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Old 06-27-2013, 01:14 PM
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Great question, why would it rust?Oxidation. Most coating systems are not airtight.the latest marketing schemes in the industry is now the hype up airtight. This is the problem they have with the bridges they paint them in a couple years later the rust would come bleeding through.the most effective way to deprive the metal from oxygen is by the use of metallic pigments. Aluminium, stainless steel,mataciois iron oxide.the pigment in multiple layers creates a barrier that the oxygen is blocked.The resin is completely waterproof so you have a moisture proof/airtight seal over the metal.the Bay Bridge is a classic example they always continue to paint. The Pittsburgh Homestead high-level bridge went 14 years with less than 5% corrosion. I hope you can understand the misinformation that a lot of people buy into.

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Old 06-27-2013, 02:16 PM
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Interesting, hmmmmm

Brian
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Old 06-27-2013, 05:21 PM
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Ok.. So what's this misinformation you feel people are buying into ??
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Old 06-27-2013, 07:09 PM
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The misinformation is that their led to believe that they paint this black urethane over the rust and its sealed forever.That is nonporous.Not exactly true. For many years they were never told how many coats to apply.The name of this coating system is The three coat polyurethane system. It was named that for reason It works better over rust, because the only thing it'll stick to is rust.it's difficult to paint over so it's not really a primer. It doesn't take sunlight so not really a top coat. It's great for a application under a car when used with the correct primer. Brushes out beautifully got an extremely high-gloss and is pretty chip resistant.
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Old 06-27-2013, 08:58 PM
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Quote:
Originally Posted by Pats55 View Post
The floor pans were new replacement pans installed in 2006 they were E coated from the factory and then the black MCU painted over it. Back to the original question should you leave that e coat on them, or should you strip them, acid wash and then prime them?In my opinion don't take chances that there may be rust under that Ecoat especially with body panels.
I believe the e-coat sticks better and more thoroughly than anything one could spray on because of the electrostatic affinity the paint molecules have for the metal. With that being said, I don't strip the Ecoat, some people do. I've found it's pretty obvious to tell if the Ecoat was applied over rust because it will have a bumpy rough texture in the afflicted area. I sand these areas down to metal before priming. I haven't seen this very often on the panels I've used.
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Old 06-27-2013, 09:05 PM
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Originally Posted by Pats55 View Post
The misinformation is that their led to believe that they paint this black urethane over the rust and its sealed forever.That is nonporous.Not exactly true. For many years they were never told how many coats to apply.The name of this coating system is The three coat polyurethane system. It was named that for reason It works better over rust, because the only thing it'll stick to is rust.it's difficult to paint over so it's not really a primer. It doesn't take sunlight so not really a top coat. It's great for a application under a car when used with the correct primer. Brushes out beautifully got an extremely high-gloss and is pretty chip resistant.
You won't have a difficult time convincing people here that POR, and it's various analogues, sucks. You're just preaching to the choir now, brother.
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Old 06-28-2013, 09:23 AM
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Okay, the sermon is over, since there's only three of us in the church.
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Old 07-02-2013, 11:44 PM
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Three speaking, but trust me the pews are full. I couldn't believe anyone would buy into the whole "painting over rust" thing in the first place, it's just kicking the can down the road.....and just plain lazy.
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Old 07-03-2013, 02:57 AM
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Stroker I agree you should never paint over rust. You would not believe how many cans of this stuff are sold every day. I stood in a booth for over 20 years and dealt with people who believe this with their heart and soul that when it rerusted it was because THEY did something wrong. Due to DEP sandblasting was prohibited on projects for lead paint that would fall into the waterways or surrounding areas.That's when they developed the silver primer to seal it up It was noted that *sandblasting was a preferred prep but where sandblasting was prohibited'' excellent results were achieved with the use of wire wheels and grinders'.' From there it went to the antique car hobby and was sold intact for a period of time.Then everything changed the resin changed,the thinner was changed and the pigment was changed.The people that had it changed had never touched a car or a can of paint in their lives.to them it was the same stuff. And at least three more companies copied what they did.What and how is sold in the industry and what is sold in the car hobby is different, if this technology is used correctly you will get outstanding results.
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Old 07-04-2013, 01:02 PM
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Rust is the result of an electrolytic reaction. That means there are two different metals, and water, and of course, oxygen from the air.

But you say, there is only one piece of steel here. This is the problem. Steel is iron, and carbon, alloyed together. The rust (oxidation) actually starts on a molecular level, between an iron atom, and a carbon atom. there is enough of a difference in the metals that one atom starts the rust on the next atom, with the carbon atom. Just like sticking a piece of zinc, and another metal into a lemon, and making a battery. An electric current will flow, because of the electrolytic reaction.

Different types of metal have different voltages, if used in the same acid type solution. Once steel starts to rust, the rust is also electrolytically active, and even more so that non rusted steel. There is a higher electrolytic voltage between rusty steel, and plain steel, than there is between the iron molecule and the carbon molecule, used to make steel from iron. So, once rust starts, the rusting is accelerated by the presence of rust.

If you want to read some geeky stuff about iron, and rust, read this.
Iron chemistry
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Old 07-05-2013, 05:25 AM
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Very interesting. I know that a electronic aspect is involved. It's amazing to see 50 years ago we put a man on the moon and we are still dealing with rust.I often wondered why these coatings systems even though they are airtight and moisture proof at the end of 20 to 25 year cycle they begin to fail or have failed pretty badly. Well thank you for bringing up that aspect. I did read the geeky stuff and towards the end I got lost.
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Old 07-05-2013, 08:11 AM
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I got lost way before the end.

The main point I picked up is that the presence of rust makes the remaining iron rust even faster. Minor points is this there are at least two types of iron oxide, FE2-O3 and FE3-O4.
The FE2-O3 is the red rust, the FE3-O4 is the black rust usually underneath the red rust. The red rust takes more space than the black rust, and once formed, is will lift paint enough to allow more moisture to get under the paint, and now the paint just keeps the steel wet longer, so more rust forms.

I have found phosphoric acid solutions remove the red rust pretty easily, but not so much the black rust. I have had pretty good luck with using electrolysis to remove both types of rust. the process is explained in detail here.
ELECTROLYTIC RUST REMOVAL (ELECTROLYSIS)

Iron rusting is a pain for us working with steel. But in the grand scheme of things, it is the affinity that iron has for oxygen that allows red blood cells to transfer oxygen from our lungs, to our cells, and the CO2 back to our lungs, so we can live.

Last edited by DanielC; 07-05-2013 at 08:19 AM.
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Old 07-05-2013, 06:51 PM
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As I said earlier I traveled up and down the East Coast for 20 years and the rustiest place on earth was Webster Florida. I would leave my displays out overnight and the rusty areas that had not rusted in years would have a fresh coat of rust in the morning.It had to be something in the atmosphere.A couple of interesting notes I have never seen the rust creep beyond the edge of the coating and 3 coats sprayed would level all the pitting in sheet metal. Bayer has developed a one coat poly urethane anti-corrosive system is now being used on the Marine Corps Museum.it goes on 6 to 9 mils in one shot. I got to check this out more closely.
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