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There are several questions about livery changes and livery in general on this website. Yet, I fail to find information about paint removal.

As a routine maintenance for an airframe that can live for up to 30 years, livery is redone several time as explained here. When changing painting, it should be preferable to remove the old one (I'm mostly thinking about weight as a big airliners has a lot a surface to paint). Moreover, I imagine that for military aircraft changing their operation theater, paint must be redone to adapt camouflage, and thus accumulating many layers of paint may have consequences.

Given material and other aviation-specific constraints, I also imagine there are special techniques to handle any intervention on the airframe.

Is this paint removal done and if so, how?

chicks
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Manu H
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  • I know tanks and other ground vehicles get new camo jobs, but I don't think aircraft do, do they? The air is the same color in either case. –  Sep 11 '19 at 17:17
  • Tangentially related: https://aviation.stackexchange.com/questions/14500/why-is-most-aircraft-livery-painted-rather-than-vinyled – user3067860 Sep 11 '19 at 18:38
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    @Hosch250, the air may be the same color, but the ground isn't, and military airplanes tend to spend most of their time on or very close to the ground. – Mark Sep 11 '19 at 22:36
  • I think they typically land pretty far behind the fighting line--some planes are only based out of the US midwest and do round-trips--notably spy and bombers. They are painted to provide camouflage/mind tricks in combat (which way is the plane actually oriented, am I looking at the top or bottom) etc. Maybe I'll post my own question about this, though. –  Sep 12 '19 at 17:53
  • @Hosch250 See this one: What is the dark spot visible below the cockpit on A-10s? – PerlDuck Sep 12 '19 at 18:07
  • I did. I think that's a standard paint job, though. –  Sep 12 '19 at 18:22
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    @Hosch250 The US midwest is, proportionally, only a very small part of the world. – Lightness Races in Orbit Sep 13 '19 at 11:17

4 Answers4

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Paint stripper. Lots of paint stripper. (originally I said thinner, but I have been corrected, it's more accurately called stripper)

Seriously though, it's actually not too different to other things that you paint. You need to spray on paint stripper. But, just like when painting the aircraft, it's imperative that you cover up all the delicate systems on the aircraft fuselage.

See here:

Also, I think it would be rare to paint a new livery over and existing one without first removing the old paint (maybe only if you were just changing small details), because covering an aircraft in paint weighs A LOT. For a 747 or 777 sized aircraft the paint job can weigh over 1000lbs

Carrying that around costs fuel and fuel costs a lot!

Simon Opit
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    Welcome to Aviation.SE! Nice first contribution, I hope you stick around. – AEhere supports Monica Sep 11 '19 at 08:09
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    When my plane was repainted in fall in 2018, paint stripper was used. Hydrogen peroxide based, it took everything off. http://www.crossroadsfencing.com/airplane/painting%20pics/IMG_0200.JPG After sitting overnight, the plane is rinsed and the wastewater collected in barrels to be shipped off and processed somehow. Some areas needed a 2nd application to get down to bare aluminum http://www.crossroadsfencing.com/airplane/painting%20pics/IMG_0202.JPG – CrossRoads Sep 11 '19 at 12:13
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    What is paint thinner? Organic solvent? What is it in particular (or just some examples) - compounds? Are there special ones for aircraft? – Peter Mortensen Sep 11 '19 at 14:12
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    Paint thinner is mineral spirits (Stoddard solvent) which may have been washed, i.e. recycled. Paint stripper is an organic solvent mixed with wax to slow evaporation; the solvent penetrates the paint and causes bubbling as it evaporates lifting the paint. Methylene chloride and NMP are common. The stripper in the video is a combination of solvent and caustic compounds such as lye that actually dissolve cured paint. You won't find them at the local hardware store because they also dissolve the lignum in wood, but they are sold to shipyards, and I assume, aircraft painters. – Matthew Gauthier Sep 11 '19 at 15:37
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    Paint thinner doesn't make paint melt off like that. The video says "thinner", but that's not what's happening. As Matthew points out, it's some type of paint stripper. Just waned to reiterate that it is not just thinner. Answer should be edited. – JPhi1618 Sep 11 '19 at 15:59
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    If I had to guess the stuff they are using in that video is called, "Aircraft Stripper". IN cycling, if you paint your frame, you can remove baked on coatings with it as well. For a consumer, you can buy small jugs, of it. It's basically a corrosive chemical that bubbles the paint off.

