Treating Rust on Wrought Iron Before Painting

Wrought iron gate with worn paint and surface rust on the bars

Twenty minutes of brushing now saves two hours of grinding later, as long as the rust is the surface kind. The recoat interval that austin wrought iron gates backyard beans and grains uses is shorter than most rust converter labels suggest, because a gate in Austin, TX stands in humid air for much of the spring. Wrought iron, cast iron and mild steel all rust, but they rust differently, and the treatment follows the damage.

Surface rust, pitting and scale

Close view of decorative wrought iron bars on a gate

Surface rust is orange powder that wipes off and leaves smooth metal underneath. Pitting leaves small craters that hold moisture, and scale is the thick, layered flake that lifts in sheets. Run a fingernail across the bar. If it catches in dents, the metal has lost thickness. If flakes come away in layers, the scale has to come off completely before anything else happens.

Where a rust converter works

Iron gate bars photographed in black and white

A converter turns light rust into a stable black layer that primer can grip. It does that job well on surface rust inside a scroll or under a collar, where a wire wheel cannot reach. It does not work on heavy scale, and it does not fill pits. Brushed over loose flake, it simply glues the flake in place and the new coat peels with it.

When the metal must be ground back

Scale, deep pitting and any rust that has swollen a joint gets ground or wire-wheeled to bright steel, or to the dull gray of clean wrought iron. Grind with the grain of the bar and stop before the surface is thinned. A weld bead from a past repair often rusts at its edges first, so that line gets a second look with a file.

Humid spring weather near the water

Gates close to Lady Bird Lake and the Colorado River sit in damp air most mornings from March through May, and iron left bare overnight there picks up a rust film by sunrise. A gate in Clarksville or Bouldin Creek, with trees overhead and little breeze, stays wet longer than one on open ground. Work late morning to early afternoon, when the metal is dry, and prime within the same day.

What goes on after the treatment

A rust-inhibiting primer goes on over clean, dry metal, and the first coat is brushed rather than sprayed so it works into the seams. Enamel paint follows once the primer has cured as the label directs. Treat the underside of the bottom rail too, since splash from the ground keeps it wet and it rusts first.