Ospho and epoxy primers

SDE

Well-known Member
I just looked at a Bulletin from the Skyco Co. that stated that a good quality oil based primer will give good results and that you should do a trial test if using epoxy primers. It looks to me like the oil based primer is the recommended primer to be used. So which primer would you use? Also I am using Iron Guard IH red for the topcoat.
TY
SDE
 
(quoted from post at 10:44:11 10/04/19) I just looked at a Bulletin from the Skyco Co. that stated that a good quality oil based primer will give good results and that you should do a trial test if using epoxy primers. It looks to me like the oil based primer is the recommended primer to be used. So which primer would you use? Also I am using Iron Guard IH red for the topcoat.
TY
SDE

Epoxy primer is IMO the best you can do with primer and is compatible with basically any topcoat or surfacer you would ever get your hands on.

This of course comes with the caveat that they tend to be more finicky to work with. This seems to be a general rule of thumb: the better the product, the more precise your prep work has to be to get what you want (could be an expectations placebo, admittedly). Epoxy needs a CLEAN surface whereas cheap rustoleum seems to just mix with whatever oil residue is on the surface rather than run away from it and create fisheyes.

Some epoxies (SPI and HOK among them) are extra finicky about acid products being used under them and any acid left on the surface will cause issues with adhesion. Others play nicer with acid residue (Kirker/Summit) but it would still be in your best interest to make sure it is all removed and/or avoid it if possible under ANY primer.

Others on the site will speak of acid treatments as though they are a necessary step. They are not, if you sand blast adequately and get the surface sealed down with epoxy, you won't have any issues. People have been restoring cars and tractors like this for years. Save the acid for where it is absolutely needed.
 
Amen! I just visted the SPoly site today to refresh my memory on Ospho (or other acid products) prep and handling. One of the reasons I prefer Kirker.
 
Yakob..I agree 100% with your info. I've been in this business for a living since 1971. (collision repair,restorations etc) My opinion, get rid of the rust or don't bother doig the job. NOTHING is going to forever neutralize your rust and rust pits. Blast the rust or castings clean and get immediatly back on with 2 part epoxy..best you can do. Then do all surface work and filler work and wherever you go to bare metal, epoxy again before final surfacer and blocking. The market is full of snake oil short-cuts. Everyone go to a well known new car dealership body shop and see what they use and get their opinions. Even a good reputable private owned shop. Wire brushing and using snake oil doesn't cut it..at least for long.
 

I am one of those who feels very strongly about acid treatment ever since the paint guy at the local jobber told me that I had to use it and I researched it. Many or perhaps even most auto-body shops don't worry about it because their customers simply want their collision damage repaired and they will have traded the car long before the rust that is trapped underneath can eat enough steel to cause the paint to bubble. I put too much work into prepping my projects to leave the rust in there. Anybody who thinks that sandblasting is going to get all of the rust out of the pits and just say that it is the best that they can do and ignoring all that black that is still there is just kidding themselves and taking a major short cut. There are two ways to get rust out of pits and seams and deep scratches. Either cut them all out and butt weld new metal in or use a phosphoric acid rust converter. I have talked to plenty of guys who do restoration work and they all use rust converter. A favorite is Rust Mort by SEM the auto body shop supplier. When used according to instructions it doesn't leave acid behind like some people insist happens. What is left behind is iron phosphate, the same coating that is on your impact wrench sockets. I have been unable to find any caution about priming over iron phosphate. Many restoration shops will not do a frame off resto without taking the body and getting it completely dipped in a phosphoric acid bath followed by proper and adequate rinsing and neutralizing so that they are not trying to prime over acid. On the antique car that I recently finished there was many feet of lapped over spot welded seams. I didn't just ignore the rust that I knew was inside those seams like most auto body shops would. I went over it closely and dug out any old seam sealer that was loose. I then injected Rust Mort with a syringe then followed with a water rinse which I then followed with an alcohol rinse. I refuse to prime over rust or acid. Admittedly all of this extra work would put high quality shop work out of the reach of many people considering a restoration, but the guy who is doing it himself and wants his project to outlast him and takes pride in his work won't take the short cuts.
 
