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Einhorn 06-12-2011 05:21 PM

Paint for Rust-Prone Exterior Metal Railings (Oil-Based Metal vs Epoxy vs Urethane)
 
A few years ago we contracted the re-painting of exterior metal railings to a painter who specified that they would remove loose rust, and then prime and paint with rust-paint. The rust later returned within a year.

This year, I’ve discussed the subject with many others, who convinced me that the way to go is the use of a “rust converter”. The brand ‘Qurox’ was recommended although the idea as I understand it is relatively standard…an organic acid (usually tannic acid) mixed with a co-polymer, and the combination reverses the oxidization and seals the metal, acting as a primer.

The manufacturer of Qurox recommends scraping/grinding loose ruse off, then applying 3 thin coats of Qurox, with an hour to dry between each coat. Although they are not in the paint business, he recommended that we complete the job with 1 coat of Epoxy paint.

Our painting contractor (different person from prior years) agrees with all of this, expect for the Exoxy paint. He commented that Epoxy paint is excellent, but is also very expensive and he didn’t see the benefit from the added expense, especially in light of 3 coats of Rust converter.

We’re in Canada, where Oil-based paints will be largely removed from the market by next Year. Our painting contractor recommends using as much Oil based paint while we still can.

He didn’t mention this, but one possible consideration is that the original paint (7 years ago) is oil-based paint. Since we won’t be stripping, and the only primer will be the rust-converter, is it fair to say that Oil-based would work better? And if we were to move to epoxy paint, we would either need to strip the existing oil-based paint, or prime it with something in addition to the rust converter?

A final consideration, I read that Epoxy paints, while strong, don’t hold up well to Ultra-Violet radiation. These metal railings get a lot of sun.

The last recommendation I received was to use a "Urethane system" such as Pitthane, but warned that it would cost quite a bit.

I didn't get a clear understanding of what's the issue with standard oil-based metal paint, if oil-based paint is still available? I've seen that it holds up well over many years if the metal is properly prepared.

Thanks for any suggestions.

user1007 06-12-2011 06:42 PM

Epoxy and urethane might have been good choices when the metal was new and free of corrosion. It will still work if you get all the oxidation off. Electro finishing is another possibility but you would have to drag them somewhere.

Rust conversion paint is expensive but a good option. You might check to see what marine finish products are available in such formulations. It is cursed by Navy squids the world over I suspect.

If the corrosion is not so extensive you can grind or sand it off? A rust primer and oil based finish will work fine.

As for using oil based paints because they may soon be banned? If people had been more careful with the solvents and disposing of things, they probably would not be banned even though they do have higher VOC. You should still be able to get special purposed finishes.

Einhorn 06-12-2011 09:58 PM

What would be a good paint to use on top of a rust converter/primer that specifies, "for maximum protection, a solvent based top coat must be used. Do not use water based paint to top coat". ?

HDPaintPro 06-13-2011 09:08 AM

The industrial enamel product from RUST-OLEUM is one of the best products for rust vulnerable metal. I have used it on many occasions for wrought iron rails and have been able to revisit them several years later to find them still protecting.

http://painting123.com/images/produc...ssBlack_GL.jpg

DannyT 06-13-2011 11:27 AM

i would prime with rustoleum primer for rusty metal. we used to use it on rusty beams in basements and it worked great. then paint with the suggested rustoleum paint.

Gymschu 06-13-2011 05:03 PM

I give another "thumbs up" to RustOleum.........painted a fire escape 8 years ago.......rusting pretty badly.......applied rusty metal primer and two coats of gloss black.....it's still looking as good as the day it was painted.

Einhorn 06-19-2011 10:39 AM

Painter started yesterday, on one balcony which I supervised. Affter grinding off any loose rust and paint, he put the rust converter in his spray gun and began spraying.

The amount of rust converter that was required to coat everywhere was surprisingly high. Since we're talking about railings, its not surprising that a lot more is required when spraying than when using a brush. But at this rate, we would use $4000 of rust converter.

He says that he prefers spraying because it gives an even coat everywhere. So he will simply turn down the rate at which it sprays the converter in order to cover everywhere with what we have.

Only about 10% of the railing is rusty, and that's been ground down. The rest is the original paint, which has been left on since there's no sign of rust. Spraying that 90% with rust converter does give everywhere a smooth coat. It does etch the old paint which the documentation says will serve to prime the old paint.

But I'm thinking that a better strategy would be to only put rust converter on areas where there's rust, and/or rust that's been ground to metal. We would get more rust converter on these spots, the spots that turn black, but at the expense of using it as an expensive 'etch/primer' for the old paint. The old paint could be painted over in a standard way (either just straight paint, or if needed a standard primer then enamel paint).

Which of the two options above would you recommend...thin layer of rust converter everywhere, or save it and focus it on the rusted areas?

user1007 06-19-2011 10:48 AM

The last such fence I worked on was an antique wrought iron thing about waist high friends had wrapping around the front of their Queen Anne Victorian B & B. I did it with a brush because I did not dare spray. That fence was like a sponge so what you are observing is not unusual. Spraying in this instance will actually save some paint but make sure you put enough on for the chemical reaction to do its thing.

Einhorn 06-19-2011 12:10 PM

Thanks for that encouragement. The point I was making is that 90% of the metal is intact and rust free. Spraying everywhere will necessitate a really thin layer everywhere.

I feel we'll be much better off just using the converter on spots where rust has been found, and in those locations using it abundantly.

Using the converter to prime the other 90% of solid metal means we're using a $200/ounce primer. We could even just use a standard primer, or paint directly over the existing enamel by simply cleaning it first.

housepaintingny 06-19-2011 08:41 PM

Scrape and grind any loose, flaking paint and rust off. Apply Sherwin Williams Kem Bond HS oil base primer to any bare and rusted spots. Top coat with acrylic DTM semi-gloss from Sherwin Williams.


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