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Topic Review (Newest First)
03-27-2017 06:41 AM
Originally Posted by Big Truck Driver View Post
What is a good procedure in using ospho under epoxy?
Wipe on , keep wet for 15 minutes. Wipe off with clean towel only,no water, let dry and paint?
Or do you wipe off damp cloth then again with wax grease remover then paint.
It depends on what your trying to do, if you have rust or not or if your just trying to protect the bare metal from future rust.
As a metal prep Ospho can be deluted a lot. You just add about 50% water. Using a plastic pump spray bottle you spray it on, SCRUB it in (scuff pad) then wipe it off with a damp paper shop towel, youll see all kinds of dirty crap coming off your supposedly clean metal. OR you can do what most of the pros do and just spray your epoxy over the bare metal without doing anything and save a few hours. Its good enough for them.
Either way you go always clean with W&G You wouldn't believe how many pros don't even use this on bare metal prep. Also keep in mind not to touch your bare metal without gloves the oils on your hands will start rusting anything that's been touched, even under the primer.
Doing all this is still useless if your compressor is blowing water and oil out your hose, good filters in your air supply are important
03-26-2017 03:11 PM

The tech at SPI said wipe with a damp cloth enough to make sure the acid has been neutralized. He also told me using Axalta or PPG metal prep and conversion coating was better yet. He compared it to overkill, but I'd rather be sure the acid's neutralized than take a chance.
03-26-2017 02:58 PM
Big Truck Driver What is a good procedure in using ospho under epoxy?
Wipe on , keep wet for 15 minutes. Wipe off with clean towel only,no water, let dry and paint?
Or do you wipe off damp cloth then again with wax grease remover then paint.
03-23-2017 08:23 AM
deadbodyman Theres never been any doubt that phosphoric acid/Ospho works great at removing rust and keeping it gone and also keeping bare metal from rusting.
All the controversy has always been about the paint/primer prep because if the treated metal isn't prepped right the primer wont stick well or will bubble up on you. Even though Ive used it a long time and know how to use it, all this controversy has made me respect the products use much more. I always pick a few spots after its primed and cured and check adhesion by sanding down to the metal, carefully checking how well the metal to primer edge feathers back, it should feather back smoothly without any broken edges. After that I'll try scraping it off in a few spots with a razor scraper if you can scrape it off the metal fairly easily youve got a problem. it will scrape off in little chips but it'll be very difficult and break many blades.
Once you have the proper prep down you'll be able to use Ospho with confidence as a rust remover and metal prep.
As a metal prep on old metal theres also no doubt how well it cleans. Many times Ive prepped metal for epoxy without using ospho by sanding followed wax& grease remover (solvent and water born) then used ospho on a small spot and couldn't believe how much dirt and grime it got off my prepped work.
Ospho is a great product but respect it, prep carefully and always check adhesion once the epoxy is cured and BEFORE moving on, if you screwed it up that's the time to find out NOT after it all painted.
03-13-2017 07:55 AM

Yeah, I was thinking after I typed that it looked wrong. I've used vinegar to remove rust and a base wouldn't do that. I got the impression from SPI that they originally marketed to "rusteration" shops an amateurs (like me). I guess the quality of their product brought it to the attention of professionals? Anyway, I was lucky enough to apprentice (work for parts) to a guy who had amazing tallents. mechanical, sheet metal, and paint. He did some extremely nice restorations of American and foreign cars as well as historic race cars. 1 thing he did use was Extend on rusted metal after wire brushing or sanding/grinding the loose stuff off. It actually did work. A friend did the bodywork on his car at my mentor's shop, I did the final paint work at my motorcycle shop. I'm still in contact with the car owner who told me 10 years later the bodywork and paint looked like the day we finished it. He sold the car after 10 years, so have no info past that time period on how long it lasted. It was finished in Centari over Corlar epoxy primer.
03-13-2017 06:24 AM
deadbodyman Ive heard of using vinegar to etch metal, but not neutralize, vinegar is an acid also.
The funny thing about all this Ospho (acid rust removal) is it all started because SPI had written Do Not Use acid products with their epoxy primer and I had stated that Ospho works very well with SPI epoxy. and ANY other primers for that matter. That's when all the so called "experts" jumped in saying not to ever use ospho and ignorant crap like that. Well its been a few years and now SPI has removed that part of the label and started recommending HOW to use ospho successfully to remove rust. Its simply amazing how something so simple to use gets used wrong by so many people and causes problems. If you refuse to read or follow directions OR have problems making a peanut butter sandwich then stay away from Ospho its that simple

Converting rust is never a good idea, so I wont even get into that.

Im no expert either but I have been doing this work and using Ospho professionally, for around 35-40 years so I have an idea of what works.
03-12-2017 12:13 PM
Morpowr I realize this is an old thread, not sure anybody still reads it. I don't claim to be anything close to an expert, and I may have missed something in the thread but I see a lack of mention of Conversion Coating being applied after using Metal Prep. Axalta (DuPont) & PPG both sell this product and a tradesman I trust used this on his restoration paint work. When I spoke to Tech Service at SPI he discussed Ospho and following it with water, but when I mentioned Metal Prep and Conversion Coating he told me that was superior to Ospho followed by water. Based on my conversation with him the Conversion Coating neutralizes the acid. I've also seen some older painters use vinegar to neutralize, but have no experience with that.
06-23-2015 03:30 PM
Camaro Z_man check this out....
04-23-2014 05:03 PM
Chevymon I'm sorry you feel that way Shine, you have some good paint advice to give and it would be a loss if you leave the site.

