Xjyuk

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.

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 identifyable 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 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).




• If you removed any rust with wire wheel or sandblast, or if your scuff-sand blew through any corners or edges exposing bare metal, immediately hit it with primer. If you blew through or did sandblast prep, you have a lot of choices. With good but imperfect prep such as wire wheeling, I've had great luck with ordinary Rustoleum 7769. For lesser prep you can try Rustoleum but expect failure.

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 primer 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, but containers are intricate enough that it might be worth the ridiculous PPE (masks, hoods etc.) required for many paints to set up for spraying.

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

LPU is safe as houses once it cures, but before that, the B-part of the resin is very toxic. (Not the evaporating solvent, the resin that will become solid). Brush/roller is fine, don't get it on your skin. But spraying it, you're atomizing the resin particles, and if you breathe those in...!! (So the factory recommends a supplied-air system). Automotive paint has the same characteristic. 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.

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.