"Many restoration shops will not do a frame off resto without taking the body and getting it completely dipped in a phosphoric acid bath followed by proper and adequate rinsing and neutralizing so that they are not trying to prime over acid."

How do they neutralize the acid?

Thank you everyone for your replies.
 
(quoted from post at 05:54:46 10/05/19) "Many restoration shops will not do a frame off resto without taking the body and getting it completely dipped in a phosphoric acid bath followed by proper and adequate rinsing and neutralizing so that they are not trying to prime over acid."

How do they neutralize the acid?

Thank you everyone for your replies.

SDE, it is very simple technology. A dip in a slightly alkaline solution neutralizes the rinse tank back from alkaline to neutral, so the acid on the metal is gone.
 
(reply to post at 08:54:46 10/05/19)
I am repainting a 40 year old Ford.. I used electrolysis starting with the calcium filled wheels to get a feel for pre-paint and paint processes starting with the least sensitive parts. I've worked in and around auto manufacturing including paint. We used to dip entire bodies in phos acid so I experimented with processes. Electro with PH Up and Lye did a fine job removing paint and rust of all progressions except a few spots of very stubborn paint that I ground off or feathered. High pressure water spray finished the job to bare metal. Spray with 100% phos was not a conclusive improvement and saw some flash rust which I removed with more phos, then rinse and dry with a clean cloth and light heat with a propane weed burner. A phos dip will not pickle some metals to where they will be rust proof until prime. The hubs seem better the sheet steel in this regards to steel grades, metal forming method and previous treatment may be a factor. Some metal was more prone to rust bloom. These were experements in chemistry to be successful in the more visible and challenging hood and front fascia. CONCLUSION: You have to get the metal dried quickly and a quick shot of primer. Electrolysis alone seems to de-paint, de-rust, de-grease metal parts with low risk and great efficiency.
 
I am repainting a 40 year old Ford.. I used electrolysis starting with the calcium filled wheels to get a feel for pre-paint and paint processes starting with the least sensitive parts. I've worked in and around auto manufacturing including paint. We used to dip entire bodies in phos acid so I experimented with processes. Electro with PH Up and Lye did a fine job removing paint and rust of all progressions except a few spots of very stubborn paint that I ground off or feathered. High pressure water spray finished the job to bare metal. Spray with 100% phos was not a conclusive improvement and saw some flash rust which I removed with more phos, then rinse and dry with a clean cloth and light heat with a propane weed burner. A phos dip will not pickle some metals to where they will be rust proof until prime. The hubs seem better the sheet steel in this regards to steel grades, metal forming method and previous treatment may be a factor. Some metal was more prone to rust bloom. These were experements in chemistry to be successful in the more visible and challenging hood and front fascia. CONCLUSION: You have to get the metal dried quickly and a quick shot of primer. Electrolysis alone seems to de-paint, de-rust, de-grease metal parts with low risk and great efficiency.[/quote]

Faust, I have seen very little flash rust. When I have had it I just hit it again with the acid, then rinsed with water followed by a cloth drenched with alcohol. Quick dry no rust.
 
(quoted from post at 06:35:52 10/05/19)
I am one of those who feels very strongly about acid treatment ever since the paint guy at the local jobber told me that I had to use it and I researched it. Many or perhaps even most auto-body shops don't worry about it because their customers simply want their collision damage repaired and they will have traded the car long before the rust that is trapped underneath can eat enough steel to cause the paint to bubble. I put too much work into prepping my projects to leave the rust in there. Anybody who thinks that sandblasting is going to get all of the rust out of the pits and just say that it is the best that they can do and ignoring all that black that is still there is just kidding themselves and taking a major short cut. There are two ways to get rust out of pits and seams and deep scratches. Either cut them all out and butt weld new metal in or use a phosphoric acid rust converter. I have talked to plenty of guys who do restoration work and they all use rust converter. A favorite is Rust Mort by SEM the auto body shop supplier. When used according to instructions it doesn't leave acid behind like some people insist happens. What is left behind is iron phosphate, the same coating that is on your impact wrench sockets. I have been unable to find any caution about priming over iron phosphate. Many restoration shops will not do a frame off resto without taking the body and getting it completely dipped in a phosphoric acid bath followed by proper and adequate rinsing and neutralizing so that they are not trying to prime over acid. On the antique car that I recently finished there was many feet of lapped over spot welded seams. I didn't just ignore the rust that I knew was inside those seams like most auto body shops would. I went over it closely and dug out any old seam sealer that was loose. I then injected Rust Mort with a syringe then followed with a water rinse which I then followed with an alcohol rinse. I refuse to prime over rust or acid. Admittedly all of this extra work would put high quality shop work out of the reach of many people considering a restoration, but the guy who is doing it himself and wants his project to outlast him and takes pride in his work won't take the short cuts.

