Watching Paint Dry: The unexpectedly interesting story of car coatings
edconway.substack.com
edconway.substack.com
There's a limit on the number of tries you have to "repair" the paint job, because the vehicle has to go through the oven again to bake the coatings. The trips through the oven affect more than just the paint. Some panels are filled with foam; there's internal sealant and glue, and external sealant. All of those things don't really love being baked too long. For the shop I worked in, we got 2 tries to repair.
The main limit on repairs though? The windshield. Windshields are glued in with specialized urethane 'caulking'. They have to stick to the paint, and the paint has to stick to the body. That is only certified reliable with less than 5 trips through the ovens (in my shop).
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Paint is the hardest thing to get right in the whole assembly process, because there are so many process variables. Temperature and humidity (dew point) are the biggest besides the actual paint mix, but there's also unexpected problems from every direction. Our solvent paint process (pre-2013) was very vulnerable to siloxane (silicone) lubricants. Someone in IT applied some lubricant to a label printer and ruined hundreds of paint jobs. Livestrong bracelets also ruined at least a hundred paint jobs. Someone did weekend work on the roof? Congratulations on your dust quality spill (spill means a bunch of problems).
All of the parts of the paint have to work together, and that includes things that you don't think are paint. The body is just dumb metal, right? Of course not. The metal panels have oil on them in stamping, and they MUST stay oiled right up to the point where the body takes it's first bath. If too much of the oil has evaporated, then you start getting corrosion, and in many cases you won't be able to tell until the vehicle gets to the customer.
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Paint shops have the most complicating routing of any part of automotive assembly. The electronic quality and build data has to be synchronized with the physical process, and that data package can be updated by several different systems. Then either IT or OT (operational technology) can make a routing decision, or an individual can use a key switch to manually change routing. "Why did this vehicle go here" is not a straightforward question to answer sometimes.
This gives me a deeper appreciation for cars with plastic body panels. I also wonder if DeLorean Motor Company took any of this into account when they designed the DMC-12 with stainless steel body panels.
And yes, that's a big reason why they went with stainless. Stainless steel does corrode, just much less visibly than regular steel. It also has different physical properties like work hardening etc. It's also VERY expensive. Salty napkin math says $10,000 more for the Cybertruck.
I was thinking about "molded-in color" panels like the old Pontiac Fiero. That makes sense, though, re: painted plastic panels. They'd be a whole different ballgame and there's, I'm sure, interaction between the paint chemistry and the plastic chemistry that's probably pretty hairy.
I bought 2 pairs of the same shorts a couple years ago, one in blue and one in olive. Both were used almost interchangeably in terms of exposure to sun, dirt, washing, and salt water. But on the green ones a section of the waistband is clearly differently colored where on the blue the colors still match.
Droplets were enough to cause problems - there's no hiding problems on a car's paint job and customers are VERY demanding.
I toured an assembly line a few years ago. The guide told us that in the 1970s they had teams of people watching iron/steel prices, when they thought the prices where at the low they made a massive order of all iron that factory would need for the next few years. When the factory when to just-in-time (sometime in the 1980s or 1990s) they couldn't do that anymore - but they also got to get rid of all the equipment to de-rust all that stored iron: since every raw material was shipped out as a final assembly in a week there was no time for significant rust to form and so they avoided a lot of problems.
You can still get squeezed so either way. But that has close to nothing to do with JIT, JIT just concerns the delivery bit (over simplified of course).
I was wondering how realistic that really is to DIY or if I’m kidding myself. Sound like even if I rented a stall in a paint shop for a few weeks, I won’t have the time to finesse the technique to get a good end product, especially with how much more finicky I understand the chameleon paint to be.
I don’t care so much about getting the matching perfect - “it was my first time” is a perfectly cromulent excuse in my social circles - but I do want the paint job to be good enough so that I’m not redoing it every year or two (I hate sanding). What should I exepct?
Only advise I can give is to get some cheap paint and some kind of panels and start practicing.
Another piece of trivia is that Fender, the guitar company, has often used automotive paints for its guitars. The reason is not just availability and durability, but that it accurately tracks recent color trends.
Most Fender guitars sold today are still in those "custom" Duco colors from the late 50s and early 60s. (The standard Stratocaster was a burst color and the standard Telecaster was butterscotch or blonde. Any of the Duco car colors back then was a "custom" option for an additional charge.)
