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How to neutralize Ospho

Barry

Paint Fanatic
Staff member
#1
The ONLY acid cleaners SPI recommends is Opsho, PPG and DuPont metal preps as long as their instructions are followed to a tee.
Use any other system you want, just do us a favor and use no SPI over them.

There can be NO shortcuts for good results.


Ospho, is a great product for automotive if used right, we give scare warnings because we want people to call so we can make sure they know how to neutralize it, so no problems will arise.
Only one way to use and here it is:

Use as needed and apply as many times as needed to get the spot clean
, let dry and leave for months if you want, don’t matter.
To neutralize the Ospho MUST be wet, so if dry, re-wet with itself and let set one or two minutes and with a clean rag and water, wipe off like washing the car and then dry.
Next, then da car with 80 grit, clean with 700-1 wax and grease remover, let set an hour and coat with an epoxy.

Notes of interest (maybe)
If you try and sand dry film off you will lose 40-60% adhesion (per adhesion tester as some will embed itself in metal and amount depends on how long the Ospho has been on panel as we do know acid films degrade with time but due to many factors we cannot pinpoint a time frame.
The tape is not a test, use razor scraper after 7 days or an adhesion tester if you have an extra $6000 to spend.
How does it fail? Here are a few calls.
Washing car and hose bounced up, hit car and paint bubbled.
Kids finished ball game
and ran by car and tossed ball gloves on hood, next day two big bubbles.
Wife got bag out of trunk, closed trunk and set bag on truck
to play with keys, next day a bubble there.

My FAVORITE TECH CALL at least once a month, my body filler dried and sanded great but when I got to metal is was gummy, DO I HAVE A BAD HARDENER? Nope only one thing, you applied it over an acid film..
 
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#2
i have no pity for them any more barry . for over 10 years professional painters have been trying to tell folks this but they still do it then want someone to help fix their screw up . ospho is the worst because of their dismal tech advice. they continue to give bad advice to restorers . ok if your painting oil tanks with alkyd enamel but even lacquer did not like acid. every paint mfg that sells a metal prep explains how to rinse while wet but still people think they are smarter than the chemist who make it.
phosphoric acid is one of the best cleaners for bare metal but can create a complete disaster . i wont even recommend it any more because folks just wont follow the steps.
 
#4
My grandfather used ospho on every piece of metal on every horse carriage he restored and I don't know of any problems he ever had. But that was oil base enamel and mostly synthetic enamel. We never washed it off with anything but mineral spirits. We took everything to bare metal ospho, primer, filler, primer then paint.Now on a car and newer paint systems their ain't no way I'm gonna use ospho. If you start with clean rust free metal and a good quality primer I don't see a need for it on a car. Theirs a big difference in a rusty ole buggy and a show car. I used something called oakite on my 74 bronco 13yrs ago and haven't seen any problems, but I was younger and didn't know any better. I had been using epoxy for years but glad I found spi its way better than the other. I always thought we were using ospho right but now that I know better I'm sticking with just epoxy on everything.
 
#5
The only time I ever had a problem was when I first used the stuff on the roof of my Coronet R/T. I failed to rinse it off because like Shine stated the directions for use didn't say to. Skimmed the roof with filler, sanded primed, painted, cleared and then when buffing a little bubble kept appearing. Couldn't figure out why but upon Barry's advice I cut it open and low and behold every layer was stuck to the paint chip, including the filler. All that remained on the car was the black layer of Ospho. Since that time I faithfully reapply the Ospho and while it is wet I scrub with soap and water using a Scotchbrite pad and rinse thoroughly. Never had any issues doing it this way.
 
#6
It's interesting that the message has evolved some. I think quietly most of us who are in the biz knew that if used exactly the right way, acid treatments (especially ones sold by auto paint companies) can work.

But there are too many ways to get it wrong, so I personally will keep steering people away from acids unless they demonstrate a really good understanding of the procedures and risks.
 
#7
Old thead, I know. If I have re-sand blasted something that had ospho on it, should I still neutralize? Re-ospho and then neutralize? I am having trouble with the idea of washing a sand blasted surface with water.
 

Barry

Paint Fanatic
Staff member
#8
Old thead, I know. If I have re-sand blasted something that had ospho on it, should I still neutralize? Re-ospho and then neutralize? I am having trouble with the idea of washing a sand blasted surface with water.
NO, sandblasting takes care of everything.
Guess how your new e-coated parts are done? Dipped in a water and phosphoric acid solution 50-60% then dipped in a pure water tank.
 
#9
Thanks Barry. I'll leave the re-blasted surfaces alone then. What I did was blast about 50% of the bottom checking for any suspect areas that needed patch work. I ospho'd after that, and I didn't rinse it off. (Wasn't on the SPI forum then). Now my patching is done and I'm doing round 2 of blasting. Good news is that I havent touched the top (body colored) panels yet, so no acid risks on any surfaces that would get buffed.
 
