Galvanizing

Galvanizing is the process of coating steel with zinc to stop rust. In the garage door industry, nearly every steel part ships galvanized from the factory. Door skins, track sections, torsion shafts, and hinges all carry a zinc layer. The paint or primer that goes on later sits on top of the zinc, not directly on bare steel.

Zinc protects steel in two ways. First, it forms a physical seal. The zinc layer keeps moisture and oxygen off the steel surface. No moisture plus no oxygen means no rust. Second, zinc acts as a sacrificial anode. If a scratch or cut edge exposes bare steel, the zinc nearby corrodes first. The zinc gives itself up to protect the steel underneath. The steel stays clean until the zinc at that spot is fully gone.

Coating weights:

Galvanized sheet is rated by how much zinc covers it. The unit is ounces per square foot, both sides combined. The most common grades in garage door products are:

• G60: 0.60 oz per sq ft. Used for light interior applications.
• G90: 0.90 oz per sq ft. Standard for door skins and track.
• G115 and above: Used on hardware in salt air or industrial settings.

Most door manufacturers specify G90 steel for panels and track. G90 sheet is the practical standard for a typical residential installation.

A real example:

A 16-foot steel door in a coastal garage is a good case for G90 skins and galvanized torsion springs. Salt air attacks bare steel fast. The G90 coating on the skins adds years of protection. Galvanized springs last longer near the ocean than standard oil-tempered (black) springs. Bottom seals and weatherstripping are rubber or vinyl, so they do not need zinc coating.