurpleZL1; 07-16-2012 at 12:43 PM. Reason: Added updated info

  5. #15

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    Amount of stripper depends on the paint type and thickness and skill of worker. Many Cherokees were factory coated with lacquer. This will melt rather than lift, and worse, water makes it solid again. So additional coats of stripper work best without water, try to squeegee it off before using water for the last bits.

    Most singles need about 20-30 gallons, I seem to recall. It all depends.

  6. #16

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    This one was stripped and painted at a shop in Alabama in 2003. There are chipped areas all over the place and the white paint is faded. I bought it in 2008 and the paint was trashed then (I keep it inside) but the paint comes off so easy I figure the stripper will have an easy time. It's a shame the $10,000 paint job didn't last any longer than it did.

  7. #17

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    I see you have confirmed my comment that a paint job usually lasts about 5 years (2003-2008 in your case).
    It hardly helps to spend $10,000, in my opinion.

    Proper surface cleaning is most important (post #13) and should make the paint last 10 years. But even Imron will have fading and some cracks at 10 years. Airplanes flex. Not much can be done other than repaint.

  8. #18

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    If you use Imron to paint your airplane, you will be lucky if it stays attached for five years. Imron is very brittle. I would never use it to paint an airplane. Air Tech Coatings and Polyfiber both make a great urethane paint that will flex. Because it is flexible, it doesn't flake off like a more brittle paint. Of the two, I prefer Air Tech Coatings because it seems to flow out better. The Poly Fiber is great, but I seem to get more orange peel with it than the Air Tech Coatings finish.

    If you are doing a plane as small as a Cherokee 140, I would just water sand it down rather than mess with chemical strippers. You can use a scotch brite bad over the rivets. It is almost as quick as chemical stripping and much quicker clean up. It is also cheaper.

  9. #19

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    Uh, properly applied Imron is NOT brittle. I have one airplane that was painted with Imron in the early '80's that still looks great and is not chipped. I have another airplane that was painted with Imron in the early '90's and also still looks great despite being parked outside in New England for most of its life. I don't baby the airplanes either.

    If your paint is only lasting 5 years you need to patronize a better shop.

    Sanding the finish off an airplane is an exercise for a real masochist. I have sanded a lot of paint and it helps keep my upper body in shape. If you don't have lots of spare time and need "wax on - wax off" to be part of your conditioning and weight loss program, I recommend a good chemical stripper to remove your paint.

    Preparation is everything with paint, so once you have the airplane stripped, do spend a lot of quality time with a good cleaner, scotchbrite, and a good self-etching primer. And follow the directions for the paint exactly as printed.

    Best of luck,

    Wes

  10. #20

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    When in doubt - TEST

    Quote Originally Posted by Pearson View Post
    If you cover your shop floor with plastic sheet, the stripper will drip down onto it and make a huge mess when it melts the plastic. I am not sure why you would cover the windows with “painters plastic” and then cover that with aluminum foil. Just use aluminum foil.
    If you cover the stripper with plastic drop cloths, it will melt the plastic into a gooey mess.
    In ASA's Airframe Volume 1: Structures, by Dale Crane (which I believe anyone working on their own airplane should read - big help to me anyway), on page 212: ".. apply a heavy coat of stripper with a bristle brush or a nonatomizing spray, and cover it with polyethylene sheeting to prevent it evaporating before it does it work."

    What you said made sense to me because this stuff is so caustic and a long time ago I literally melted a tail light on a car with paint stripper. However, it appears polyethylene plastic does not mind the stripper at all. To test this I poured hardware store stripper into a polyethylene sandwich bag and left it overnight - no problems - see pic below.
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