White rust is a white powdery corrosion product that appears on the surface of galvanized warehouse cages; it looks like mold, but is actually zinc oxide formed as the zinc layer oxidizes in damp, poorly ventilated conditions. Fresh cages just out of the factory are especially prone to white rust, often caused by moisture trapped during sea freight or warehouse storage.
White rust and red rust are different: white rust occurs on the zinc layer surface—light cases wipe off and do not affect the base metal; red rust is the actual steel rusting after the zinc layer has corroded all the way through—that is true corrosion. If you find white rust, don't panic: assess how much zinc is left before deciding how to treat it.
Three preventive measures: first, once new cages arrive, unwrap them and air them out—don't leave them sealed in woven bags. Second, keep the warehouse dry, holding relative humidity below 60%, and leave ventilation gaps between cages. Third, for export or long-distance transport, ask the manufacturer to passivate the coating or apply anti-rust paper.
How to treat existing white rust: for light cases, wipe off the white powder with a dry wire brush or non-woven cloth, expose the silver-gray zinc layer, then spray a coat of clear lacquer or anti-rust oil for protection. For severe white rust (large areas of blackened, peeling zinc layer), grind and re-spray zinc-rich paint—never just paint over it, or corrosion continues underneath.
On acceptance, new cage surfaces should be smooth, uniform and free of white spots. All galvanized cages shipped by Nanjing Tongnuo Warehouse Equipment Manufacturing Co., Ltd. receive passivation sealing, and we remind customers to unwrap and air them promptly on arrival.