#10
My grandfather used ospho on every piece of metal on every horse carriage he restored and I don't know of any problems he ever had. But that was oil base enamel and mostly synthetic enamel. We never washed it off with anything but mineral spirits. We took everything to bare metal ospho, primer, filler, primer then paint.Now on a car and newer paint systems their ain't no way I'm gonna use ospho. If you start with clean rust free metal and a good quality primer I don't see a need for it on a car. Theirs a big difference in a rusty ole buggy and a show car. I used something called oakite on my 74 bronco 13yrs ago and haven't seen any problems, but I was younger and didn't know any better. I had been using epoxy for years but glad I found spi its way better than the other. I always thought we were using ospho right but now that I know better I'm sticking with just epoxy on everything.
 
#12
I'm sorry to beat a dead horse.. but just to confirm what I have read, if some one applied ospho (my buddy trying to help with his project) I can leave it for months... when ready, I can neutralize it as described, then sand blast and coat with epoxy and not have adhesion problems?
 
#14
Wow, I hate to throw this in here but... The few times that I used Ospho I found it had a sticky, maybe cheap lacquer or enamel base when not rinsed off. Am I correct? If it's left to dry there is that film, sometimes rubbery even after months. This is why I haven't used it much. Am I missing something? I grew up with dupont and MS etches btw... and had good results with them. Now that acid etches are not as prevalent as they used to be I have found that I really like kbs rustblast, another phosphoric based etch that really works well. Even though the directions on all the above don't specify to dry the metal after rinsing, I have found it better to do so, with a cloth etc...
 

Barry

Paint Fanatic
Staff member
#15
Seems from memory the oshpo is 52-55% acid and rest water??
Not sure where the rubbery film came from?
Always rinse and dry.
 
#16
When the intention is to leave ospho on the panel for protection, it still has to be wiped off with a dry rag, leaving only a thin film.
This would be in the case of protecting the bare metal during the body working process, and when ready for paint then it should be rewet with a scotch pad and rinsed off completely.
 

bing98

New Member
#18
Below is a picture of an area I am going to repair. As you can see there are a lot of nooks and crannies as well as overlapping seams. My plan of attack is as follows:
  1. Sand blast as much of the area that I can
  2. I'm going to remove the damaged portion of the rail.
  3. Treat the whole area with Ospho including inside the rail and behind the trailing arm mount. The mount is the piece with the three bolt holes that form a triangle. As I can't really blast behind the mount I thought I would bend one side down to gain access and then apply liberal amount of Ospho. The idea is to treat any remaining rust in the pitted areas and hope it seeps into the overlapping seams.
  4. Once the rail is repaired I plan to re-activate the Ospho and wipe it down per Barry's instructions to neutralize it. My only concern is that DAing large portions of the area with 80 is not possible. Will a thorough rinse/wipe down be sufficient?
IMG_4026.JPG
 
#19
That frame rail can be drilled and removed, they probably make a replacement that can be sectioned and replaced, is this what you were planning? The other mount looks like the same situation. The spot welds can be drilled and the piece actually replaced with new. While the bits are off, you can address the inaccessible areas. Careful with sandblasting as many times you can't get all the sand out of blind channels, it gets wet and you have accelerated rust there. Personally, in blind areas where there is no other practical choice I would use silver MCU.
 
#20
Thanks for the input. I spent Saturday sand blasting. I wanted to see how bad things were after it was cleaned up. To my surprise the whole thing is very solid with the exception of the side of the rail. Normally there is a reinforcement that covers the whole area. As you can see it is tacked to the side and bottom of the rail. Water in between what caused the rail to rot, but luckily it's only the area you see on the side. The bottom is super solid. I have a new reinforcement from GM so once I get the rail repaired and the area primed I will weld it in.

The inside of the mount couldn't be accessed for blasting and its outside lip is sandwiched between the floor pan and inner rocker. The area looked clean and super solid even before blasting so I didn't want to disturb. After blasting I treated the inside of the mount with Ospho(twice). It will be a few weeks of panel fabrication in other areas before I can get to priming so the Ospho will protect it from flash rust.

The plan is to re-activate the Ospho with more Opsho, scrub with red scotchbrite, rinse with a spray bottle of water and wipe to remove the acid film before W&G remover and primer. I have a refrigerated air drier on my compressor so I will blow dry everything with nice dry air one section at a time. Does this sound like a solid plan of attack???

I have the big sections like rocker and inner reinforcement but still lots of pieces to fab.
IMG_4044.JPG

Made my first template last night...
IMG_4052.JPG
 
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