Neutralizing Ospho on pitted abrasive blasted Steel.

Thomas Luba

New Member
63 Falcon Sprint - Prep for SPI epoxy.

After I had my car dipped there were a number of the areas on the undercarriage and inside on the floors that were questionable, particularly around spot welded seams. I then proceeded with abrasive blasting most of the underside and floors thinking it would clean up things nicely and save time sanding. About 4 days later there was a considerable amount of rust showing up everywhere.

Before metal treating the body to prove my process I first tried treating a door with Ospho then washed while still wet using a brush, Dawn soap and rinsing with a garden hose and warm softened water and drying with an electric leaf blower. It didn't just flash or haze a bit with rust. I would describe it as bloom. There was such a ridiculous amount of rust I wound up sandblasting again.

So now I am spot treating with Ospho on the chassis and wiping with a wet cotton rag while still wet repeatedly ringing out and soaking the rag. I first dry with a clean cloth and then with a hair dryer. There is still some rusty haze. Nothing like before but no matter how well I rinse the blasted pitted steel still dries with a chalky film. Areas that are smooth have an uneven amber and blue tint similar to steel that has been heated. Not chalky. It seems the rough surface is inhibiting a complete rinse. Additionally it is difficult to rinse the welded seams as there is always some seepage after rinsing.

I have already tried sanding the rust instead of using metal treatment but there are so many nooks and crannies that I just can't completely remove all of the rust.

I'd like to hear from some of the pros regarding this and how to proceed.

I'd like to add that the chalky appearance I observed is minimal.
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Active Member
That chalky film and amber blue colors is Ospho residue. Using a wet rag and ringing it out is redepositing acid residue back on the surface. The only way to remove it is a strong stream of water. The rust you see after rinsing is probably iron in the water. From what I have been told it is harmless. If you are worried about the "flash" rust, spray 2 coats of epoxy in a small area, wait 2 days, then 80# da that area back to metal. I think you will be amazed at what the metal looks like.