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Thread: Refinishing Aircraft Paint

  1. #1

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    Refinishing Aircraft Paint

    I assembled this checklist from a lot of different sources, and interviews, after I could not find anything online here that covers it. Please let me know your thoughts and suggestions.

    Assumptions: You are using chemicals per the chemical manufacturer’s safety and handling instructions.
    DuPont Technical Page Sherwin-Williams

    Remove the paint:
    1. Thoroughly wash the plane with a wax free soap, especially landing gear and other areas which may have grease or oil residue. This will improve the performance of the strippers.
    2. Remove:
      • Control surfaces
      • Inspection panels
      • Fairings
      • Moldings
      • Bag and mark the fasteners so you know which type went where later- even if you are replacing them. I like to take cell phone photos of everything during disassembly.
    3. Cover windows with aluminum foil and edge with foil tape. Extend the foil tape 3/8” past covered area onto the metal airframe. This edge will be stripped separately later.
    Also cover with foil and foil tape:
    • Plastic, Fiberglass and composite (not removed in step 2)
    • Boots
    • Antennas
    • All openings into aircraft such as door seams (¾ inch aluminum foil tape). Can’t emphasize this enough – you don’t want stripper inside your airplane which will work its way out later so even cover small openings including where the inspection panels were removed.
    • Thin strips over the wing/fuselage gasket (Piper).
    1. Wet the shop floor and cover with plastic polyethylene drop cloths ( if compatible with your choice of stripper) - so you can recover waste. Apply the stripper and cover with polyethylene drop cloths ( if compatible with your stripper) to prevent it drying out early - the polyethylene can make the stripper last indefinitely depending how well you seal it. After checking a test spot, scrub paint loose with stiff 12”-14” broom, re-apply more stripper, then pressure wash – don’t spare time or water on this step. Don’t use too narrow a pressure washer orifice - it will be easy to damage thin components.
    2. Remove remaining paint and corrosion from the following parts:
      • Rivet lines
      • Seams
      • All edges that were covered with the foil tape.
      • Important – do not use steel wire brushes or scrapers because the steel particles will embed in the aluminum promoting corrosion. You can use non-steel abrasive pads.
    3. Perform Airframe inspection by A&P for corrosion or underlying damage to aircraft.
    Treat the metal:
    1. Acid Etch process with an aluminum cleaner to guarantee that all residue has been removed (Dupont 13204S or 13205S as examples) and rinse with water. (From Bill Berson) 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.
    2. Alodine (chromic acid) is applied (such as DuPont 13206S Aluminum Conversion Coating solution) , left on until color change is evident, and rinsed off with fresh water and then dry overnight. (Note - you must not let the Alodine dry on the plane)
    3. Dupont recommends priming as soon as possible after this coating as been applied, no more than 36 hours or it should be reapplied.
    4. Wear plastic gloves from this point forward if you haven’t already; oil from your skin is bad for paint adhesion.
    5. Perform Airframe inspection by A&P.
    Fix problems:
    1. Clean plane with MEK or similar.
    2. Mask as necessary with paper and masking tape. Mask any opening – blowing paint into the wing is sloppy.
    3. Wet down the floor to eliminate possible air contamination caused by paint technician movement across the floor during the paint process.
    4. Coat with epoxy primer to provide corrosion resistance and paint adhesion. The paint must be applied soon or the primer must be lightly sanded. Check paint manufacturer specs. Sherwin-Williams recommends a minimum setup time of 12 hours before top coat is applied and a maximum of 36 hours. After that scuffing is required for paint adhesion.
    5. Sand fiberglass/plastic panels removed or masked earlier – anything not stripped. I like to finish with 400 and then 600 grit wet paper by hand after 220 machine sanding.
    6. Use body filler to fill small blemishes in the airframe, sand smooth. Check out Sherwin Williams Fill Bond
    7. Apply fill primer (sandable high-build epoxy primer such as SW CM0560566) as needed and sparingly - mask off panels not needing fill primer.
    8. Sand fill primer coat - again with 400 and then 600 grit wet paper by hand after 220 machine sanding.
    Paint:
    1. Once you begin, from this point forward, the clock is ticking. Steps 2 – 8 should be done in the same working day for best results.
    2. Primer was applied minimum 12 hours prior and no more than 36 or scuffing is required. Check primer/paint data sheets.
    3. Clean plane thoroughly. Sanding dust blown out of small pockets has ruined many paint jobs.
    4. Mask as necessary with paper and masking tape. Mask any opening – blowing paint into the wing is sloppy.
    5. Wet down the floor to eliminate possible air contamination caused by paint technician movement across the floor during the paint process.
    6. Coat with two coats of high gloss polyurethane. Start with the lower surfaces of the plane and work up.
    7. Color stripes are added after appropriate drying time, but not too long after. Check paint manufacturer specs.
    8. Remove tape as soon as possible while the edges are still soft. Leaving it too long can imprint paint below (for striping) and could tear/chip paint edges when removed.
    9. Reassemble control surfaces, cowling, etc. with new stainless steel screws as appropriate – consider nylon backing washers where possible. Avoid painting any fastener that will be frequently removed such as cowl fasteners.
    10. Factory-designated equipment and specifications are used to balance all control surfaces by A&P.
    11. Inspect your aircraft, and make logbook entries.
    12. Replace existing placards with new placards in accordance with FAA requirements.
    Last edited by PurpleZL1; 07-09-2012 at 02:51 PM. Reason: changed order of events added Berson comments

  2. #2

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    That's quite a detailed checklist, here is my single comment:

    I never used any fill primer on a metal airplane yet, seems to me just added weight and cost. But if you do use fill primer (what is it?) then shouldn't it go on top of the epoxy coat to smooth the epoxy? The epoxy primer should be the first coat.