    Example: http://www.kleanstrip.com/product/aircraft-paint-remover

     – knocked loose Sep 11 '19 at 19:04
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    It's not paint thinner. Aircraft paint that,s applied in proper facilities like this is usually LPU / Imron or other 2-part works-like-epoxy coating. Not least, because it's thinnest and lightest. These dramatically transform into long polymers, so they are immune to their own solvent even 1 day into curing. They are probably immune to retail "Aircraft Remover" too, but there are solvents that will attack them (and not aluminum, that's the real trick). – Harper - Reinstate Monica Sep 11 '19 at 19:43
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    Stoddard solvent is a mild case of a paint thinner. More serious ones: Acetone, Nitrocellulose thinner, Methyl-Ethyl Ketone (MEK), Stabilised Tetrahydrofurane (THF).... – rackandboneman Sep 11 '19 at 20:13
  • "it's actually not too different to other things that you paint." Except the paint used is very nasty stuff. – Mast Sep 12 '19 at 08:14
  • Mine was painted with a Polyurethane. Really durable stuff. Gas, Oil, Stoddard Solvent do not touch it. I don't know about it's nastiness. http://annexpaint.com/index.php?main_page=product_info&products_id=111 "DuPont Imron Industrial Strength® is the next generation of Imron technology. Based upon patented DuPont formulations and resin technology, Imron® Industrial Strength is the fastest Imron yet, providing the "Wet Look that Lasts" with the lowest environmental impact. Imron Industrial Strength can be purchased in Gloss, Semi gloss, Satin or Flat." – CrossRoads Sep 12 '19 at 11:55
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    fuel costs a lot [citation needed]. For all its wonderful properties (huge energy density, liquid in standard atmosphereric conditions, "freely" available in the ground) petroleum is actually dirt cheap. Try to power a 777 with fuel cells or li-ion batteries. First, see if it's possible at all. Then, take a look at how much it would cost. – Eric Duminil Sep 13 '19 at 09:29
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    Eric, I feel you've missed the point entirely. I didn't say jet fuel does not have currently unbeatable energy density, I said it costs a lot. Which it does. It's the single largest operating cost for airlines. Here's a citation: https://www.iata.org/whatwedo/Documents/economics/Airline_Labour_Cost_Share_Feb2010.pdf – Simon Opit Sep 14 '19 at 00:23
  • Commercial airlines burn 100 billion gallons of fuel every year. I do hope it's a large operating cost for them. And it's not because fuel costs a lot, but quite simply because they burn 150 000 olympic swimming pools every year. – Eric Duminil Sep 14 '19 at 09:33
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    Ok, I guess we'll have to agree to disagree on how we determine what is a high cost item for airlines. But when you need to pay for a operating cost that can increase in price like this, just today, I believe it's a high cost item. I'll happily accept, there is currently no other technology available that could provide a better solution. – Simon Opit Sep 15 '19 at 22:19
  • 1000 lbs? Why do they bother painting them at all then? (other than the company logo) – user253751 Aug 13 '21 at 12:26
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In addition to the chemical method in Simon's answer, there are mechanical methods, like bead blasting. This method was introduced in the 80s by airforces concerned with the volume of chemical waste generated by their maintenance facilities.

It essentially consists of using compressed air to project fine plastic particles against the painted part at high speed. These abrade the paint away mechanically and can be recycled a few times before they break down too much and become ineffective. Glass particles can also be used for more heavy duty blasting, but these need more careful procedures to avoid damaging the substrate, since they are much harder than plastic.

Abrasive blasting not only removes paint, but also dirt, corrosion and even anodic coatings, with enough passes.

Whether it has any advantages over chemical stripping, depends on the specific case. Industry regulations change across time and space, and waste plastic dust might be more problematic than waste chemicals in some places, but not others. Also, the size of the parts to be stripped and the kind of training required for the operators play a significant role in choosing one method over another.

AEhere supports Monica
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Not to be a smart-ass, but I think the correct answer is "in accordance with the airframe manufacturer's instructions."

Aircraft are generally given a corrosion protective layer (or passivated) at the time of manufacture that usually gives them a green color before they are painted. For this reason, unpainted planes are sometimes called "green" planes. Historically the treatment was usually a zinc chromate primer, but that is highly toxic and I doubt anybody still uses it on new planes. I suspect some of the more modern treatments add green pigments just to give the green planes the expected look, but I don't actually know that.

Following manufacturer instruction on whether and how to use chemical strippers or mechanical removal of paint is important to not damage the protective layer in ways not expected by the manufacturer. Some treatments require parts to be dipped in a chemical bath before assembly, so if you remove or damage that treatment layer, you're not likely to be able to restore the corrosion protection to an as-new status. If you remove the protection and replace it with your own in a way not specifically approved by the manufacturer, your plane no longer is in full compliance with the type certificate and you've become something of a test pilot.

TL;DR: Don't do stuff to planes that isn't approved by the manufacturer or a supplemental type certificate applicable to your specific plane.

DCP123
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    Stripped planes are taken down to bare aluminim. The AL is then washed, acid etched (something like a mild vinegar), alodyne applied, then primer (the green color), then paint. The stripper doesn't know to stop at the primer level. This was mine after the alodyne stage, before primer http://www.crossroadsfencing.com/airplane/painting%20pics/IMG_0311.JPG – CrossRoads Sep 12 '19 at 11:59
  • @CrossRoads Reminds me of a DeLorean :-) but I'm afraid it lacks the Flux Capacitor. – PerlDuck Sep 12 '19 at 17:46
  • Well, that and stainless steel :) – CrossRoads Sep 12 '19 at 18:52
  • Yes, @CrossRoads, but the look is awesome! – PerlDuck Sep 12 '19 at 18:57
  • The green layer is just a temporary protection that gets stripped before the aircraft is painted. – fooot Sep 16 '19 at 15:20
  • I appreciate people sharing their experience with ways (some) planes are stripped, but you still only repaint aircraft in ways approved by the manufacturer. I've done work for a manufacturer that feels quite strongly that the treatment on its planes should not be removed by stripper and that, because stripper doesn't know when to stop, the paint on its planes should only be removed mechanically. Maybe you can get equivalent protection, but when you modify an aircraft in a way contrary to manufacturer instructions and don't have an STC, you don't really have a properly certified aircraft. – DCP123 Sep 18 '19 at 16:28
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There are other methods in addition to the chemical and mechanical ones already mentioned in other answers. In some cases, paint is removed from aircraft using a laser.

Here's a video I found from the US Air Force that demonstrates the process:

Robin
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    F16, 25 hours for 2 robots. C130, 75 hours for 4 robots. Bet a Cessna would be pricey, if one could get time at an AF base to have it done. – CrossRoads Sep 12 '19 at 16:14