Cast Iron Stairs - Rust Proofing?

[Anonymous]

We just had our exterior cast iron stairs refurbished about 6 months ago, but they appear to be rusting in some spots. I don't know if this is a normal thing to experience or if the paint job was done improperly. There is no rusting at the joints per se, just a layer of rust appearing under the doormat, and planters. Can you recommend a sealer or spray that will keep this from spreading?

[Anonymous]

Moisture persisting under the door mat and planter may be the culprit in rust formation here..

Was a primer used on the cast iron steps like Zinsser Bulls Eye, followed by a Rust Oleum product or like kind? I'd be calling the painter on this.