  3. #3

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    Thanks - That's why I posted the checklist. I found the fill primer note on a painter's website. They used high solids sandable primer in areas needing work such as hail dents and followed it up after the work with the epoxy primer just before painting. I noticed Dupont recommends full primer coats right after the Alodine and they also recommend no more than 36 hours between painting the epoxy primer the color coats. That would mean you would need to work really quick or face sanding the epoxy primer after the 36 hour mark.

  4. #4

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    All of the paint manufacturers instruct that after the primer is applied, the paint should be applied within a time limit or you need to sand for best adhesion.

    Best of luck,

    Wes
    N78PS

  5. #5

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    Thanks - I updated the post - in blue - moving the epoxy primer to be applied first to the entire plane and then a sandable primer over that (per Sherwin-Williams) in areas that need it. I have some very light hail dents so I will probably apply the sandable primer to the top of my wing and some body filler.

    Anyone know where we can buy commercial aircraft stripper? I heard "Aircraft" strippers have corrosion control properties not found in other strippers.

  6. #6

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    Aircraft stripper - I think that I have seen it at Pep Boys. Your local auto paint supplier will likely stock it. Airplanes and custom autos are really the applications for a quality paint remover. I will note that I am told that not all brands of stripper are effective with all types of paint. I think that I read that Sherwin-Williams might actually make a really good stripper that attacks polyurethane effectively.

    The paint stripper that you find in Home Depot and Lowes is really targetted at furniture refinishers and applications like metal house trim items.

    If you are removing the paint from an entire airplane, be aware of the environmental concerns. I understand that there are now paint removers that are environmentally friendly, but I do not have experience with them. What you do not want is to have your hangar designated a sire requiring formal environmental cleanup.

    Best of luck,

    Wes
    N78PS

  7. #7

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    Actually the strippers found in retail stores are not ideal for large projects like this. PPG has a product called Eldorado PR-2002, and there are many others, but I can't find anyone who will sell them to an individual - so far. I have stripped several vehicles with retail products and they are too much work.

  8. #8

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    Quote Originally Posted by PurpleZL1 View Post
    - Anyone know where we can buy commercial aircraft stripper? I heard "Aircraft" strippers have corrosion control properties not found in other strippers.
    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.

  9. #9

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    Purple,

    I think someone gave you some bad info. Your checklist is filled with instructions for a disaster. Below is a list of things I see that are disasters looking for a place to happen. There is no such thing as “painters plastic”, at least not in regards to painting an airplane.

    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. A broom will not scrub the softened paint off. Use a plastic bondo spreader, or a small piece of aluminum sheet. You CAN use a steel wide blade putty knife. Just don’t press into the aluminum very hard.

    At one point you mention what Dupont recommends for priming. Later you mention Sherwin Williams. It is best to decide what brand you are going to use and follow that manufacturer’s recommendations and directions. What works for one brand may not work for another.

    If you have hail dents, fill them with body filler and after sanding it smooth, THEN put sandable primer over it. Don't but body filler on top of primer.

    You mention that the color stripes are added when the paint has cured for a certain time. It is best to paint the color stripes FIRST. After that paint is dry, you mask it off and shoot the rest of the plane. Then when you remove the masking over the stripe color and there is your stripe.

    You also mention removing tapes as soon as possible while the paint is still soft. This will lead to a very ragged edge. It is best to let the paint dry thoroughly before removing the tape. About 24 hours is usually a good time. Spend the money for 3M "Fine Line" tape.


    Before you spend many hundreds of dollars on stripper and make a big mess, get some 280 or 320 grit "wet or dry" sand paper. Fill a bucket with water and see how quickly you can water sand a one foot square down to the aluminum. Don't sand over rivets unless they are counter sunk. Notice how long it takes you to do a one foot square. Then use stripper to do a one foot square. Include in the time for the stripper the amount of time you spend cleaning the shop floor and power washing the stripper out of the seams on your plane. Make sure you keep the hangar well ventilated when using the stripper.

  10. #10

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    Thanks Pearson - I think the plastic drops cloth will depend on which stripper you use? Most of my information was gleaned from various paint shop sites, all who say they use newer EPA friendly chemicals - noted most showing the process without a mask. Good point - I will update the list to check compatibility.

    Bondo over bare aluminum? Would like more clarification on that, I would think there should be something under the bondo to prevent corrosion? I painted a few trucks when I was a kid and it was not unusual to find corrosion under old bondo on the aluminum cabs. It looks like commercial shop practice is to not sand aluminum skin and since it's pretty thin to start with that may be why.

    Stripe painting before or after is probably a personal call. If you paint them first, you must deal with dust over the greater part of the plane while the stripes dry. Again, on the commercial sites they almost universally paint the plane white, wait (per the label instructions) tape, and paint stripes.



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