Clear coating to seal a rust patina finish on metal

A. Hi Tommy. We'll see if the e-mail addresses of those who commented on Penetrol still work and if they respond. There are many brand of clear coats, and we don't really like to focus on brand names ( huh? why?). Some are available in satin/matte finishes, which will help limit the shine, but all coatings will make the metal somewhat more shiny and darker for the simple reason that rust is always a rough, etched, powdery finish which scatters light, and whatever coating you use will be smoother, not scatter the reflection as much, making the reflected color shinier and more saturated.

Please consider Everbrite [a finishing.com supporting advertiser], which is available in matte. They have a great web page detailing the issue of protecting rusted finishes ⇨
... plus they help make this page possible for you :-)
Luck & Regards,


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

A. Hi A Powell,
I tried to answer that one just above. Please visit the suggested site which goes into a lot of detail on the issue.
Luck & Regards,


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

A. Hi. If you mean a one-part polyurethane such as is frequently used on wood, my experience is that most have no substantial UV resistance for outdoors, so I'd look for one specifically labeled as UV resistant.

If you are talking about a two-part formulation such as an automotive clearcoat, it should be fine for a while, but don't expect miracles -- the coating will have a hard time getting full adhesion on a powdery surface (if the coating holds onto the rust but the rust doesn't hold on to the steel, it can flake off). If natural rusted appearance is not the primary concern, you can apply a rust converter ⇦this on eBay or Amazon [affil links] before the polyurethane

Luck & Regards,


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

A. Dear Mark,

A good polyurethane should do the trick. I would usually recommend an acrylic base coat followed by a urethane. This makes the urethane much easier to strip, when it comes time to repair/maintain the patina and substrate.

adv.
Contact me if you would like more information.

Regards,

A. I think that you can use proprietary polyurethane paint or spray. Some of them contains rust inhibitors (Krylon spray). Good luck!

A. I have been using the same approach to accelerate rust and have been experiencing the rust peel you describe. It is my belief that the acid causes the rust to happen too fast. I suggest you experiment a little with vinegar ⇦in bulk on eBay or Amazon [affil links] . That seems to work fairly well and quickly. Also be aware that the texture is different than with the acid.

A. In Response to neutralizing.... baking soda [in bulk on eBay or Amazon [affil links] will neutralize acid. Wipe the surface with water/baking soda mix and drying it fully, quickly. it will stop the patina process.

A. Hi, Richard. I suspect the reason you couldn't find a great answer is that there may not be one :-(
It's said that a chain is only as strong as its weakest link. Here we have a link of steel (your welding bench); then a link of loose, powdery, non-adherent rust. Then a link of clear coat. And people report that as stress is put on the clear coat, the clear coat pulls off, "taking rust with it".

But I suspect that if the rust is quite thin, such that the clearcoat can "wet" it all the way through to where the clear coat can actually grab some sound steel, you may get acceptable adhesion. Good luck.

A. Automotive clearcoat. Seals the rust without inhibiting the appearance, and the thicker you lay it on, the more protected you are. If it gets severely scratched, just buff with a little clear coat polish and a buffing cloth.

A. Hi, Rose. A couple of thin coats is probably best, but you must brush any loose rust off first. A chain is as strong as its weakest link. If the rust doesn't adhere to the substrate, it does no good to have the clearcoat adhere to the rust -- it just comes off as a package deal. Clearcoat is not shrink wrap; it has to adhere to the base steel or to rust that itself has some adhesion :-)

Regards,  

A. For my restaurant in Portland, we formed sheet steel panels to fit our back bar, laid them in the parking lot and sprayed them with muriatic acid ⇦this on eBay or Amazon [affil links] (diluted a lot) and salt water and let the rain finish the job. When finished it looked like marble and burled wood--nobody guessed it was rusted steel.

We burnished it with fine steel wool ⇦this on eBay or Amazon [affil links] to remove any powdered rust, leaving a smooth and intact finish and polyurethaned everything. We put a few coats on, as I recall.

It was inside and not exposed, but in the 8 years I had the restaurant (before I sold it) it showed no signs of additional corrosion or breakdown of the poly finish.

Looking at clear powder coated finish for my next project.

Michael

A. Hi Marion. Let me first clarify what automotive clearcoat is, in case any readers are confused. It's a "2-component" or "two-part" or "2K" coating material. It is usually polyurethane but it hardens the way epoxy hardens -- in other words it doesn't "dry", it "cures" as the two components react with each other. You have to mix the two components in the right ratio, and must complete the project before it hardens.

There is no reason you can't brush it if you can work quick enough, or do it in several batches. Use cheap disposable brushes as there is no way to clean them. We don't like to recommend one brand over another, but I'm sure a local automotive store will have it. Single component clearcoats can have many uses -- just don't talk yourself into thinking single component clearcoats are the same thing as "automotive clearcoat". Good luck.

Regards,

A. Glass cut to match the shape of table would work if it fits the aesthetic. Or 2K automotive clear coat, as has been stated multiple times.

A. Hi Evenilde. Some colors are pigments, and a clearcoat won't effect them; but some "colors" (like the rainbow sheen of a drop of oil on a puddle, or reflection from a CD/DVD, or the colors of titanium jewelry, or the changing colors of some oncoming headlights) are just diffraction effects. These effects happen because the oil, or plastic, or metal coating is transparent and so thin (partial wavelength) that light waves bouncing off the inside of the clearcoat and the outside "interfere" and cancel out some of the colors of white light, while amplifying the remaining.

The bad news is that any clearcoating will always destroy these diffraction colors because the clearcoating is too thick for partial wavelength effects. I can't say for sure, but I believe this is what is happening to your "yellows" and "oranges", leaving only a brown rust color. Sorry it's not good news, but at least if you know what you're fighting you may be able to figure out what you want to do.

