Profiled metal roofing – swarf staining

Cause

Swarf (residual fragments of steel from cutting, drilling or grinding roofing sheets) have been left on the roofing or in gutters

Repair

  • if the swarf was produced during installation or repair of the roof in recent years, call the installer/repairer back to clean up. The NZ Metal Roofing Manufacturers’ Installation Guide for Metal Longrun Roofing and Cladding (version 1.0 May 2022) says: “All debris must be swept off the job at the end of each day. Prevention of swarf damage is far easier than its cure.”
  • if the installer is no longer available, ask the roofing supplier or manufacturer (if known) for advice
  • it may be possible to remove very mild staining with a soft brush or cloth and water with mild detergent. If necessary, use a nylon pot cleaner. Do not use a wire brush or anything likely to scratch the surface of the roofing
  • if the staining is severe and not removed by cleaning attempts, ask the roof cladding manufacturer or supplier for advice and product recommendations for dealing with the stains. Where the coating is severely damaged by swarf corrosion, manufacturers often recommend that the whole area that is affected should be painted or replaced
  • if you paint the roof, ensure swarf is completely removed before painting. Particles that remain and are painted over may lead to rust bleed-through
  • be aware that air drying paints may weather faster and in a different way to pre-painted roofing. Limiting painting to small areas may lead to a messy and visually unacceptable difference in appearance between painted and unpainted roof areas at a later date
  • while sunscreen gives important protection while working on a roof, do not use sunscreen containing titanium dioxide or zinc oxide. These substances can cause irreparable damage to some factory finished roofing surfaces
  • always tell someone else when you plan to work on a roof and take the appropriate safety precautions. You can find details here