jimdog

Member
I'm restoring my Farmall 826 and have a question on using OSPHO on sheet metal.The paint store told me to use the E-Poxy primer on bare metal.Will I have a problem using it over the OSPHO? OSPHO is basically phosphoric acid.
Thanks for any advice.
 
It depends on the epoxy primer. I have use Omni epoxy primer over phosphoric acid with no problems but I did extra prep. After the initial acid cleaning I wiped all of the metal down with a diluted phosphoric acid. Something like 5 to 1 water to acid. I wiped it dry and tried to remove any trace of white acid residue. I then scrubbed the dry metal with a scotch bright pad. Then a good solid wipe down with wax a grease remover. Then shot the primer. I don't think you want to leave a heavy acid residue for good primer bonding to metal. Some epoxy primers do not work with phosphoric acid so ask your paint guy and double check.
 

When I was picking up paint for my dump truck body, the paint guy asked me if I had acid wash. I had never heard of it. He told me that I needed to use it or there would be rust still there that would cause the new paint to lift soon. I use a different brand, but I give it a good rinse after it has had time to work in order to remove any residue. Never try to paint over any residue. I put small pieces in a bucket and use my pressure washer on large panels. I have never had any problem with flash rust but if the air is humid I will follow the water rinse with an alcohol wipe. You may have clean metal but most old tractors have rust pits which even after sandblasting will hide tiny rust spots.
 
I know of one epoxy brand, Southern Polyurethane, that is not to be used over acid treatments as it contains acid. It is best to check with the epoxy maker for their specific recommendation. OTOH, I've used Kirker over acid. Really, it depends on the epoxy
 
You can use epoxy primer after treating it with OSPHO. The metal will need to be rinsed and dried first. Unless the metal had a lot of rust on it I don't think the OSPHO will help you much.
 
I am no expert but when I did bare metal I used a acid etching primer or the metal and worked fine. did one truck and one tractor that way.
 

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