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Looked for a better stack exchange forum to post this on but did not find one. Looking at buying a used shipping container. The guy who is delivering will paint it but he uses latex. I'm wondering what type of paint is best on a shipping container, and if you can paint that directly over the shipping container, or if you need to prime the entire thing first.

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    You're essentially asking about how to repaint a metal surface that has some existing paint on it, right? Is the container rusty? – JPhi1618 Aug 23 at 20:46
  • Obviously you want anti-fouling paint! – Hot Licks Aug 25 at 0:06
  • @HotLicks that's brilliant! Now I must design a canal boat to resemble a half-sunken container. It would be very, very easy to portage, as it could be effortlessly handled by trucks, trains, or even a container ship! At the international port you just have the boom picker guy drop it directly in the water. Thanks! – Harper Aug 25 at 21:41
  • Thanks for all the info everyone, I ended up paying the extra for s new one, after all the pain, labor etc, the price difference was not that’s significant – user379468 Sep 12 at 15:39
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Nononono! Tell him to save his latex paint!

I sometimes paint things at industrial sites. Latex works fine on the buildings, but when it is used on steelwork of any kind, it turns into an unmitigated disaster, that you pay for for decades.

This is a metal thing left outdoors. It will have much higher extremes of temperature than a house's walls. It will also have thermal expansion unlike a house. There is also an adhesion issue with the { oil-base, possibly LPU } paint that was applied in the factory (in east Asia where nobody cares about enviro regs).

Latex has managed to win on architecture because it's been engineered for 50 years to be a good fit. Other than that, the only reason anyone even has a conversation about waterborne paints is to "spare the air". But it doesn't spare the air to paint a bodge job that fails, is reapplied shortcut style, fails again and ultimately must use harsh chemicals to totally remove for a proper coat. That's like those early "low flow" toilets you had to flush 5 times.

The greenest thing you can do is lay down paint that will last. Here's how:

  • Given this thing's long saltwater career, I would hose it down good and plenty while giving it a good old "carwash" style wash. Salt also contaminates paint.

  • Remove any identifiable rust either with a wire wheel or sandblast down to SSPC-SP10 near-white metal. Get primer on it ASAP. See below.

  • "Scuff sand" every surface you want the paint to not fail. (I.e. Every surface). Scuff sanding means knocking the gloss of the previous layer, to create microscopic "jagged mountains" for the new primer/paint to lock in to. Anywhere you blow through to bare metal, prime soon.

  • wash off all contaminants, by optional carwash style washing, then solvent wipedown - the latter preferably the 2-cloth method. Straight paint thinner is the classic, but they make low-VOC versions for Spare the Air territories that are terrible paint reducer but a fine wipedown solvent. You don't want soap residue or mineral residue from your city water (yes, it has minerals; if it didn't, it would leach them from pipes).

  • Prime anywhere bare metal is exposed, e.g. Where you removed rust or scuff-sand blew through on any corners etc. Sandblast or blow-through is excellent "prep" and you can use all sorts of primers. Wire-wheel is less effective prep, and there, use an excellent over-rust primer such as ordinary Rustoleum 7769.

Don't turn your back on bare metal. It will rust in a couple of hours and compromise your primer's performance.

  • If your topcoat requires a compatible primer, or if you're worried about topcoat compatibility, then you prime the entire container. For instance, I like LPU topcoats, but they require a barrier coat of epoxy primer underneath.

  • Finally, your topcoat: Normally I roll-and-tip because I hate the PPE (masks, hoods) and extreme masking required for spray. However containers are very irregular and don't need much masking, so it might be worth setting up for spray.

For me, if this were a quickie, I'd have a conversation with a Sherwin Williams Industrial dealer about their best 1-part alkyd (oil) urethane. If I were serious, it'd be LPU all the way. My question is, "Do I ever want to paint this thing again?"

I mention LPU, this is a 2-part (A and B part, like an epoxy) which combines a urethane A-part with an isocyanate B-part. (If this sounds scary: exactly.) The isocyanate and urethane splice to each other forming a poly-urethane molecule that is extremely long - far longer than can be obtained from a 1-part polyurethane paint, where the molecules are short. This creates an extremely tough finish. Any 2-part paint such as an automotive paint will be something like this, it's also used for aviation and marine.

LPU and other 2-parts are safe as houses once it cures, and the isocyanate (or BPA) in the B-part will stay in the resin and not evaporate by itself, so it's safe to brush (don't get it on your skin). Spraying it is a whole 'nother kettle of fish. You're turning it into a fine mist, and you must not breathe that! At all! The factory recommends an external air supply. I prefer marine paint since it is less encumbered by environmental regs, cheaper and made to brush. It's perfectly appropriate; it's a marine container after all.

This safety issue is why 2-part paints aren't marketed to consumers, except for garage floor paint which is always rollered.

  • Can't edit this at the moment, but it would be helpful to identify "LPU" as "linear polyurethane". – Daniel Griscom Aug 25 at 11:03
  • @DanielGriscom I'm afraid to do that, because then people will hear "Blah Blah Polyurethane", and go "Oh, polyurethane! I saw that at the hardware store, I'll just get that!" – Harper Aug 25 at 17:12
  • Perhaps boneheads will misread your explanation, but if you don't explain then nobody will know what you're talking about. – Daniel Griscom Aug 25 at 21:24
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Depending on your desired finish, I suggest using automotive paint. You'll definitely be doing some "scuffing" to get the paint to stick, and priming as well. You might also consider a roll-on truck bedliner for a more rugged look, but I hear it is prone to UV fade.

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    Automotive paint has a couple of problems. First it is chemically similar to LPU, and requires extreme protective gear. (Many people don't, and damage their immune systems as a result). Second, the clean air authorities attack the low hanging fruit, and autopaint is a huge market used right next to houses in cities, so it's been thrashed by waterborne/low VOC requirements. I favor your sentiment, however, and the place to get uncorrupted paint of that technology is the Marine market. It is largely untouched by regulation because it's small. And the paint is cheap! – Harper Aug 23 at 21:40
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This site recommends alkyd enamel paint, and this paint specifically for skips and containers is described as

modified alkyd resin, pigmented and dissolved in white spirit, as a solvent. A specifically suitable hard wearing enamel gloss for Skips. A highly durable oxide gloss with a rust inhibiting formula preventing the risk of corrosion.

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