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Old 03-31-2013, 07:06 PM   #1
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Rust converter (phosphoric acid) not working

I'm trying to fix a rust spot on my car cheaply and quickly, so it looks better when I sell it soon. I've read rave reviews about Ospho, which is mainly phosphoric acid, and lots of people recommended a generic version called Prep & Etch, which is only $15 at Home Depot for a gallon.

I bought the Prep & Etch, which is also phosphoric acid based, and brushed off the loose rust, cleaned it and applied the P&E. Just a small part of the rust spot turned black, but there was still lots of visible rust showing through. I figured that because it was a vertical surface, maybe it didn't stay wet for long enough and that's why it didn't work. So on another day, I cleaned the rust spot again, and put about 8 coats of P&E on it, spaced out over about a 30 minute period. Still the rust shows through, and the spot is still more orange than black.

I also tried the P&E on some rusty tools, and they too still appear rusty.

Did I get a bad batch of this stuff or am I doing something wrong? Others who have used this who've posted on other forums talk about the amazing results this stuff has on anything that is rusty.


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Old 03-31-2013, 09:53 PM   #2
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Always get what you paid for.
This one works.


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Old 04-03-2013, 08:51 PM   #3
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From experience working on older cars: I have used two different brands of this "Ortho" type rust neutralizers, and neither were big box store diluted solutions. Both of the solutions I have used plainly state something to the effect: "More than one coating of this material will not neutralize the rust better than a single properly applied coating." Maybe the stuff you buy at a big box store has been diluted way too much to work properly. Automotive paint stores carry the somewhat "professional" solutions and they are worth the pricing. I have used a brass bristled (fine bristles) brush to rub the solution in while it is still wet. Wiping off with something clean before it dries.
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Old 05-02-2013, 06:57 PM   #4
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I've had great success with POR-15 from an auto body supply shop. First, grind all rust out, then use the prep stuff for a few coats and let dry. Then apply the POR-15 for a few coats. It will turn black and stay that way as long as the area isn't forced to constantly sit in salt water. I treated the lower inner doorskins and lip of the tailgate of my old Ford truck then had it Ziebarted. 4 years later when I traded it in (should have kept it) no sign of rust anywhere.
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