Clear finish for untreated mild steel door?

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A. Hi, Allison: your inside door is more practical to clearcoat than Jerry's entry door :-)

Consider the way automobiles are painted and why. First, every edge is turned or sanded so there are no places moisture can accumulate. Home doors are not built that way, and there will be wet areas around the hinges on exterior doors. Second, a good part of the metal on a car is pregalvanized (coated with zinc for sacrificial protection); if your door was pregalvanized, that coating is not transparent and will be gone by the time you sand the door. Automobiles are phosphatized, which is a coating that not only helps paint adhere, but evens out galvanic "hotspots" (areas that due to machining operations and stresses are more active and rust-prone). This is not a transparent coating, so you can't have this on your door either. Then automobiles are electrocoated with a primer; it's not transparent so it can't be on your clear finished door. Then cars are painted, then they are clear coated.

So, when you want a clear coat finish on a door you leave out galvanizing, and phosphatizing, and electropriming, and painting and rely on just a clear coat to keep the steel from rusting. A 2-part automotive clearcoat is the most reliable, but don't be surprised if it doesn't work reliably and to your satisfaction (exterior exposure in a humid area is much more problematic than interior exposure in a dry or air-conditioned area).

No, you do not need to buff it first unless you prefer the buffed appearance. Best of luck!

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A. I found your letter because I have the same problem. I, too, am seeking a solution to the problem. I have some observations you might find helpful. For interior work wax is the best bet. Any rust that pops up can be 00 steel wool ⇦this on eBay or Amazon [affil links] or Scotchbrighted (is that a word?) off then waxed again for a seamless finish. This also works on protected exterior work. The problem with hard finishes is the UV resistance. They break down. The biggest problem is that if you ever get water behind the lacquer it will turn milky or rusty. Then the only way to fix it is to remove all the finish. If you wax, you will never get paint to stick later.... Something to think about.

A. I am amazed at the way almost any question posted on the internet can illicit intelligent-sounding "can't be done and here's why" responses. That drives me nuts.

Clear acrylic spay from a can works very well in this situation.
Basically, it is what's used on automobiles. Comes in gloss to dull finishes. Apply several coats. Note that painting a door may require several cans.

Thanks, "Dirk". I didn't say it can't be done ... of course you can aim that spray can at anything. It's quick and easy, things usually don't have to last forever, and life is short -- so your side of this discussion is appreciated!

I have yard art and I spray that stuff onto it every year or two. It's a practical way to prolong its life when you don't mind frequent re-dos, don't need things rust-free, and aren't worried about the runny look of partially-peeled coats over a few years.

Still, I explained why car manufacturers spend the money to do the many steps that I described instead of doing it your way. It's why unpainted bar-b-q grills are stainless rather not clearcoated plain steel, and why appliance manufacturers use expensive stainless steel rather than clear coated plain steel even for indoor use. I've supervised corrosion tests for many different finishes and can tell you that people who try to keep bright bare steel from rusting outdoors by simply spraying on a clearcoat, or any number of layers of it, will discover its limitations really quickly :-)

My opinion is only my opinion, but at least it's from a real person with some metal finishing experience, whereas yours is posted with a fictitious name :-)

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
January 25, 2010

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A. Hi, Brian. If your home is air-conditioned, or at least not muggy, not much corrosion protection is needed. The wax should be dry to the touch (it's what museums use for their metal objects).
But wax is much thinner than a clear coat, and is something you need to repeat with some frequency, especially if you don't have museum-style environmental control. Since that's probably not convenient for a ceiling fan, I think the clear coat may be more practical, but either will work. Good luck.

Regards,

A. I'd like to second Mooney's original answer, the reason it was 'intelligent sounding' is because it is. He did not say it could not be done.

I'm a professional furniture designer / maker with tons of experience in interior architecture and specifically finishing. It's what makes my work shine.

