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Old 06-26-2013, 12:34 PM
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Black over black and the rust comes back

Often the question comes up should I strip the primer off replacement panels. This primer is usually black. It's a difficult question. If the metal had any type of rust and it was primed over at the factory usually in Taiwan it will bite you later.This is a picture of floor pan that was painted over with black moisture cured urethane over the black factory primer about five years ago.The AC drain leaked under the carpet and caused it to rust beneath it.How did that happen , that rust would form under the coatings? The answer ,black is not airtight, the silver should have been used first, then the black.Has anyone else experienced this problem?
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Old 06-26-2013, 01:48 PM
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This is one of those things without a LOT more info it is pretty much worthless to even think about. If the metal is completely coated in about any automotive primer and paint it likely isn't going to rust. If it is coated with something sub-par like an aerosol paint that is very thin, then it will rust even though being fully coated. But more often than not the coating hasn't much to do with it, because the moisture gets UNDER the coating, at an edge, at a chip, at a worn spot, it gets under the coating and I don't care what you have on it, it will rust.

What exactly happen here, by the photo who knows.

Brian
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Old 06-26-2013, 03:07 PM
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Thank you for the explanation
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Old 06-27-2013, 05:11 AM
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In the areas where there would be chipping, abrasion or being scratched by fasteners and industrial primer would be required. There are primers that even when scratched the rust won't go beyond the scratch Due to a blood clot I have been working with the body man that has been in the business for 45 years. Some of the systems I showed him and we used he just can't believe.
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Old 06-27-2013, 07:50 AM
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Sure there are products that resist that moisture from getting under it more than others.

Brian
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Old 06-27-2013, 08:15 AM
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Look's like this might just be leading up to something..
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Old 06-27-2013, 08:59 AM
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Well there are a lot of people that put black moisture urethane over rust so I initiated this new thread to clarify what happens when you do this. I would like to share some knowledge about other types of industrial coatings that can be useful in prolonging a standard auto body paint job. This is what motivated me to start the Masters series line.If you look at our photo gallery you will see Vintage cars of Fort Mill South Carolina priming everything with the silver primer.they started doing this 20 years ago because cars left outside waiting to get into the shop for years didn't rust with this primer. So there are many options in many different types of paints that a lot of people have never seen or heard of and can be very useful. I didn't start this topic for debate I started it to inform.
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Old 06-27-2013, 09:08 AM
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Quote:
Originally Posted by Pats55 View Post
Well there are a lot of people that put black moisture urethane over rust so I initiated this new thread to clarify what happens when you do this. I would like to share some knowledge about other types of industrial coatings that can be useful in prolonging a standard auto body paint job. This is what motivated me to start the Masters series line.If you look at our photo gallery you will see Vintage cars of Fort Mill South Carolina priming everything with the silver primer.they started doing this 20 years ago because cars left outside waiting to get into the shop for years didn't rust with this primer. So there are many options in many different types of paints that a lot of people have never seen or heard of and can be very useful. I didn't start this topic for debate I started it to inform.
Sounds like your leading up to your Masters series line to me.. I hope I'm wrong..
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Old 06-27-2013, 09:42 AM
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Sounds like to me your guarding your turf. You can buy industrial coatings in a number of places. Some companies will sell to you, others won't. That's why I usually use generic terms. I know that I shouldn't say the word Mastercoat on your forum. I hope that you and your friends won't gang up on me and hurt me like before. FYI I don't receive any money from mastercoat,I did this to share information.
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Old 06-27-2013, 10:26 AM
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Quote:
Originally Posted by Pats55 View Post
Sounds like to me your guarding your turf. You can buy industrial coatings in a number of places. Some companies will sell to you, others won't. That's why I usually use generic terms. I know that I shouldn't say the word Mastercoat on your forum. I hope that you and your friends won't gang up on me and hurt me like before. FYI I don't receive any money from mastercoat,I did this to share information.
No..I would never gang up on you as you say..
As far as guarding my turf..That's funny... I just try to follow the rules when at someone esle's house... If you think by ganging up on you because we like SPI,, That's even more funnier.. And if that's what you think this is all about,Your wrong..

I asked you a simple question...
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Old 06-27-2013, 10:51 AM
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I'm glad we cleared that up. Now how about we get back to why you shouldn't use black moisture cured urethane by itself.
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Old 06-27-2013, 11:07 AM
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The photo I posted shows the rust under the coating.the rust was caused more by oxygen than moisture. Take a cardboard shirt box and paint the inside with the black moisture cured or the clear. Fill it up with water and it won't leak it's completely waterproof. If you were to take that clear moisture cured and painted it over clean steel within a couple of months you would see rust growing under the coating.
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Old 06-27-2013, 12:03 PM
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Don't some of them parts come with a E-Coat of them ???

That picture you posted don't even look like someone sanded it before it was primed,,,

Brain hit the nail right on the head.. Who know's how the person did the priming......A lot of things come into play when you put the first coat on bare metal..To me.. It's the most important coat you will be spraying..

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Old 06-27-2013, 12:36 PM
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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.
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Old 06-27-2013, 12:53 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 am with you Pat, but the junk pretend "E-coat" (faux-coat ) applied over cheap bare mild steel at some overseas plant is a hell of a lot different than REAL "E-coat" Electrophoretic coating that is applied on OEM parts that are even galvanized before the e-coat! Every single part of every single car made the last number of decades is galvanized, fenders, frames, everything!

To tell people to remove E-coat is going WAY over the top in my opinion.

Now, I want to learn something, this interests me, if some cheap primer is over a flash rusted piece of mild steel floor pan and THEN it's fully coated with an epoxy primer, then urethane automotive 2K paint, how does it BEGIN to rust if it is COMPLETELY covered? Let's for the sake of discussion there are no chips or thin spots or anything like that, because THAT is where it going to start. But let's say there is nothing like that. The epoxy primer is a full 3mils and the paint is 4mils, fully applied over the entire piece. How can it rust?

Brian
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