The layer of zinc that forms the coating on galvanised metal is under constant attack from corrosion to prevent damage to the underlying steel or aluminium. It is important to maintain the efficacy of the protective zinc layer by keeping the surface clean and removing traces of corrosion as soon as possible. Once the corrosion compromises the zinc layer the oxidisation process corrodes the structural integrity of the metal substrate and causes the unprotected metal to break down.
Inspect the galvanised metal for areas of white surface powdering, which is the sign of zinc corrosion. Look for the presence of orange-coloured corrosion that shows the zinc layer has broken down and the steel or aluminium is rusting.
Apply a water-based degreaser over white powdered areas. Scrub gently with a nylon-bristled brush to remove the white-coloured corrosion from the surface of the zinc. Rinse the galvanised metal in water to remove the corrosion debris and degreaser chemicals.
Spray a phosphoric acid-based galvanised metal cleaner over areas of white powder that remain after completing step 1. Allow the cleaning solution to soak into the corrosion according to the cleaner manufacturer's instructions.
Use a nylon-bristled brush to remove the chemically treated white corrosion. Rinse the metal thoroughly with water to flush away the chemicals and residual corrosion fragments.
Rub orange-coloured corrosion with wire wool to remove surface rust from the metal. Rinse the metal with water to remove the rust particles.
Spray any remaining rust with the galvanised-metal cleaner and allow the solution to soak into the area of corrosion. Use a wire brush to gently scrub the rust flakes from the metal. Flush the chemicals and dislodged rust from the metal with water.
Use minerals spirits as an alternative to the galvanised metal cleaner. Using the graduated step process as described prevents unnecessary damage to the galvanised metal in areas of light corrosion. Apply a zinc-based primer and zinc-based paint over the galvanised metal to protect it from corrosion.
Wear a respirator, safety goggles and protective gloves when removing corrosion from galvanised metal. Using wire wool and a wire brush on the underlying metal causes damages to the surrounding zinc layer if you scratch the zinc surface.