At the same time, I think that we all need to be ready for a challenge, so that our information will be the best that we can give. With the price of products today, I for one do not want to be responsible for someone making a mistake.

JFTR, I have been using phosphoric for 25 years, but I wasn't familiar with the data sheets on these two, so the links that I posted were the MSDS sheets, its just to show where the info came from , and make it easy for anyone who wants it. Because if you are going to play with fire, then you need to know how to control it. Its not rocket science but it is chemistry, and not being a chemist, I need to be able to find accurate information.

If it turns out that we don't see you anymore, then thank you for the info on Chemical Guys, I may to try it. Be well, Shine.
04-23-2014 07:48 AM
shine this is the last time i'm going to post on this site. but here is my " opinion "
new guys come here for advice. it's the paint and body section. their hope is to get some help from experienced paint and body tradesmen .
but what they get is confused by all the google experts and wannabe's trying to make rocket science out of cleaning metal . or my favorite , use battery acid on it . the best advice i could give them is to see how far away from this place they could get. i've seen more bad advice than good here lately. i did not come here 10 years ago to win a popularity contest i came here to interact with tradesmen . but i have watched them leave one by one . there is a point where it is just a waste of time . i'll argue with a tradesman all day long because at the end of the day one of us is going to learn something . but arguing with paint salesmen or google experts gets me nothing .
i truly hope these new guys ignore this entire thread .
04-23-2014 07:31 AM
Chevymon OK, here is my opinion, and it is just that----an "opinion"
The label does say 75%.

But it goes back to what I was talking about before, you can not trust labels.
If you look at the data sheet (MSDS), it says that information is not available.


As I have said before, I'm not a chemist, so correct me if I'm wrong.

When I look at the MSDS for Ospho it's a different story.
In bold letters, it says PHOSPHORIC ACID SOLUTION (75%)

It makes me wonder if that is the reason for the low cost of Milkstone. They don't have the expense of the rust inhibitors, or have to worry about paint adhesion, so maybe they can get away with a weaker phosphoric solution to start their formula with.

The only other ingredients they list are cleaners for the milkstone, and liquid (containing phosphoric acid), so its possible that they could end up with a 42.25% phosphoric even though the original phosphoric solution is less than 75%. I think they probably just get a solution to suit their needs, whatever makes it come out to final solution percentages they want.

You can't really call this a "snake oil product" because they don't make any claims about rust removal, its all about cleaning milkstone as the name implies. So I would suggest a product formulated for rust removal.

Here is another reason for reading the data sheet

So don't try to neutralize phosphoric acid. All the data sheets seem to say the same thing about taking the acid off, JUST RINSE IT OFF WHILE IT IS STILL WET. I rewet it with acid before rinsing, to make sure some of it hasn't started to dry. In that state is still looks wet, but will be a little sticky, and thats not good for a complete rinse. Actually, I use a scotch brite pad wet with acid to scrub it just before rinsing, and that does a pretty good job of getting rid of it.
04-22-2014 06:40 PM
Lizer Yep I saw that when I went back and looked again. A bunch ado about nothing.

[color=gray]Sent from Free App[/color]
04-22-2014 06:35 PM
Old Fool
Originally Posted by Lizer View Post
That's a good catch. I initially just assumed you were looking at a different tech sheet than the product Shine was talking about.

The way they have it stated/labeled is completely assinine. It's actually wrong. I'm a microbiologist converted to biochemist and have to make these calculations every day, but if someone like a junior scientist would pull something like this on me I'd be upset because it would really throw off my acid molarity. That's why I always double check their work.

If they were starting from an absolute stock, say pure crystalline phosphoric acid, they could achieve the 50-something percent, ie weigh out 56 grams and Q.S. to 100 ml with DI water. But here, when they're stating 56%, they're actually starting with a stock solution that's only 75% (I looked and 85% is the max solubility in water). So like you are saying, it's really 56% of a 75% stock, which brings you to the 42%. It works out the same if you use the C1V1=C2V2 formula which is what I use for calculations.

For the none chemistry types, take a cup of coffee that is 75% coffee grounds (eww). Now take a little bit of that and add it to a second mug so it's 56% of that mug volume, with water making up the rest of the volume. Now let it sit on the counter for a few days so the water evaporates. Assuming a 100 ml volume of coffee originally, you'd have 42g of grounds in your cup.

Bottom line, 42% vs. 45% as a discussion point is meaningless. They're practically the same.

But stating 56% phosphoric acid as an active ingredient is wrong, unless it stated on the front label it was 75% phosphoric acid stock and I just didn't see it.

Good eye

They do state a 75% solution on the label:
04-22-2014 11:19 AM
Lizer The milkstone is obviously working for Shine, or he wouldn't be using it. Milkstone active ingredient= phosphoric acid.

Ospho active ingredient=phosphoric acid.

Phosphoric acid is phosphoric acid.

The ensuing chemical reaction doesn't care what color bottle it comes in, or what the label says.
04-22-2014 07:18 AM
Chevymon Shine, please don't take this as a personal attack, I'm just expressing my opinion on the product, and I probably could have thought more about my approach. I guess its just not as easy to be polite and respectful with the pen as it is in person. Life is too short to be making other people miserable, and that was not my intention.

But this is a discussion forum where a lot of people come to get information. I don't think anyone knows it all, and I sure have my fair share of failed attempts at doing this or that, so if you guys disagree with any of my posts, I hope you point it out so others can be spared. And I will not take it to be an attack on me personally, and that is certainly not what I intended to do to you either Shine.
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