Galvanizing and powder coat on gates in Austin heat

The tick of a metal gate cooling at dusk after a long afternoon in the sun is the sound of the finish expanding and contracting, and the notes kept through austin iron gates preflight sim treat that daily movement as the main thing a coating in Austin, TX has to survive. A steel gate carries two kinds of protection, zinc and a topcoat, and each fails in its own way.

Hot-dip galvanizing

A galvanized frame is dipped in molten zinc, which bonds to the steel and also coats the inside of tubing. Zinc sacrifices itself before the steel underneath, so a nick does not start rust right away. The limit is size and heat: a long gate leaf can warp in the bath, and welding on galvanized steel burns off the zinc around the joint and throws fumes that need proper extraction. A weld on a galvanized frame needs its zinc rebuilt afterward.

Powder coat

Powder coat is dry polymer sprayed onto grounded metal and baked on. It lays down thicker and harder than most paint, with no runs. Applied over bare steel it is only as good as the surface prep, so blasting and a clean degrease matter more than the color. Applied over galvanized steel it needs a mild etch so it does not peel in sheets, and the oven temperature has to suit the zinc.

What Austin weather does to each

With highs of 90F or more on over 120 days a year, dark colors on a south-facing gate run hot enough to soften a cheap coat and chalk it within a few seasons. Light colors last longer in the same sun. Rain falls through the whole year here, so a chip does not dry out between storms, and moisture sits in the chip and spreads under the film.

Where finishes fail first

Failure starts at weld seams, sharp picket edges, the underside of the bottom rail and any place water can pool, such as the open end of square tubing. A weld left rough holds a thin coat on its peaks and a thick coat in its pits, and the thin parts go first. Drilling a small drain hole at the low end of a hollow rail keeps water from sitting inside.

Zinc primer under a topcoat

A zinc-rich primer under a liquid topcoat is the common answer when a gate cannot go to a powder coating oven. It protects less than a full dip, but it is a real step up from bare steel and rattle-can primer. Every cut face, grind mark and weld should be primed before the topcoat goes on, and the topcoat should be touched up as soon as a scratch shows.