Rust spots come through the paint. Preventable with proper surface preparation and priming.
RUST STAINS PROBABLE CAUSES
Improper surface preparation. Use of nails not protected against rusting. Failure to countersink and apply rust-inhibitive primer. Painting over rusty nailheads, in a short time the rust will bleed through again.
Countersink the nails, spot prime and use acrylic caulk. Rust spots will reappear if you repaint over the rusty spots caused by nails or other rusting metals without prescribed preventative measures. Specify galvanized, aluminum or stainless steel nails.
PRIMERS & EXTERIOR FINISHES
Priming and proper surface preparation are essential with a corrosion resistant primer. Select a top quality exterior paint in the color and sheen of your choice.