http://www.crankshaftcoalition.com/wiki/Rust_encapsulatorsFiftyfifty took his thread in a different direction.
In answer to the original post, many people extolled the virtues of epoxy primer over clean, rust-free, blasted metal. They are correct - epoxy primers create a water barrier against exterior water reaching the metal surface.
jomichael is right about epoxy being of limited usefulness when applied over rusted metal. And, "rust encapsulators" are of limited use when applied over clean, rust-free metal (and/but, loose rust should first be removed.
Most (all?) of the "rust encapsulators" use water as their "hardening catalyst" - water and water vapor above and below the layer of paint help to harden the paint. The resultant paint surface is impervious to water transfer.
After curing, epoxy paint and water-hardening rust-encapsulator paints need different special preparations when applying over-coats of any paints. The overcoat paint company might have specific instructions/warnings for use with either type of undercoat.