The black iron phosphate coating, when using this product, only exists in places where the rust was, correct? It does not leave the entire area converted to iron phosphate.
 
(quoted from post at 08:59:41 10/07/19)
(quoted from post at 06:35:52 10/05/19)
I am one of those who feels very strongly about acid treatment ever since the paint guy at the local jobber told me that I had to use it and I researched it. Many or perhaps even most auto-body shops don't worry about it because their customers simply want their collision damage repaired and they will have traded the car long before the rust that is trapped underneath can eat enough steel to cause the paint to bubble. I put too much work into prepping my projects to leave the rust in there. Anybody who thinks that sandblasting is going to get all of the rust out of the pits and just say that it is the best that they can do and ignoring all that black that is still there is just kidding themselves and taking a major short cut. There are two ways to get rust out of pits and seams and deep scratches. Either cut them all out and butt weld new metal in or use a phosphoric acid rust converter. I have talked to plenty of guys who do restoration work and they all use rust converter. A favorite is Rust Mort by SEM the auto body shop supplier. When used according to instructions it doesn't leave acid behind like some people insist happens. What is left behind is iron phosphate, the same coating that is on your impact wrench sockets. I have been unable to find any caution about priming over iron phosphate. Many restoration shops will not do a frame off resto without taking the body and getting it completely dipped in a phosphoric acid bath followed by proper and adequate rinsing and neutralizing so that they are not trying to prime over acid. On the antique car that I recently finished there was many feet of lapped over spot welded seams. I didn't just ignore the rust that I knew was inside those seams like most auto body shops would. I went over it closely and dug out any old seam sealer that was loose. I then injected Rust Mort with a syringe then followed with a water rinse which I then followed with an alcohol rinse. I refuse to prime over rust or acid. Admittedly all of this extra work would put high quality shop work out of the reach of many people considering a restoration, but the guy who is doing it himself and wants his project to outlast him and takes pride in his work won't take the short cuts.

The black iron phosphate coating, when using this product, only exists in places where the rust was, correct? It does not leave the entire area converted to iron phosphate.

Yes true, Yakob. Rust becomes a protective coating.
 
(quoted from post at 11:18:49 10/07/19)
(quoted from post at 08:59:41 10/07/19)
(quoted from post at 06:35:52 10/05/19)
I am one of those who feels very strongly about acid treatment ever since the paint guy at the local jobber told me that I had to use it and I researched it. Many or perhaps even most auto-body shops don't worry about it because their customers simply want their collision damage repaired and they will have traded the car long before the rust that is trapped underneath can eat enough steel to cause the paint to bubble. I put too much work into prepping my projects to leave the rust in there. Anybody who thinks that sandblasting is going to get all of the rust out of the pits and just say that it is the best that they can do and ignoring all that black that is still there is just kidding themselves and taking a major short cut. There are two ways to get rust out of pits and seams and deep scratches. Either cut them all out and butt weld new metal in or use a phosphoric acid rust converter. I have talked to plenty of guys who do restoration work and they all use rust converter. A favorite is Rust Mort by SEM the auto body shop supplier. When used according to instructions it doesn't leave acid behind like some people insist happens. What is left behind is iron phosphate, the same coating that is on your impact wrench sockets. I have been unable to find any caution about priming over iron phosphate. Many restoration shops will not do a frame off resto without taking the body and getting it completely dipped in a phosphoric acid bath followed by proper and adequate rinsing and neutralizing so that they are not trying to prime over acid. On the antique car that I recently finished there was many feet of lapped over spot welded seams. I didn't just ignore the rust that I knew was inside those seams like most auto body shops would. I went over it closely and dug out any old seam sealer that was loose. I then injected Rust Mort with a syringe then followed with a water rinse which I then followed with an alcohol rinse. I refuse to prime over rust or acid. Admittedly all of this extra work would put high quality shop work out of the reach of many people considering a restoration, but the guy who is doing it himself and wants his project to outlast him and takes pride in his work won't take the short cuts.

