Reddish-brown stains and spots on the paint surface.
Non-galvanized iron nails have begun to rust, causing bleed-through to the top coat.
Non-galvanized iron nails have not been countersunk and filled over.
Galvanized nailheads have begun to rust after sanding or excessive weathering.
When painting new exterior construction where non-galvanized nails have been used, it is advisable to first countersink the nailheads, then caulk them with a top quality, waterbased all-acrylic or siliconized acrylic caulk. Each nailhead area should be spot primed, then painted with a quality latex coating. When repainting exteriors where nailhead rusting has occurred, wash off rust stains, sand the nailheads, then follow the same surface preparation procedures as for new construction.