POR-15 is a long standing rust treatment that I should get paid to support - but I don't! I have to pay the same (exorbitant!) prices of $75/Qt. everyone does. I say this because, over many years since first finding and using POR-15 (Paint Over Rust) system, as well as it's Metal Prep rust conversion preparation, I've tested it, seen it perform over several years in the field and used it in some very tough conditions.
The tailgate for this 1956 International Harvester was in great overall shape, albeit with a skiff of surface rust across most of its surface. Like the rest of the truck I sprayed a few heavy coats of Metal Ready and left it over night for the Phosphate to do its job.
After 1 days the phosphate dries to a whitish powder, turning rust (Iron Oxide)
to an inert substance (Iron Oxite).
Still a little rust left after the first treatment, so a second is often needed:
A couple of holes that someone made for the licence plate had to be filled. Metal Ready is also supposed to make metal more conducive to welding, so I thought it a good time to get it done.
With a copper plate on one side I welded up the holes, then ground them down flush:
After a little work with the grinder, the holes were gone.
Next up some primer, a good sanding and it's off to paint.