The black iron phosphate coating, when using this product, only exists in places where the rust was, correct? It does not leave the entire area converted to iron phosphate.

Yes true, Yakob. Rust becomes a protective coating.

Thanks for clarifying. That has been my experience in using this type of product and I didn't want someone going away thinking that just phosphoric acid would leave a protective coating on bare steel. I use them as an etching when I cannot sand blast and sanding is not feasible.

A lot of these different coatings promise a lot of "brush on, let dry, prime" in the instructions. These are the ones that are of more concern. Looks like Rust Mort is more specific than this. One thing to pay attention to is their call out of "making sure the iron phosphate coating is not hiding more rust" which in reality...implies that you to continue removing the coating/rust until you are at bare steel.

Ospho, on the other hand, outlines a lot of different processes that I'd call simpler than reality and are begging someone to have a bad day with unreacted acid. I like to quote label directions but with all these products, things get hairy doing so. there are too many fly-by-night companies making this type of product.

I also don't want people to go away thinking that these products, or any other processes are a replacement for sand blasting. That is the single best preparation step, in my opinion.
 
Faust, I have seen very little flash rust. When I have had it I just hit it again with the acid, then rinsed with water followed by a cloth drenched with alcohol. Quick dry no rust.[/quote]

I dropped the tool box back in for a full dip, then dried it quickly. For what it's worth, I used to work in a truck factory a few decades ago, and before paint we had a body flush to remove gloves, cigarette buts, trash (yeah I know), then a dip into "the green pool" and off to paint. The line speed was one per 55 seconds so I'm sure it was a full strength solution, however that was virgin metal. The tool box pickled ok, the fenders a little better and the hubs went dark grey. I think the metallurgy has something to do with the reaction. Now I'm going to be trying to clean up the fthreaded asteners/nuts.
 

Yakob,

My use of Rust converters goes back close to 40 years. The first that I used was an aerosol sold by one of the biggest name brands. It appeared to contain latex. I was initially impressed but then found that if not top coated it tended to lift and trap moisture. Sixteen years ago as I have already stated, I found out about acid wash prior to priming. At nearly the same time I had some tractor wheels sandblasted at a big shop. When I went to pick them up there was a lot of black still on them here and there. They touched them up for me. I didn't chemically analyze the black but I am confident that it was rust. Another experience that I had was when a hay customer who operated an autobody shop took some panels from a tractor and painted them as a favor. Two years later there were bubbles in the paint where some rust pits had been. I don't want rust under my paint. This led me to the SEM product, which as I have stated, is watery thin so it penetrates. I follow the instructions, keeping the surface wet and agitating it periodically for 15 minutes. I then rinse aggressively to remove any non-converted acid so that I am not priming over acid. A friend used Ospho on a project. I was suspicious of it. This product left an all-over black coating which looks good but I doubted the longevity of it. I saw his project recently and it was not looking good. My experience and observation tells me that one needs to be aware of the chemistry and follow instructions. Perhaps the type of coating that you are so against is the type that my friend used.
 
(quoted from post at 06:00:23 10/09/19)
Yakob,

My use of Rust converters goes back close to 40 years. The first that I used was an aerosol sold by one of the biggest name brands. It appeared to contain latex. I was initially impressed but then found that if not top coated it tended to lift and trap moisture. Sixteen years ago as I have already stated, I found out about acid wash prior to priming. At nearly the same time I had some tractor wheels sandblasted at a big shop. When I went to pick them up there was a lot of black still on them here and there. They touched them up for me. I didn't chemically analyze the black but I am confident that it was rust. Another experience that I had was when a hay customer who operated an autobody shop took some panels from a tractor and painted them as a favor. Two years later there were bubbles in the paint where some rust pits had been. I don't want rust under my paint. This led me to the SEM product, which as I have stated, is watery thin so it penetrates. I follow the instructions, keeping the surface wet and agitating it periodically for 15 minutes. I then rinse aggressively to remove any non-converted acid so that I am not priming over acid. A friend used Ospho on a project. I was suspicious of it. This product left an all-over black coating which looks good but I doubted the longevity of it. I saw his project recently and it was not looking good. My experience and observation tells me that one needs to be aware of the chemistry and follow instructions. Perhaps the type of coating that you are so against is the type that my friend used.

