Red rust on zinc/aluminium or aluminium/zinc alloy-coated steel

Cause

Corrosion of the steel when zinc/aluminium alloy coating has eroded to expose the steel

Repair

  • sand the corroded areas to remove rust; prime with a zinc-rich primer and a metal primer, repaint applying a minimum two coats of acrylic paint, or in accordance with the manufacturer’s recommendations
  • replace badly corroded sheets; ensure the new material is compatible with surrounding materials

Cause

Cladding material in contact with or has run-off from cedar or redwood, or timber treated with a copper-based preservative treatment 

Repair

  • sand the corroded areas to remove rust; prime with a zinc-rich primer and a metal primer, repaint applying a minimum two coats of acrylic paint, or in accordance with the manufacturer’s recommendations
  • replace badly corroded sheets; ensure the new material is compatible with surrounding materials

Cause

Cladding has run-off from translucent (PVC) sheeting 

Repair

  • sand the corroded areas to remove rust; prime with a zinc-rich primer and a metal primer, repaint applying a minimum two coats of acrylic paint, or in accordance with the manufacturer’s recommendations
  • replace badly corroded sheets; ensure the new material is compatible with surrounding materials

Cause

Corrosion of the steel in a highly corrosive environment such as a swimming pool, or in coastal, industrial or geothermal regions

Repair

  • sand the corroded areas to remove rust; prime with a zinc-rich primer and a metal primer, repaint applying a minimum two coats of acrylic paint, or in accordance with the manufacturer’s recommendations
  • replace badly corroded sheets; ensure the new material is compatible with surrounding materials

Cause

For factory coated material, wrong coating specification for the in-use conditions

Repair

  • sand the corroded areas to remove rust; prime with a zinc-rich primer and a metal primer, repaint applying a minimum two coats of acrylic paint, or in accordance with the manufacturer’s recommendations
  • replace badly corroded sheets; ensure the new material is compatible with surrounding materials

Cause

Inadequately primed end and/or side laps

Repair

  • sand the corroded areas to remove rust; prime with a zinc-rich primer and a metal primer, repaint applying a minimum two coats of acrylic paint, or in accordance with the manufacturer’s recommendations
  • replace badly corroded sheets; ensure the new material is compatible with surrounding materials

Cause

Cladding in ground contact

Repair

  • sand the corroded areas to remove rust; prime with a zinc-rich primer and a metal primer, repaint applying a minimum two coats of acrylic paint, or in accordance with the manufacturer’s recommendations
  • clear away ground in contact with the cladding; excavate adjacent soil to lower the ground level; slope ground away from the building
  • replace badly corroded sheets; ensure the new material is compatible with surrounding materials

Cause

Insufficient rain washing 

Repair

  • sand the corroded areas to remove rust; prime with a zinc-rich primer and a metal primer, repaint applying a minimum two coats of acrylic paint, or in accordance with the manufacturer’s recommendations
  • replace badly corroded sheets; ensure the new material is compatible with surrounding materials