Terne coated finishes on stainless steels
Terne coatings can be applied to carbon and stainless steels. They are usually done on sheet or strip for external cladding, roofing, flashings etc. building applications. 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.
Definition of terne coating
Terne coated stainless steels are defined in BS EN 502 and BS BS EN 508-3 as 'stainless steel continuously hot dip coated with a lead-tin alloy'. These standards 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 BS 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.
Grades and standards
BS EN 502:2000 covers 'Roofing products from metal sheet-Specification for fully supported products of stainless steel sheet'
BS 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'
BS EN 502 allowable grades include ferritic and austenitic grades
The major suppliers tend to supply either 1.4301 (304) or 1.4401 (316) substrate strip grades with either terne or electrodeposited tin coatings.
Suppliers of coated stainless steel strip
BSSA member companies supplying these coated strip products include :
ArcelorMittal Sheffield Stainless Service UK, contact Kevin Jones