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  #46 (permalink)  
Old 04-19-2014, 08:36 AM
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Some of these rust converters or snake oil products, as Shine calls them--and for good reason--have given the real thing a bad name.
Here is what PPG has to say about the best way of prepping the metal before epoxy

"Sand the bare metal areas completely with 80180 grit abrasive
Chemical treatment or the use of a conversion coating will enhance the adhesion and performance properties of the finished system."
PPG Refinish - Deltron®

A phone call could confirm, but I think what they mean is chemical treatment for signs of rust, or just conversion coating if no rust is showing.

================================================== ==

Here is what Dupont says

"For difficult to clean substrates, use appropriate surface preparation agent. (e.g. for aluminum, use DuPont 225S™ and for ferrous metals use DuPont 5717S"
http://dpcprd.asp.dupont.com/dpc/en/...9X0S_TDS_E.pdf

And of course 5717S is a metal conditioner, and difficult to clean substrates means rust.

================================================== ======

So as most professional painters will tell you, "follow the manufacturers recommendations" and I doubt that any paint manufacturer will tell you that it is OK to paint over visible rust that has been covered up.

IMO it is best to remove all traces of rust, then give the metal an 80 grit da finish. And as DBM has already stated--- even blasting doesn't remove all traces of rust, and abrasive cleaned metal will start rusting immediately.

================================================== ======

Some of the pros talk about chemical bond being much better than mechanical bond for paint, and they are taught that by the paint manufacturers.
Here is what Sikkens says about the metal under the paint.

"AutoPrep Pre-Treatment Wipes produce a conversion coating forming chemical bonds with metal surfaces enhancing adhesion and corrosion resistance"
Sikkens

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  #47 (permalink)  
Old 04-20-2014, 05:38 AM
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we've learned that epoxy is the best primer for bare metal.....but...every single paint manufacture has an etch primer ,and whats in an etch primer?phosphoric acid... I, along with about ALL the other pros have used plenty of etch primer without any issues but it needs another primer on top of it which requires more time and expense and its just not as good as epoxy....In my mind it makes more sense to clean my metal by scrubbing the acid in and thurohly cleaning it than just spraying on the acid on in a primer ,either way they need to be covered with primer anyways... that would make the etch primer obsolete.(useless)
Any of you guys that have done lead work ....or even soldered a wire or a copper pipe know that no matter how clean you get the metal by sanding, the solder wont stick until its cleaned with acid on a microscopic level. Granted epoxy and lead(solder) are completely different I just use this as an example of how clean is clean when prepping your metal
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  #48 (permalink)  
Old 04-20-2014, 06:42 AM
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i have no problem with phosphoric acid . i have used it since the early 70's . but when i switched to epoxy things changed .some cars i blast do not need it others do . i still use it but have to be diligent on how i use it . since the chemistry police are lurking we cant say neutralize any more so i will say rinse thoroughly while still wet . this will avoid any problems with the epoxy . the epoxy will still stick if not rinsed but only at about 60% and a possibility of other problems.
i have started using milkstone since a dairy friend here turned me onto it . the milkstone is 54% phosphoric acid where ospho ,navel jelly and such are around 15-30 % .so it will be cheaper once mixed with water or on bad rust used straight it will work a little better. the stuff the paint mfg sell is weak usually around 5%. good only for cleaning.

and a word of caution , paint mfg are in the business to sell you things whether you need it or not. the last place to seek advice is with a paint rep. follow tech advice but be cautious on product recommendations .

and the only thing you can convert rust to is a different color of rust .
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Old 04-20-2014, 10:25 AM
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Where did you get those percentages Shine? As I recall from checking several years ago, those two should be about the same % phosphoric acid, and PPG DX579 just a little less. I don't use either one because I got a deal from my local acid stripper on 5 gal buckets of his product and it has zinc phosphate in it also which is a rust prohibiter
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Old 04-20-2014, 10:39 AM
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milkstone is 56.33% phosphoric acid. ospho is 45% , naval jelly is around 15% . it's on their data sheets.
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Old 04-20-2014, 10:55 AM
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I started out originally using Sikkens wash primer (their etch primer) on my Mustang. At that time I just had the cowl and door jambs done after I stripped them. Etch primer is how I was taught. After I started seeing flash rust under the primer I said screw that, stripped it all off and that's when I first started using epoxy.
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Old 04-20-2014, 11:26 AM
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Etch doesn't provide moisture protection by its self, it has to be primed over.
You spiked my interest Shine, so I checked for MSDS sheet on Milkstone and found several different mixtures. A couple of them didn't even list phosphoric acid and the percentage of the ones that do use it varies, but the highest I found was 42%, and no zinc phosphate.

Some of the ones that I looked at were off shore from the US, maybe someone can straighten me out on this, but I would suggest to anyone trying Milkstone to read the tech sheets to see if you have what you want.
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Old 04-20-2014, 01:03 PM
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You wanna know what REALLY eats rust.......... Muriatic Acid.....cheap at Hardware stores in the Pool Supply section........Will eat steel also....but very slowly......It's good for reconditioning files...put a cap on a hunk of PVC Pipe and let em soak..........z
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Old 04-20-2014, 01:57 PM
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Muratic acid or hydrocloric is a strong acid and not something that I want to use as a rust remover. The fumes alone will corrode the metal if you just leave the lid off, and if you use it on your metal panels it will open the pores and make it very difficult to stop the rust later on. Works good if you are using it as a flux for body solder (lead), but otherwise I don't want it around.
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Old 04-20-2014, 03:10 PM
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Quote:
Originally Posted by zardiw View Post
You wanna know what REALLY eats rust.......... Muriatic Acid.....cheap at Hardware stores in the Pool Supply section........Will eat steel also....but very slowly......It's good for reconditioning files...put a cap on a hunk of PVC Pipe and let em soak..........z
never ever do this.
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  #56 (permalink)  
Old 04-20-2014, 03:11 PM
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Old 04-20-2014, 04:17 PM
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Yes I looked at that one, but it only has 42.25% by weight phosphoric.
http://www.stearnspkg.com/msds/bulk/...ACID-RINSE.pdf

Ospho has 45% by weight phosphoric
http://www.jamestowndistributors.com...PHO%20MSDS.pdf
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Old 04-20-2014, 06:40 PM
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yeah Shine, your stuff only has 42%. Ospho has a whole whopping 3% more.
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Old 04-20-2014, 07:14 PM
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Funny the gal says 56% on the lable . But it's only 12 bucks a gal here .
I only use it to clean on some things. My blasting rig get's it to white metal. Usually I just use dawn to get rid of oils .
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Old 04-20-2014, 07:16 PM
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I see it there on the label too....56.33%
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