Before the Model T assembly line in 1916, most manufacturers did something like 6 or 7 coats by hand because it was such thin, slow drying varnish. And to get that nice shiny enamel surface we are used to with hand brushes, they had to alternate the direction of the brushstrokes between every coat as well as sand it. In addition to time, this is a huge QC issue.
Part of the magic of the all-black Model T is that you can just dip parts that can be dipped, Japan parts that can be Japanned, and pour paint on parts that cannot. At final assembly they will all be matched up together without any mismatching paint jobs.
And we cannot understate how magical the introduction of asphaltum and naptha were to the paints. This was still pretty new technology then and the precursor to our modern petrochemical derived paints and even plastics. You could get thicker coats that dried faster. So paint could just be poured on and the surface tension would smooth the surface perfectly. And they were more durable because they produced a more flexible coat.
One of the innovations of the Dodge Brothers (that Ford later copied) was that by using more metal body components, not only do you save on labor (working with wood is much more skilled than running a metal press) but that metal can withstand the much faster oven-baked finishes.
The change from VOC-borne to water-based paints was also a big deal for the environment. The lacquers did a good job, but imagine living in a neighborhood where several tons of toluene or acetone was being evaporated into your air every hour. In places like LA, this process was a huge contributor to smog in the 1960s/70s.
We switched to water based paints in 2013 and that really helped with the VOC.
My neighbour was a car painter for decades he died of dementia. My Dad and grandfather had a house painting business in the 1960s/1970s using leaded paint for most of that time. Both Dad and my grandfather died of lung diseases.
A good endorsement of it is that the Chrysler LX cars, which shared more than a few W210/211 bits, have been on sale with only cosmetic updates since 2005...
Also, Tesla isn't all automakers.
Not that Teslas are bad cars, far from it, but tue delta between perception and substance is larger than anything German "Premium" OEMs could have ever dreamed of.
Most 2k water based urethanes with isocyanate hardeners are ~zero VOC (and colorless + odorless at less than harmful concentrations) but much more toxic to those spraying and within inhalation range. Thankfully we are moving to iso free formulations.
It happens that the isocyanate reacts with moisture in air fast enough that it won't harm many others but again, VOC != Toxicity.
I would rather have non toxic air pollution than colorless odorless toxic gas, and there are plenty of examples of VOC regulation generating the second.
It's one of the fun lies that paint companies sell (0 voc = safer for you. Non VOC is good for environment in general but tells you nothing about safety)
Acetone is absolutely a volatile organic compound (VOC). It might not be toxic, but it's an organic solvent with a high vapor pressure at relatively low temperatures.
Since the definition here is the regulatory one, it is not a VOC as we're talking about.
It is the main carrier in almost all solvent borne VOC compliant formulations of coatings
As a result, for example, roughly all solvent borne wood coatings that are VOC compliant use acetone these days. This has fun effects. They used to use, mostly (but it varies a bit), n-butyl acetate.
Of course, acetone flashes off way too quickly, making it almost impossible to get coatings to level and flow properly. So the real result is that the coatings are made higher solids and then get reduced by the user with a significant amount of VOC (toluene, NBA) so they are usable again.
So sold VOC compliant but not really in practice, and everyone looks the other way because they don't really generate enough pollution to be worth cracking down[1].
[1] Moving to water borne is expensive and tricky. For example: They mostly spray conversion varnish which is cheap and easy, and resistant to almost all chemicals. Consumers want cabinets/etc that don't get stained when you get ketchup or wine on them. In water borne, they'd have to spray 2k urethane to get the same resistance, but doing so safely requires supplied air setups that are quite expensive, at least until iso-free formulations get better.
So changeover is quite slow.
Toyota's electrodeposition and prep process can be seen here:
https://www.boredpanda.com/car-paint-deposits-fordite-detroi...
Many dozens or perhaps hundreds of "watching paint dry" cycles results in some spectacular agate-like specimens.
https://www.youtube.com/watch?v=b_hgPinCZks
I was quite surprised at how important paint actually was to car production.
e.g. if you see a Tesla in other than white, red or blue, then it's probably:
https://www.3m.com.au/3M/en_AU/p/c/films-sheeting/vehicle-wr...
