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Old 03-06-2005, 01:03 PM
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phosphoric acid based rust dissolver

I've been stripping paint and rust this weekend and got to using the rust dissolver I bought last week. It works like magic but I can't seem the get the metal clean afterwards. I rinse the metal but when dry there is a streaky yellow/orange coating (streaking especially from rusted spots but covering everywhere).

I can sand through it easily enough when dry to reveal the shiny bare metal, but the solution is supposed to leave some kind of a coating to prevent immediate corrosion so I don't want to sand through this coating as I won't be painting it right away.

I just can't believe it is supposed to look like it does. It really looks terrible.

I have read through the thread 'the secrets of surface rust removal', and my metal doesn't look as clean as those pictures when I'm done.

What should the metal look like after using a phosphoric acid based rust dissolver? How do I get it clean?

Also, how clean does the metal have to be before epoxy primer? I am sanding using a DA and by hand, then using the rust dissolver. It's a lot of work, and the surface is clean, shiny and smooth, with some black pitted areas left after the rust dissolver. With enough hours I'm sure I can get it perfectly spotlessly clean, but when is enough enough?

I hope someone can help.

Rich

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Old 03-06-2005, 06:29 PM
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Ospho (phosphoric acid) converts the rust, as it does it's job it will turn black, and may require several applications. When treating sheet metal that is going to be painted I sand it all off, clean with metal prep, prime and paint as soon as possible.

Vince
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Old 03-06-2005, 10:38 PM
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phosphoric acid will not convert rust, it is in many rust converting products but it will eat it away not convert it in pure form.
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Old 03-07-2005, 12:18 AM
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So if the pitted areas that used to be rusted badly are clean now but black, I can primer directly over it?

I will go ahead and sand through all that nasty yellow coating then as well.

Rich
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Old 03-07-2005, 07:08 AM
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Quote:
Originally Posted by rlackey
So if the pitted areas that used to be rusted badly are clean now but black, I can primer directly over it?

I will go ahead and sand through all that nasty yellow coating then as well.

Rich
Re-apply your acid and wire brush the area as many times as it takes to get all the "black" removed.
In heavy pitted areas this may take as many as 20 iterations to get rid of all the rust. If any holes in the metal show up, weld them or fill with lead. Then sand with 80 grit and prime with epoxy primer.

Roger
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Old 03-07-2005, 07:14 AM
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Roger,

Thanks for the advice. I will be working on it again this evening after work. I'll reapply until I get rid of it all.

Rich
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Old 03-07-2005, 08:26 AM
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Phosphoric acid converts the iron oxide (rust) to iron phosphate which is very stable. That coating on the steel is iron phosphate which is a good base for primer. It is working just as the chemists designed it!
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Old 03-07-2005, 11:44 PM
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Quote:
Originally Posted by roger1
Re-apply your acid and wire brush the area as many times as it takes to get all the "black" removed.
In heavy pitted areas this may take as many as 20 iterations to get rid of all the rust. If any holes in the metal show up, weld them or fill with lead. Then sand with 80 grit and prime with epoxy primer.

Roger
That's right Roger, the only thing you want to prime over is clean shiny bare metal. Those black pits will come back and bite you.
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Old 03-08-2005, 12:44 PM
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Well, I don't want to get bitten, that happened to me once already which is why I'm doing this one myself.

I have an all original '59 VW Beetle that is my daily driver and I had it stripped and painted about two years ago. Within a year the rust started bubbling up under the paint. I couldn't believe it!

Now that I'm stripping the Chevy, I am learning just how much work it is to get every little bit of rust and paint stripped. It's hours and hours of work, and I'm getting to know every little nook and cranny of that body like the back of my hand.

So I'm not looking for shortcuts because I think shortcuts are the reason I have to strip down the VW again as soon as the Chevy can take over the daily driving for a while.

I managed to sand off the yellow coating left by the rust remover from the weekend and I was pleasantly surprised to see it was indeed providing at least some measure of protection. The bare untreated parts start rusting again after two days exposure to the sea air here in Cape Town, maybe less, but under that ugly streaky yellow coating was shiny metal.

So, I think I'm going to end up reapplying a few more times to take care of the heavily pitted areas, but I should be ready for primer before too long.

I am sure I won't regret all the hard work I'm putting in now when I still have a spotless paint job five years down the road.

Thanks all for the input!
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Old 03-08-2005, 07:17 PM
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Use quality primers and paint and it should last 20+ years with proper care if the corrosion is removed. Bob
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Old 03-10-2005, 09:29 AM
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I'm getting conflicting information from this thread. I was treating a hood last night that had an even coating of rust on it. (Almost looked like primer). I sanded it all smooth as much as possible with a scotchbrite before I attempted spraying on a phosphoric acid based rust killer. Rust Cure to be exact. Anyway, the only part that ever blackened as some deep rust pits in a few areas. I was expecting it would turn the whole thing black, but instead it now just looks like wet rust. Its a dull reddish color. What should I do now? Sand it down and treat again?
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Old 03-10-2005, 10:09 AM
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Quote:
Originally Posted by FrankR
I'm getting conflicting information from this thread. I was treating a hood last night that had an even coating of rust on it. (Almost looked like primer). I sanded it all smooth as much as possible with a scotchbrite before I attempted spraying on a phosphoric acid based rust killer. Rust Cure to be exact. Anyway, the only part that ever blackened as some deep rust pits in a few areas. I was expecting it would turn the whole thing black, but instead it now just looks like wet rust. Its a dull reddish color. What should I do now? Sand it down and treat again?
Yes, I would power wire brush it versus sanding it at this point. Then put another coat of your rust remover on. You will be able to tell while you are putting it on if there is any rust left in the pits. Do it over and over untill you are sure that all the rust or black spots in the pits are gone. Wipe it down with thinner or reducer then do a final sanding with 80 grit, treat with metal prep and put on your epoxy primer. Then coat it with a urethane primer-surfacer.

Roger
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Old 03-10-2005, 02:14 PM
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FrankR, I don't know if this will help, but my whole body was (and some still is) covered in the kind of rust you are dealing with on your hood, maybe even worse.

Before even attempting to apply the rust dissolver I sanded as much of the panel right down to shiny bare metal as I could using a DA and by hand. I found that on many panels there seemed to be a lot of the original black primer even under the coating of surface rust, and I had to get through that in order for the rust dissolver to really take effect on the metal underneath.

I am no expert but from my experience I don't think rust dissolver alone can ever replace sanding as much of the rust and paint/primer off as possible first. I rely on the rust dissolver only to treat the pitted areas and to get the sanded panel clean of all and any corrosion left before filler and primer.

It sounds to me like you might want to go at that hood with a DA and get as much of it right down to the metal as you can, applying the rust dissolver afterwards to remove anything left. I'm not sure that a scotchbrite will do it.

Roger is right, if the rust isn't too heavy wire brushing should also work, but I prefer using a DA. Roger also mentioned it can take quite a few applications to get it all.

I've never used the spray, but a thicker brush on rust dissolver or naval jelly might also work a bit better.

Hope this helps, I feel for ya! It's a lot of work!

Rich Lackey
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Old 03-10-2005, 02:48 PM
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The reason for recommending the wire brush is that it will get down into the pits better than sanding.

Roger
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Old 03-10-2005, 02:54 PM
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Roger, you are quite right. A stiff wire brush will do the trick where sanding won't. I didn't mean to sound like I was contradicting your instructions, using the right tool for the right job is half the battle and I'm learning from you guys all the time.
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