Zinc
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Rust on zinc/aluminium or aluminium/zinc alloy-coated steel roofing
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Erosion of or scratching damage to the zinc/aluminium or aluminium/zinc alloy coating, exposing the steel
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Lack of rain washing. Rain washing tends to be less effective on roofs with less than 15 degrees slope
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Roofing metal is in contact with or has run-off from cedar or redwood, or timber treated with a copper-based preservative treatment
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Roofing has run-off from translucent (PVC) sheeting
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Corrosion of the steel in a corrosive environment such as near a swimming pool, or in coastal, industrial or geothermal regions
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Inadequately primed end and/or side laps
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Use of lead flashings
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The roofing is near the end of its serviceable life
Rust on alloy-coated pre-finished steel roofing
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Paint failure and subsequent erosion of or scratching damage to the zinc/aluminium or aluminium/zinc alloy coating, exposing the steel
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Roofing material is in contact with or has run-off from cedar or redwood, or timber treated with a copper-based preservative treatment
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The roofing has run-off from translucent (PVC) sheeting
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The roofing is near the end of its serviceable life
Metal tile roofs – corrosion
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Loss or breakdown of the stone chip coating or paint coating
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Air-borne salt accumulating under tiles, particularly where tiles are damaged
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Erosion of the galvanising, zinc/aluminium or aluminium/zinc alloy coating, exposing the base metal
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Roofing at the end of its serviceable life
Zinc roofing – white surface corrosion
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Lack or rainwashing. Rain washing tends to be less effective on roofs with less than 15 degrees slope
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The roofing material is in contact with, or has run-off from, cedar or redwood, or timber treated with a copper-based preservative treatment
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The roofing has run-off from translucent (PVC) sheeting
Zinc roofing – buckling
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Thermal movement in the roofing is not being accommodated by the fixing system
Zinc roofing – bent seams or joints
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Foot traffic on the roof
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The panels were damaged when installed
Zinc roofing – uneven colour
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Some parts of the roof area are more exposed to the weather or rainwashing, which slows the development of the traditional zinc oxide on the surface
Zinc roofing – holes
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Condensation is forming on the back of the zinc panels – pure water is very damaging to zinc
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Corrosion is initiated through the use of the wrong fixings
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The zinc is not isolated from the plywood substrate
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CCA (copper-based) treated plywood has been used
Corroded metal roof flashings
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Air-borne salt, dust or dirt accumulating under flashings
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The paint finish has deteriorated, exposing steel
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Loss or breakdown of stone chip coating (pressed metal tile roofing flashing)
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Loss of galvanising or zinc/aluminium alloy coating exposing the base metal
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Run-off from incompatible materials such as glass or plastic roofing
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Run-off from cement-based mortar (tiled roofs)
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Acidic run-off from uncoated cedar wall cladding
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Debris or swarf (metal filings and chips) accumulated in valley gutters
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Moisture being held within the lapped joints
Roof flashing leaks
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Poor initial installation
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Inadequate cover at laps
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Joints are not sealed
Profiled steel cladding – corrosion: white rust
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Corrosion of the zinc when water is trapped between sheets at laps and joints, or during storage prior to installation
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Insufficient rain washing
Corrosion: red rust on galvanised mild steel cladding
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Galvanised coating has eroded to expose bare metal
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Profiled metal cladding is in contact with or has run-off from cedar or redwood, or timber treated with copper-based preservative treatment
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Galvanised mild steel cladding has run-off from translucent sheeting (PVC), glass, pre-painted roofing, glazed tiles, unpainted zinc/aluminium alloy-coated mild steel or aluminium
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Damage to the galvanised coating during fixing exposing steel
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Exposure to a corrosive environment such as a swimming pool, or in coastal, industrial or geothermal areas
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Inadequately primed end and/or side laps
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Cladding in ground contact
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Insufficient rain washing
