Galvanized Corrosion – Zinc

Safe Use of Galvanized Pallet Rack

Wet Storage Stain is the term commonly given to the white rust which will later turn to a black and finally, a red rust when moisture rests on zinc coating. The white or gray deposit is formed by the accelerated corrosion of the zinc coating when it is stored in damp and poorly ventilated conditions.

Zinc is a very reactive material and will form zinc oxide when mixed with oxygen from the air; this is the thin hard layer that forms the protective film associated with galvanized coatings. The coating needs carbon dioxide to create this layer 2ZnC03.3ZN(OH)2. Once formed, this layer is weather-resistant and minimizes further corrosion.

The problem arises when galvanized parts are deprived of air and exposed to moisture. This causes a different set of chemical changes in the zinc. Droplets of water, when flattened between two surfaces such as items mounted to pallet rack beams, create problematic environments for zinc, which needs exposure to air. The zinc is attacked by the water, and zinc ions constantly leave the coating to be bound by the water; the absence of carbon dioxide accelerates the corrosion. The zinc cannot be converted to zinc hydroxide to form the protective film and corrosion will persist as long as these conditions prevail.

First Stage: Dimples in Signage Surface Create Pockets for Moisture

Pockets of moisture deprive the zinc coating of carbon dioxide which is needed to form its protective “anodized” film. The first reaction is the white rust, which is then accelerated to black rust as the zinc continues to be deprived of air.

Later Stages: Red/Brown Rust

The most advanced step is the red/brown rust that forms after the zinc has been continuously deprived of air.


Stand the product where all surface areas will have:

  • adequate ventilation,
  • chemical free environment,
  • clean surface, free of soils and buildup which prevent air flow, and
  • can use magnetic signage only in dry areas.
First Stages – Galvanized Corrosion
First Stages – Galvanized Corrosion
  Later Stages – Corrosion
Later Stages – Corrosion

System Highlights:

Galvanized Pallet Rack and Cantilever offer many benefits for a long life in outdoor use and freezer applications.

  • Naturally corrosion-resistant

  • Cost-effective due to longer shelf life

  • Zinc is chemically fused with the steel and requires minimal upkeep

  • Long life in coastal areas where pallet rack is used outside

  • Zinc bath ensures pallet rack is coated completely in every corner

Outdoor storage and racking that is subject to the weather and elements needs a special coating. With proper use and maintenance, galvanized racking can last for decades, but zinc needs to oxidize to maintain that life expectancy. Make sure your galvanized pallet racking and cantilever has adequate ventilation and is dry behind any signage that is applied.

For photos of Pallet Rack and Installations, visit the UNARCO Pallet Rack Photo Library.

Galvanized Wet Stain Correction Methods for Rack

  • Remove items which have trapped in moisture and let zinc “breathe”
  • If there is sufficient zinc coating remaining, scrape existing white rust with a stiff bristle brush (not wire) and expose it to the air
  • If red/brown rust has formed, remove deposits with a stiff bristle brush (not wire) and recoat any surfaces which have no zinc remaining
  • See ASTM – A780 ("Standard Practice for Repair of Damaged and Uncoated Areas of Hot-Dip Galvanized Coatings") for more detailed instructions on repair.

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