Terne coating can be applied to
carbon steel and stainless steel. They are usually done on sheet or strip for external cladding, roofing, flashings etc. building application. Terne coating confers a lead patina appearance to the steel
surface and so can be used as a substitute for solid lead sheet roofing to buildings such as churches.
Terne coated stainless steel are defined in EN 502 and EN 508-3 as 'stainless steel continuously hot dip coated with a lead-tin alloy'. These standard also cover 'tin coated stainless steel' as 'stainless steel continuously coated with tin by electrodeposition'.
The normal stainless steel 'substrate' strip thicknesses range from 0.4 to 0.8 mm in EN 502. These have a specified minimum coating mass of 20 gm/m2 for hot dipped terne coatings or 10 gm/m2 for tin coatings. They are laid on timber substrates, usually with underlays to reduce noise. Standing or batten-roll jointing systems are most common.
Advantages of terne coated stainless steel
These strip materials are therefore much lighter than traditional lead roofing systems and so can result in lighter support structure cost savings. 'Creep' of the cladding will not occur as it may do with lead sheeting and so should be more stable. Tern coated sheet should also be more difficult to remove once installed and so less likely to be stolen.
EN 502:2000 covers 'Roofing products from metal sheet Specification for fully supported products of stainless steel sheet'
EN 508-3:2000 covers 'Roofing products from metal sheet Specification for self-supporting products of steel, aluminium or stainless steel sheet - Part 3: Stainless steel'
The major suppliers tend to supply either 1.4301 (304) or 1.4401 (316) substrate strip grades with either terne or electrodeposited tin coatings.