> By the early 1920s, two-toned cars were the rage, and that created a major headache for the automotive industry. To craft this duo-tone look, one portion of the car had to be masked off while the other was painted. The problem was nobody knew how to do this well. So automakers and auto body shops improvised. They glued old newspapers to the body and windows with library pastes, homemade glues or surgical adhesive tape. This helped create a sharp demarcation between the two colors, but the adhesives stuck so firmly that trying to remove them often ruined the paint job.
> At the time, 3M primarily manufactured sandpaper and other abrasives. One of Dick Drew's jobs was taking samples of waterproof sandpaper (another 3M invention) to nearby auto body shops for testing. One morning in 1923 he walked into one of these shops and overheard "choicest profanity I'd ever known." Yet another paint job was botched and the worker who'd done it was furious. Drew had seen this occur on many other visits, but this time he spoke up. He could, he said, produce a tape that would end the painter's torment.
I know there are some interesting stories behind titanium dioxide production, the use of which is critical to making paints vibrant and opaque [1].
Further I have a pet theory that the recent trend in 'flat' automotive paints (without the apparent depth and larger suspended metallic flakes common in decades prior) has been enabled by some kind of technical advance as well, not just a change in consumer tastes, although I have no evidence to support the idea [2]
[1] https://www.theverge.com/2014/3/6/5476904/china-stole-the-co... [2] https://www.latimes.com/business/story/2023-03-07/la-fi-car-...
I've wondered about this as well. One theory I've had is that older paints used lead based pigments which gave a glossier finish, but are no longer used. I also do not have any concrete evidence to support this aside from pointing out that automotive paint was exempted from the 1978 (US) lead paint ban.
Then there's composite gliders. Gelcoat is sprayed into molds before layers of fiberglass, Kevlar, or carbon fiber alternated with adhesive is laid into the mold.
Gelcoat durability is problematic. Eventually you have to sand WITHOUT damaging base layers before repainting.
Composite adhesives can be toxic. I know a canoe builder and a glider repair engineer who died prematurely – and two harpsichord builders.
I guess so if you don't count what it takes to make aluminum and steel.
Once production was shut down at my plant because it was too cold and the natural gas company said they had to use the gas for residential customers.
Is that actually the conventional wisdom?
https://www.youtube.com/watch?v=PLOPygVcaVE
1.3M views! I found the plot a little thin (drum roll).
" Cellemail le premier email a froid Francais / Cellemail the best French cold enamel "
So, I think it's french for enamel? Based on that link.
I personally like to express my personality in other ways. The last thing I want is a car screaming some garish hue. Especially since I can do things like match clothes to my mood and the season, but I can't get my car repainted every day or every three months.
Apparently this has to do with how the economy is doing. When times are tough, people like boring car colors. Something about ease of resale and broad palatability in car dealerships.
https://www.cnbc.com/2020/09/22/most-cars-are-painted-one-of...
Was talking to a Mazda salesperson recently and he was complaining that the first five or six of the new CX-90s they were being allocated are all white. Though looking at their website they have some red and dark blue ones on the way now, so maybe that was just the first production run.
If people stopped buying white today, Mazda would stop producing it tomorrow.
I stand by my original point that it's tasteful. Classic shades of white, gray, silver, and black are in good taste, which is why people buy them. The buyers aren't saying "I want a boring color", they're saying "I want a tasteful shade".
At least it's not beige, which would only be boring
Ugh, if the 1990's are calling, tell them I'm not home!
Meanwhile at Mazda, I can see "zircon sand" working for the CX-50, but I'm skeptical on the Miata https://www.caranddriver.com/news/a41995585/2023-mazda-miata...
Unless it's such a weird choice that it somehow transcends boringness?
I have a grey car, but I am fully aware this is the case just because I am a terminally boring middle-class denizen, mass-produced, and absolutely non-remarkable for history.
If you like model xyz, and you like red, but we only have it in Silver, you'll probably buy it.
If you like model xyz, and dislike vibrant colors (very common), you won't buy the red one we have.
And the blue option isn't available, so white is it. If they had literally any non-red color we would've bought it, but they didn't.
Audi will happily get you a Lamborghini yellow q5 if you want.