I have acrylic coated, wax coated, poly coated, you name it, and many times for clients who want 'that steel look'... and for those of you who eschewed chemistry early in life it is a fact of life that no polymeric (paint) coating is / or stays waterproof its whole life. Nearly all coatings, (wax isn't even a 'coating' in this sense) allow molecular water through it's pores. Oil based coatings less so, epoxy based coatings even less so.

The reality is, it WILL rust under any coating, dependent on the ambient moisture, hence galvanization. What you have to do, but only if you want to DELAY this, is remove all rust physically, a wire brush is only enough for very superficial orange rust. Rust makes layers, you need to get UNDER and remove all layers, a scraper is cheap to open the rust pockets along with a twisted wire cup brush on a grinder (brass won't cut it on bad rust, too soft) .

Then, you must deactivate the residual rust chemically with Naval Jelly.
or a similar product that converts that "Rust that never sleeps" into a non active form.

If there isn't ANY rust (and I mean NONE), which is highly improbable, then just paint the damn thing.

Then, put whatever product you want on it. Epoxy will shine, but last a Really long time against rust, a NON-thinned polyurethane or a NON-thinned Acrylic are pretty good too. Wax is just eye-candy, it is very porous to water vapor.

Get all the rust off, be o.k. with light rust re-forming, enjoy your awesome door, and don't worry about anything. Its just a door, and you are a rebel against paint, remember?

A. Hi, Mark. I haven't tried it, but I do see a technical paper on water-thinned shellac as a primer for iron and steel, so I suspect that it will be fine for indoor use. Good luck.

Regards,

A. Hi, George.

If you want the bright metal look for aesthetic reasons, that's fine. But if you think it will reflect heat instead of absorbing it, please touch the shiny metal bumper of a truck on a hot sunny day before proceeding with the project. Solar collectors are chrome plated to increase their capture of the sun's heat :-)

Bright white paint is more heat reflective than shiny metal. This is probably confusing, but the difference between a mirror and a bright white wall is diffusivity not reflectivity. It's not that the white wall reflects less light than a mirror, but that it scatters the light in every direction instead of maintaining a focused image. Good luck.

Regards,

Q. I'm sure what you're saying makes perfect sense, Ted, but I went Googling further and found this -

"What is an everyday example of a good reflector of heat?

A light colored or highly polished metallic surface will reflect a lot of heat (which is primarily infrared radiation). Some people in sunny places put a folding windshield screen up inside their car. The best ones have what looks like shiny aluminum foil on them to reflect the heat."

Read more, wiki.answers.com: What is an everyday example of a good reflector of heat"

If white paint is as just good as bare metal for reflecting heat, I shall use the white paint as it's a lot simpler and cheaper than clear coating the containers.

Many thanks,

George

A. Hi, George. Please see:

en.wikipedia.org/wiki/Cool roof

and azcoolroof.com/downloads/Resources/Article%20Laboratory%20Testing%20of%20the%20Reflectance%20Roofing%20Materi.pdf , "Laboratory Testing of the Reflectance Properties of Roofing Materials" -- especially page 7.

White paint is a lot better than "just as good". It absorbs as little or less heat from the sun in the daytime, but it emits much more at night.

Regards,

----
Ed. note Feb. 2022: That domain no longer exists, and that paper now seems to only be available behind pay walls.

Excellent, Ted! Big thank you. I'm completely convinced. What I thought was a simple matter has turned into a most interesting discussion on cool roofs among my friends here.

Thanks and blessings,

George

! My pleasure, George -- I learned as much as you from the googling. Come February, when it's below zero here, I'll be thinking of you and your friends trying to escape the heat :-)

Regards,

A. Hi Dan. I don't know if buffed wax will rub off at all onto the carpet, but if you don't buff it to death to make sure you haven't missed a nook or cranny, it does sound possible ... so clearcoating is probably better for you.

Regards,

A. Hi Chad. Paints and clear coats are much more rust resistant than bare metal, so if they are involved in either of the finishes, it will probably be okay.

Regards,