Regards,

A. A great clearcoat I have found for sealing this rusted effect is Motostorm's Glamour clear. Its a polyurethane so more flexible than urethane clears, which has been a life saver on some of the thinner metal projects I've done. It adheres amazingly well to rust. Of course, as pointed out, the large rust flakes can be a problem. Your best bet if you want to preserve the large rust flakes, is to either, scrape them off, put a light coat of clear on, then sprinkle them back on..., or hammer the part with LOTS of clear over the course of a few days. This will form a 'bridge' of strength over the looser flakes.
The small powdery rust can be a problem. But if you can lay your project flat, using the Glamour clear or a good quality automotive clear, add some retarder to it and hammer on one or two hard coats to the project and leave it be for 24 hrs. This will saturate the rust and the slow retarder is just added insurance for more saturation. A good quality clear must be used though. So many out there are loaded with cheap flash solvents.

Yes, you can apply automotive clear with a brush. Mix small amounts at a time. Brush on one light coat, clean your brush while you wait 30 min for first coat to tack up, then repeat until you have the build you want.
You CANNOT use those foam brushes. Automotive clear will melt them. A natural hair brush should work. I'm not sure about others. Also, don't put the brush all the way into your mixed clearcoat. The clear solvents may eat any glue that is holding your bristles in. Then you will have hairs in your project. :(

Try to avoid using Baking Soda. If you MUST use baking soda to neutralize your project, neutralize the project with vinegar after the baking soda. Baking soda will keep your clear coat (or even primer) from adhering to the project at all. Later down the road, especially when exposed to the elements, your clear coat can start to turn cloudy. This is air pockets forming behind the clear as it is trying to delaminate.

What I have done for my rusted effects is hang part vertically, spray with muriatic acid. Wire brush in downward strokes. Blow dry with 100 psi air. Spray part with plain water (deionized water if your water is not neutral). Blow dry again with lots of air pressure. Then I spray it with a good quality solvent based wax and grease remover. Then blow dry again. At this point I like to let it sit in the hot sun for about 30 min while I mix up my clear. I then bring it in, let it get down close to room temp, and hammer with Glamour Clear with a few drops of retarder added. I let sit over night. Then I sand it with 320p Grit paper, and then apply a few more coats of clear until I get the smooth finish I want.

Ed. note: Please see thread 17478 for a beautiful rust-finished table & an incredible pencil sketch on rusted steel, and thread 16945 for a hot woman made of cold steel.

KBS Diamond Clear

on eBay or

Amazon

(affil links)

A. KBS RustSeal clear, neutralizes as well .

A. Hi, Charlene

It's risky to guess what a 3rd party meant without hearing their actual words, but I'll guess...
Some clear coats are single component; but some, like epoxies and automotive clear coats, are two component. You can't use just one part of the two part system: epoxy for example will never dry, but will just remain a sticky syrup unless mixed with the required catalyst or "hardener". I guessing that you went to buy a clear coat system and tried to buy just one component of the two-component system. Good luck.

Regards,

A. Hello again Charlene

Okay, I'm finally catching on to your question. The "automotive clear coats" that people are talking about are not coatings like Sharkhide where a solvent evaporates and allows them to dry. Rather they are two-component coatings like epoxy where mixing the two components causes a chemical reaction that makes the mixture chemically react & harden, as opposed to drying. You can't put the two components in one single can because it would quickly be just a solid hard mass rather than a liquid. The way it is usually done is an automotive painter takes a can of component A and a can of component B, mixes them together, then rather quickly pours the mixture into his spray equipment such that they are sprayed on within a very limited time after mixing them.

Adding to the confusion, people sometimes call component A "clear coat" and component B "hardener", although component A by itself is not really a useable clear coat, just a sticky syrup. So buy the can labelled "clear coat" (component A) as you were doing, but also buy the hardener (component B) from the same manufacturer.

If you don't have professional spraying equipment, you can't spray two-component automotive clear coat*.

However, you may be able to successfully brush it on after mixing the two components. Although I have no experience in that, Adam B. describes it above. This may be what your friend is doing. Use a very cheap brush and a cheap plastic mixing cup because once the mixture starts hardening, they become garbage -- there is no cleaning or washing them. Practice on a piece of scrapped art; don't go directly from no experience to an important piece.

Regards,

2K Clearcoat

on eBay or

Amazon

(affil links)

A. I've been force rusting steel projects for many years and have found a successful process. I wash the steel object with water and dish soap and then spray it with a vinegar and salt solution. This step accelerates the oxidation process.

Once the piece has rusted to the correct patina I wash it in a warm water and baking soda [in bulk on eBay or Amazon [affil links] solution. This step stops the accelerated oxidation. Note, it only stops the accelerated oxidation.

Next I burnish the piece by rubbing it with an old leather welding glove that smooths the rusted surface and adds yet another interest dimension to the patina.

Lastly I coat the piece with clear coat. My best results have come from a matte finish polyurethane, but have also used an automotive clear coating system as well. I usually use several thin coats. This final step seals the surface and essentially stops the oxidation process. The oxygen can no longer cause any problems.

I haven't had problems with my pieces chipping clear coat or peeling rust. I think the key is a light coating of rust, neutralizing the forced oxidation, and completely sealing the surface.

A. Hi, Peter. If you have the ability to mix and spray, I think a 2-component automotive clearcoat might be best. They are relatively thin and durable, and they are probably pretty readily available around the world. But it sounds like Tom D of Minnesota has good advice born of actual experience.

Regards,