I perceive your mention of acids as a must have, whereas this is not always the case. I talk of sand-blasting as it is a must have, but there are other more labor intensive ways to prep. To make this more clear and find common ground -- I believe sand blasting is the best, most effective overall prep work but may leave rust in places that can sometimes be best dealt with by properly using an acid product.

The original post was in regard to what type of primer to use over the acid product.

Let's study the TDS from Rust-Mort more closely:

"BLACK COATING:
A black coating indicates that there was a sufficient amount of Rust Mort applied to the panel to convert but not
remove the rust completely. This usually happens when the user stops the removal process before completion. This
black, insoluble coating is suitable for further top coats as long as there is no rust present underneath."

This piece of instructions can be misleading. How do you know there is "no rust present underneath"? Easy! -- you scuff the existing phosphate to reveal either bare metal or more rust. Hence, what this product is *really* telling you is that it is intended to be used to remove, not convert, but this paragraph may lead people to improper usage where they are actually hiding rust. Neither of us want that, and it is a "per the instructions" quote. Yes, Rust Mort converts the rust, but NO, it does not do it in a way that is actually leaving a phosphate suitable for topcoating and they allude to that in their own tricky wording. Rust Mort should be used to remove all traces of rust, completely. I think you agree with this based on how you have outlined your own use.

OSPHO:

Studying the Ospho instructions will show you various different instructions, open to some interpretation (i.e. "heavy" rust -> Merriam Webster doesn't define this). Some of these instructions look really good to a rookie user as they promise a wipe on, conversion coating that can be topcoated. NO WAY will this leave you happy. Again, I think you agree with this based off of your last statement; Using it this way 1. leaves rust underneath the so-called phosphate coating or 2. leaves acid residue and wrecks adhesion. This is why Ospho also says to "test when using an epoxy primer" over their product. They are trying to cover their A$$ while still making things look super easy.

I am not against these products, I am against people being led to think they *have to* use them. I'm also against the misleading instructions of the labels. There are dozens of products out there that boil down to different %'s of phosphoric acid being peddled with different promises but in reality need to be used the same to dissolve rust away and leave bare steel.

I use the "prep and etch" one from Home Depot as it is about the cheapest and easily most readily available phosphoric product I can get my hands on. I've also used Naval Jelly (which HD also carries) but I don't like it and it is wildly overpriced for the amount you get. In reality, Ospho and Rust Mort are extremely overpriced as well. Sure, Rust Mort should have a higher acid concentration. Comparing 35-45% of the Kleanstrip product vs 40-60% of the SEM product doesn't show me a logical pricing of 10x.

In any case: Phosphoric acid = Rust REMOVAL. With any one of these given products, you need to follow generic phosphoric acid instructions that tell you to remove rust completely and rinse/neutralize the product while still wet, leaving a perfectly clean piece of bare steel. Following the label instructions on these products will leave you disappointed in certain cases and this is what your friend did with Ospho.
______________________________________________

Things like paintron were talking about were a TRUE conversion coating that created a phosphate coating on bare steel (i.e. "parkerizing" solutions). These leave a true conversion coating not just "a layer of converted rust on top of other rust." The problems with these are:
1. price
2. availability
3. even more complex usage
4. lack of necessity

I think you agree on these points as well, since you aren't using these parkerizing products, you obviously don't think that we need a full on phosphate coated substrate on our tractors.
______________________________________________

I don't doubt you had the experience with the pieces your hay guy did for you. I don't doubt that your new process has avoided this type of issue. My instinct and experience tells me that those pieces had numerous shortcomings in prep work. I do not want people to think that they need to prep every square inch of something with acid.
 

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