Well, isn’t building a Fastkkit RV like cheating, too?
Of course – cheaters !!! 
Even a quick built is way more work than one can possible anticipate when never having tried it. But painting is one of those things that is really frustrating. If you ask 100 professionals or builders you get 100 different answers. If you read in books you get the one answer you don’t want and that is:
The “correct” and “only” way to treat 2024 alclad for aircraft use is to scrub it with Scotch-Brite in running water until the surface is water break free (a smooth film everywhere). Then the surface is etched 1-2 minutes with acid solution, always wet and rinsed with clean water. Then Alodine (or similar) on the surface and kept wet for 5 minutes and rinsed with water. When this is done, a epoxy primer must be used. On top of that goes Poly Urethane top coat. Everything has to be “aircraft quality”, or your airplane will fall down from the skies due to unknown effects when products are used “out of spec”.
This is an insanely messy job with extremely toxic and etching chemicals. Chromates (in Alodine) cause cancer and is forbidden everywhere due to environmental laws. It one of the most nastiest stuffs in existence. Poly Urethane contains icocyanides. Icocyanides can make you sick for the rest of your life and cannot be stopped by a coal filter mask. A pressurized breathing system is necessary, and be sure to protect all open skin etc etc. That’s only the start. The aircraft has to look good as well, and for someone that has never painted before, the whole thing is just way too much.
When you start to examine it, you find out this recipe is way out of proportions. For an F-18 that shall hold together for 30-40 years on a carrier – yes. For a homebuilt that will be flown 50-100 h per year, almost exclusively in nice and sunny weather, and hangared the rest of the time it is like shooting small birds with a cannon. A simple and easy to use, non-toxic etch primer and an easier acrylic urethane top coat will make your airplane last much longer than you will live, and it will look just as good. But this brings you back to square one again, you have to chose from any of the 100 answers at random and thousands of products. You still have no idea if you are going to pull it through, if the end result will be OK.
When you have a factory built aircraft that is alodined, epoxy primed and a solid top coat of Poly Urethane, then removing all that, exposing your aircraft to acids and chemicals for no good reason seems like madness to me. You risk destroying your aircraft. I cannot imagine this process can be done without corroding large areas that shall not be corroded. It is not even necessary. You can just buff it down to the epoxy primer and apply new coats of PU. If you by accident buff too deep, then simply apply a thin coat of some fresh Strontium chromate epoxy primer, and it will last forever again.
All aircraft that where blasted looked quite bad. You see all structural parts, as the aircraft skin was strong enough to not be blasted away. Even with low pressure the very thin aircraft skin is very easy to dent in. It looks real bad, especially with new shiny paint. IMHO chemical stripping is the most senseable option for a metal aircraft.
Homebuilders willing to do their own paint job, might want to take a look at Stewart System, they paint and fabric glue using water based instead of solvent based technology. Which might be better if you want to paint your aircraft at the garage at home.
I have looked at Stewart systems. It has had many problems, and is difficult to use. ACS does not even have it anymore, not the top coats. Their technology, and I guess all waterborne products, is based on mechanical adhesion. I guess I will end up flying an unpainted aircraft also
Chromates (in Alodine) cause cancer and is forbidden everywhere due to environmental laws. It one of the most nastiest stuffs in existence.
Nastiness of chromate is a bit overestimated: it’s really bad if you ingest or inhale it, but fairly harmless on skin contact. Essentially, applying a liquid chromate solution is much less dangerous than sanding a chromate primer (with dust being produced). If I remember correctly, chromate-based Alodine is prohibited in the EU but not in the US. There is also a new chromate-free Alodine formula (blue label instead of red). The most convenient form of Alodine for relatively small surface areas is called Touch-N-Prep – it’s a huge felt-tip pen with the stuff. Expensive as hell but worth it.
There are mask filters for isocyanate paints. I have one here – expensive at about GBP 100 for the filters and GBP 150 for the full face mask.
Whether one would use the isocyanate (“2K”) paints on aircraft is another matter. Most likely not. One would use epoxy primer nowadays (zinc chromate etc is WW2 stuff) and for the rest there seem to be various options. Socata use MAPAERO paints which are a bastard to buy (the mfg is incredibly arrogant) and no paint shop I know of uses them.
It is also easy to get a dodgy paint job which peels off. I have had spots on my plane, and I have seen TBMs on which long strips peeled right off, leaving the primer behind. And they certainly do have the facilities… There is so much to get right in this business…
One important factor to take in account that for a certified aircraft you will need an a paint system which is approved by the manufacturer. Where some manufacturers says you can use “any” paint system, some have a limited numbers of systems you can use.
I do know two people who did their whole fabric aircraft using Stewart systems a couple of years ago. They where quite enthausiastic about this system. It doesn’t look bad. However IMHO it wouldn’t be fare to compare an experianced aircraft painter with a first time DIY-er. The regular products smell quite bad, and can imagine the neighbours can not enjoy that smell when building or restoring at home. I can imagine that DIY-er can enjoy building the whole aircraft including fabric covering and spray painting.
All quality top cotes are cured by icocyanates. Either as poly urethane or acrylic urethane. Primers is a whole world on its own. I have tried all kinds of stuff from cheap spray cans to expensive strontium chromate epoxy used by Airbus.
I also use a jointing compound based on barium chromate. Alodine is particularly nasty because you need huge amounts and you cannot simply poure it out in the sink (at least I am too “proper” to do that).
Have to look at that mask. Who is producing it?
I will look when I get home but IIRC it is from the huge 3M range. The mask looks like this.
Don’t get your hopes up… that’s not me – I am not as good looking 
You don’t get the tiniest sniff of the stuff in it. But I would still not do 2K spray work indoors. I pick a calm summer morning and do it in the garden.
Thanks. This beats the hell out of a pressurised breathing system at 1500-2000 all in all that will only be used once. A quick search and most major brands have isocyanate filters.
This only shows the complete nonsense found in both real literature and online and even by talking with people. Isocyanate filters are not mentioned anywhere.
Thanks again. Life became much brighter
Just a note on this icocyanate thing. It turns out there was a hysteria like situation in the 90s which lead to demands for pressurized air (health regulations for workers). This works OK in a controlled environment, a factory for instance, but is a real nuisance in the field. The Swedish army scientist did some experiments, and found that some coal filters has no problem filtering out icocyanates, and a combination of full mask (for eye protection), high quality gas filter (type ABE) and a particle filter (P) would eliminate all dangers. The only problem is the icocyanate filtering is degraded rapidly with moisture in the air, and thus the service time for icocyanate filters are short.
Isocyanate filters from Sundstrøm costs 15-20 €.
