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Topic Review (Newest First)
Today 01:57 PM
Chevymon 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.
Today 01:03 PM
zardiw You wanna know what REALLY eats rust.......... Muriatic 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
Today 11:26 AM
Chevymon 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.
Today 10:55 AM
Lizer 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.
Today 10:39 AM
shine milkstone is 56.33% phosphoric acid. ospho is 45% , naval jelly is around 15% . it's on their data sheets.
Today 10:25 AM
Chevymon 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
Today 06:42 AM
shine 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 .
Today 05:38 AM
deadbodyman 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
Yesterday 08:36 AM
Chevymon 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"

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"
04-18-2014 09:58 PM
DanielC I have to agree with DBM on this. In my experience, you can sand off surface rust, wire wheel it, aggressively scrub with a stiff stainless steel brush, and ospho, or any other phosphoric acid solution, and have what is generally considered treated, or converted rust. the black or very dark colored stuff.
If you take a small carbide burr, on the black stuff, in the bottom of the pits, or wire wheel it again, aggressively, you will find red rust under the converted black stuff.

Rust is an electrolytic reaction. Take two different metals, put them in an acid solution, or a base solution, or a salt solution, and connect them to each other, one metal will be eaten away. Once steel starts to rust, you have the two different metals. The rust, and the non rusted steel. Add moisture and the rust feeds itself on the bare steel.
04-18-2014 08:33 PM
deadbodyman Ospho does leave a protective film, that's the main reason I use it, so my bare metal does not rust...
Ospho does remove rust but it also converts rust {I don't convert I remove it) however I do believe converting it on microscopic level is a good thing...So even if I media blasted I'd be using Ospho...
I'm going to go out on a limb here and say I truly believe that even if you blasted the rust off, using Ospho is a better way than blasting and just priming.. Otherwise I wouldn't still be talking about it after all these years...I understand that others have had some problems and its always adhesion problems related to the way the metal was prepped prior to epoxy...Sure the simple cure is NOT To use Ospho if you don't want to take the time to do a proper prep simply epoxy over the bare metal and no adhesion problems...but your just swapping out adhesion problems for rust problems sometimes in less than a year...
Here's something you can try that always impresses me. sand some metal with 80 until you think its clean and ready to prime...then get the metal nice and wet with Ospho and scrub it in good with a red scotch brite and watch how much dirty grime comes off that metal that you thought was clean...
After the Ospho drys 24 hrs sand with 80 and then 180, I even go to 320 sometimes because after sanding with each grit it looks better and better ,theres no doubt which is cleaner just 80 grit or Ospho and 80-180-320,its like night and give it a try and you decide whether or not its worth all the extra work.....Its only a foundation...
I have changed my procedure slightly now I use both water born AND solvent based Wax & grease removers before my epoxy ,I really like this waterborn stuff SPI has now...
To put this all in a nut shell,I think If there wern't any scary adhesion problems everyone would be using Ospho without a second thought just like I do.
04-18-2014 09:13 AM
zardiw That master stuff only lasts a year......RustX has lasted many years on parts and other things I've applied it on.

The thing with rust removers, sand blasting, etc is that steel will start to rust when you paint what you think is clean steel, that rust will eventually increase under the paint, or on the sides, and you will be back where you started.....

Makes a lot more sense to turn the rust into a protective coating that will never rust again.......

04-17-2014 09:27 AM
Originally Posted by TARM View Post

What I have gathered from reading everything here is the following:

I see little controversy on here that Ospho does a good job of protecting or converting rust.

It seems the main and really only point of contention is whether Ospho leaves an acid film or not. LOL
I think that most here will agree that converting rust is not a good idea, what you want to do is remove rust. And some, if not most, will agree that phosphoric acid is a good way of doing that, but the point of contention from the paint manufacturers is only that it be thoroughly rinsed off. In fact a lot of them have an epoxy that is recommended to be used after metal prep, for better adhesion.

SPI does not recommend using a metal prep, but they do say its alright if you know how to paint prep the panel after its use, which does not include neutralizing in the technical sense.

This part that I posted earlier in the thread was cleaned by blasting then phosphoric acid and rinsed. This has been zoomed in quite a bit, the raised part at the bottom is actually only 1 1/2 inches wide. I have found that if I agitate the the thoroghly wet acid on the panel with a scuff pad or brush just before rinsing, it comes off like this. This was badly rusted as you can see by the pits.

04-16-2014 07:18 PM
Old Fool If you have your heart set on using a rust prep type product I would suggest you check out MasterCoat products. They have a very impressive product used on subway cars and bridges and holds up quite well.

This is the only system that I would trust other than abrasive blasting and epoxy.

Click here for MasterCoat System
04-16-2014 10:06 AM
zardiw The best rust converter is Rust-X. Have used it for years and it works like a charm. Good idea to paint over it afterwards:
I have also poured about a half 16 oz bottle into the radiator. It will convert all the rust inside the engine.....Probably a good idea to flush it afterwards since it is a weak acidic solution and could have an effect on aluminum parts.........I've poured it on aluminum and there does not seem to be any it's probably OK to leave it in, since it will be very diluted anyway.

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