Metal elements such as roofing, fixings and flashings may have corroded and need replacement.
Metal windows, roofing, claddings, fixings, flashings or accessories (hinges) may be corroded. This is more likely to be a problem closer to the coast and in geothermal regions, and in industrial areas. It is also more likely to be a problem for metal components that are not rain washed or cleaned regularly.
Corrosion is caused by:
- moisture combined with salt spray, dirt, or hydrogen sulphide from coal-burning fires or geothermal activity
- contact between dissimilar metals resulting in electro-galvanic action.
It may appear as red rust in metals containing iron, or as a white discolouration on the surface of materials containing zinc.
The parts of houses built in coastal regions most likely to be affected are the subfloor and cladding fixings and roof, window and door flashings and door and window hinges. Any components that are significantly affected by corrosion such as with pitted or pinholed surfaces, should be replaced.
Corrosion may be found in metal components such as fixings, flashings and other accessories, particularly near the sea, in geothermal or industrial areas, and where. It may appear as red rust in metals containing iron, or as a white discolouration on the surface of materials containing zinc.
Also see wall claddings.
Where corrosion on mild steel is on the surface only it can be removed by:
- sanding with grit paper to expose shiny metal
- priming with a zinc-rich primer
- applying a solvent-borne metal primer
- applying two finish coats.
The risk of corrosion is reduced by:
- painting steel
- specifying factory-coated steel with a coating suitable for the environment
- using hot-dip galvanised steel or stainless steel fixings, brackets and hinges.
Rust may chemically attack timber around corroded fastener – this is referred to as ‘nail sickness’. It presents as dark staining around nails in older timber and although it is unsightly and indicates a slightly weakened part of the timber, it does not generally pose a structural risk.