Flash Rust

danp76

danp76

Oldtimer
I have a rebuilt engine that was hot tanked and been on an engine stand in my shop for a few years. The engine has developed some flash rust. I scrubbed it with SEM Rust Mort, followed by a thorough rinse. I then washed the engine with Dawn and a red scotch pad and thoroughly rinsed it again. The engine has a mild coating of flash rust, what do you guys use to seal or get rid of this? I was told OSPHO, but I believe OSHO must be water rinsed to neutralize, which would create additional flash rust? thanks guys.
 
Dan, the Ospho does need to be water washed well. It will effect the adhesion if it is not removed and neutralized..

That does not mean you can not use it to get ris of the flash rust. Just make sure you rinse it well.

John
 
Hi John, upon rinsing the Ospho, I will reintroduce flash rush as a result of the water rinse....that's my concern.
 
Ospho is phosphoric acid and shouldn't be used on cast iron. Use evaporust, it works the same way, but doesn't contain any acid. It will flash rust though, you just don't have to rinse so thoroghly. That is, its easier to get it off.
 
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I don't like it either but it will show up almost instantly in my climate. If you wash it and paint it the same day, the flash rust will not be a problem. It may have an orange rusty cast but contains no real significant rust. Wipe it down with W/G remover 30-40 minutes before you shoot it. Use a Scotch Brite pad if you choose to.

Using any acid on cast iron is probably not the best plan but I suspect the caustic wash at the machine shops also contain an acid base but I have to admit, I'm not sure about that. Rust Mort is also phosphoric acid. Since it has already been scrubbed in phosphoric acid, I suspect the Ospho will not be any worse. It certainly does need to be neutralized though.

John
 
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I have found that the 700 with a red scotchbrite removes minor surface or flash rust really well. Spray it down wet, rub it with the scotchbrite, rewet it and wipe it dry. Worth a try.
 
you can not prevent flash rust on cast iron , it just shows it's clean . it will be no problem under epoxy. scuff it with red scotchbrite clean with solvent cleaner and epoxy.
 
shine said:
you can not prevent flash rust on cast iron , it just shows it's clean . it will be no problem under epoxy. scuff it with red scotchbrite clean with solvent cleaner and epoxy.
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This is what I’m dealing with
 

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John Long said:
I don't like it either but it will show up almost instantly in my climate. If you wash it and paint it the same day, the flash rust will not be a problem. It may have an orange rusty cast but contains no real significant rust. Wipe it down with W/G remover 30-40 minutes before you shoot it. Use a Scotch Brite pad if you choose to.

Using any acid on cast iron is probably not the best plan but I suspect the caustic wash at the machine shops also contain an acid base but I have to admit, I'm not sure about that. Rust Mort is also phosphoric acid. Since it has already been scrubbed in phosphoric acid, I suspect the Ospho will not be any worse. It certainly does need to be neutralized though.

John
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Well, a caustic wash is actually a base, the acid is the opposite of a base and if mixed together caustic and creates cottage cheese.

My usual process with blocks is muriatic acid in a 55 gallon drum to derust, then phosphate, which are like the chemicals in ospho. Usually makes a really nice blue tint that wont rust for a few days. I dont see any problem with the ospo, you can add some dawn to the water you rinse with to keep the flash rust down until it completely dries, then use the wax and grease remover to remove any dawn residue.
 
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