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AydinZ71

Rust converter (like rust mort)

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I have both rust mort and por 15 metal prep. They both say to rinse the product off after a time. I’m confused... when I follow the instructions I immediately get surface rust from the water before I apply primer. Is this normal? It seems you would want to prevent re-rusting the surface with water? 

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Posted (edited)

I know exactly what you mean...

 

I was going to use POR-15 in a few areas on my project, but their TDS was insistent that I had to first use POR-15 metal prep, and rinse it off with water, before applying the product.  I knew that would be a horror-show of flash rust, so I just used another product (Rust Bullet).

 

Maybe POR-15 is designed to work best over a layer of surface rust?  Or maybe the company is just greedy and wants to sell as much prep as they do POR-15?  I'm not going to try it.

Edited by Ironhead

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Both por15 metal prep and Rust Mort use Phosphoric acid to convert the iron oxide to iron phosphate, Rust Mort has some thickener in it so it stays wet longer but the are essentially identical.  You can't let the product dry on the metal or you will have to re-coat it with the  phosphoric acid solution to remove the white powdery layer then it has to be washed with water, hot water is the best.

Then dry it as fast as possible, wipe off most of the water with a clean cloth, compressed air or a paint stripper heat gun.

Then prime it or paint it immediately, if you see white powdery areas don't bother painting it, you need start again. 

It doesn't matter how many layers of paint you spray on it you will never cover that efflorescence.

 

I have had such mixed results with phosphoric acid that I don't use it anymore (anybody want a shelf full of phosphoric acid products?)

Now I use citric acid, much less toxic, doesn't stink, very cheap if bought in quantity, it takes a little longer but after it has removed the rust and is washed it doesn't rust as quickly, it also won't burn you if you get some on your skin, just wash it off. 

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Fascinating! So applying epoxy primer over the "flash rust" is OK? I'm using 2k epoxy primer from Speedokote. Seems to have great reviews, and has gone on easy. Time will tell.

I been using both Phosphoric acid products since I cant get all the nooks and crannies. Some of the deeper scratches are also hard to de-scale without removing metal (which is already super thin). 

 

Edited by AydinZ71

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it sounds like a bad idea to me too... what should I do? I metal needs to be etched and treated for the minor rust in the sanding scratches that are not accessible. I still dont seem to have a solution.

 

I did call POR 15 (not a 2k epoxy), and they said the flash rust is normal and their product is intended to go right over it. 

 

I suppose the fundamental issue at hand is this: its impossible to completely degrease bare metal and leave zero film, while still preventing flash or surface rust of some kind. I mean, its kind of an oxy moron isnt it. Bare, degreased metal rusts almost immediately with my 50% humidity. 

 

PS: Shitty datsun steel doesnt help

Edited by AydinZ71

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I wire brush, sand, or Scotch Brite the metal to a clean state, with no rust, clean/degrease with Prep All (made by Kleanstrip), then epoxy prime.  The only thing I would caution, is that Prep All doesn't work well with water soluble oils, like if you sweated or drooled or rubbed your greasy hair on the part.  To clean that stuff off I use a little bit of Westley's Bleche Wite on a rag or paper towel before the Prep All.  The Bleche Wite is basically just a very strong detergent, so I make sure I remove all traces of it with a damp rag then immediately blow the part dry.  Prep All evaporates and leaves no residue.

 

I have no doubt that you can apply POR15 over flash rust, since it is designed to go over rust, but it seems like the height of silliness to create rust for it.  And epoxy primer is not designed to go over rust.

 

I guess I am lucky in the sense that Nor Cal is a dry environment and I have had no real problem at all with flash rust, even after working with bare metal for three years.

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Ok. I think I have an idea of what to do next time. I have read some people using acetone or laquer thinner to remove the phosphoric acid. I think this might be a better choice, since acetone will not leave a residue, and should remove the acid. Il give it a try next time! 
 

i know you can’t just leave the acid on there. It will turn to a white powdery salt of phosphate, and interfere with adhesion. 

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17 hours ago, AydinZ71 said:

I think this might be a better choice, since acetone will not leave a residue, and should remove the acid.

There is a reason why every rust product that has phosphoric acid in it says " wash with water".  You can use acetone to displace the water once it has been washed, you can also use methyl hydrate(wood alcohol).

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I really question whether the POR-15 metal prep is absolutely necessary, or just another product they want to sell.  I used to use POR-15 on small parts that I fabbed for various projects, simply because it is pretty much as tough as powder coat but you can do it at home.  These were not rusty parts, just clean metal that I lightly sanded to scuff, cleaned with brake cleaner, then coated with POR-15.  It worked fine without their metal prep step.

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18 hours ago, grannyknot said:

There is a reason why every rust product that has phosphoric acid in it says " wash with water".  You can use acetone to displace the water once it has been washed, you can also use methyl hydrate(wood alcohol).

 

Thanks for the tip!

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I have been looking into Tamco Paint who offer a compete line of painting products.  Their epoxy and primers have rust inhibitors and also have "rust encapsulator" product called MonoCoat.  Here is a YouTube video of product which I found very informative.  Check out some of Tammy's other videos explaining other products Tamco offers.  Have not used their coatings to date but decided use them exclusively on my current build from primers to clearcoat.  FYI, they usually have a 30% sale at end of November from what I gather so it maybe good chance for anyone to experiment with Tamco products like me.

 

 

 

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7 hours ago, 280Z-LS3 said:

FYI, they usually have a 30% sale at end of November from what I gather so it maybe good chance for anyone to experiment with Tamco products like me.

That's good to know since I have a 510 that needs paint this winter.  Tamco gets very good press on https://www.autobody101.com/forums/index.php?sid=f044bf1f351a02abe241234902095df9

there are a number of professional auto painters that answer questions on that forum.

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I use a product called master coat. I cant speak to how well their paints work (same kind as por15) but their metel prep has zinc phosphate in it which is embedded in the metal as the rust is converted (or so they say) I wiped my engine bay down and left it for a year in Washington state (very moist) and didn't have any issues. I believe they also say to wipe it off with water prior to paint but the extra protection from the zinc prevents flash rust.

 

The reason you need to wipe it down with water is to rinse the acid out and to neutralize it. Water is ph neutral, dont know about acetone. 

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So far I have to say I have been pretty impressed with Rust Bullet.  I am not using it on rusty spots, rather just brushing it into seams and what not where it will be difficult to spray in epoxy.  I did a bunch of testing before using it.  It dries rock hard in 24 hours, and the adhesion to clean (not rusty) and fairly smooth metal is absolutely unbelievable.  It also dries to a slightly "flat" finish so epoxy sticks well to it without scuffing.  With a slight scuffing, the epoxy sticks so well to it that it's never coming off...

 

How well it encapsulates and "kills" rust, I cannot say.  But it sure seems like it will effectively prevent rust from forming.

 

Best of all, no acid prep or rinsing with water is required.

Edited by Ironhead

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3 hours ago, JMortensen said:

FWIW, I used Rust Bullet and scuffed and prepped and it did flake off in fairly large flakes. Could be my prep wasn't up to snuff, but I'm no longer a fan.

 

I don't know what to think of that.  I did an adhesion test, where I cut criss crossed lines with a utility knife all the way through the RB and into the base metal, leaving a grid of small roughly 2-3mm squares.  Then I burnished on a piece of Gorilla double adhesive duct tape over it, and pulled it off.  Nothing, not one little square or even a corner of a square, lifted off.  This was on clean, lightly scuffed metal...no rust...

 

What was your substrate?

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