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Easiest way to prepare milled steel for priming, or painting, or weather proofing with a clear coat

Q. What are some of the simplest, and easiest ways to prepare milled steel in order to prime it, before painting it, or to weatherproof it with a clear coat. I read epoxy was more durable and longer lasting than say polyurethane. I also read on Google that you have to remove some type of coating/finish on the raw steel before priming--the process though necessary, seems arduous and cumbersome.

I am nearly 75 and think I bit off more than I can chew. The project in question is a stand alone mailbox and after seeing pictures of it being painted or powder coated, I thought I could do that myself with a little help. Not knowing that to powder coat it would be cost prohibitive, on top of being guilt ridden for buying such an expensive mailbox in the first place. There are very smart professional people on this site. So much advice on Google can make my head spin. If someone were will to tell me the simplest DIY methods to prepare the steel, prime it properly, and how to paint it with a weather resistant paint, and/or how to seal it afterwards with a weather resistant clear coat, I would be forever grateful and ecstatically happy. Something that what I thought would be a simple matter to paint and weatherize is causing me a lot of additional stress. Thank you!

E Wilkes
- Baton Rouge, Louisiana
December 13, 2022

A. Hello E. It probably doesn't need to be complicated.

But first, when you say "milled", I don't think that's quite the right word. Milled means machined with a milling machine, which hogs a finished shape out of a more solid block of material; for example the wings for super expensive fighter jets are milled out of a single large block pf aluminum. A sculptor uses a chisel rather than a milling machine but also leaves only what s/he wants, chipping away everything else in the large block.

I think you are actually saying that you have "mild steel", which means non-alloyed, non-hardened, everyday plain old steel.

naval jelly

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As the first step you can sand it if that's not too much work; if it is, then skip it. Next you can treat it with naval jelly or rust converter [on eBay or Amazon]
But again, if it's new steel and not rusty you can skip that -- although it's better to either sand it or use rust converter [on eBay or Amazon] , and it's optimal to do both.

Then you simply paint it. Brush or spray, whichever you wish. A primer (any paint made for metal), followed by a finish coat, or two finish coats. The reason for two coats is both to make it a bit nicer looking and also minimize the chance of pinholes or missed spots. You can clear coat it if you wish but I'm not sure there's much real advantage on the first go-round.

Polyurethane based paints are made for outside whereas epoxy doesn't hold up well in sunlight. But don't make it so complicated -- just go to the hardware store and buy Rustoleum or Krylon or similar brand paints made for metal. Usually they'll have a little picture of a wagon, or lawn equipment, or a patio set to convey the idea that they're made for outdoor metal.

To the extent that it's not too much work, avoid getting salt or fertilizer on the mailbox. In 2 or 3 years if you're still around (I'm 76 myself), wash it down, then brush on a simple clearcoat like Everbrite [a supporting advertiser] to freshen the look and extend the corrosion resistance. Luck & Regards,
pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha - Pine Beach, New Jersey

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