ROOFING contractors are investigating claims that thousands of stainless steel fasteners sold over the past two years could fail because of corrosion.
Laboratory tests in Germany showed that certain grades of rust-resistant stainless steel fixings failed in alternating corrosive conditions.
The flaws were revealed by the staterun Materials Testing Institute in Darmstadt. Researchers found that up to 90 per cent of the most widely sold grade of selfdrilling screws, made from modified martensitic stainless steel, suffered stress corrosion cracking.
Sales of this type of fastener, imported from the Far East, have soared in recent years because rust resistance offers big savings over the lifetime of a building.
But the tests revealed that these cheaper fixings are prone to sudden failure when put into tension after being used to fix metal cladding or roofing.
The report concluded: 'Fasteners manufactured from modified martensitic stainless steel represent a safety risk in building practice even if corrosion resistance requirements are minimal.'
A spokesman for the National Federation of Roofing Contractors said: 'It would be unwise to make a rash judgement, but we are looking into various types of stainless steel.'
A committee drawing on experts in the fastener and fixings industry will look at the evidence in the coming weeks.
The results have shocked the fastener industry, though distributors of the screws say they have been used in the US for more than 20 years without problems.
Andrew Meese, technical manager of UK fastener maker EJOT, said: 'What is worrying is corrosion is not apparent until the screw head literally snaps from the screw shank.'
UK manufacturers use the safer austenitic stainless steel but the more complex process means the fasteners can cost a third more than imported fasteners.
A spokesman for EJOT said: 'An enormous quantity of martensitic stainless steel fixings is available in the UK, so this report will be of interest to all specifiers and contractors involved in the cladding, roofing and window industries. We are concerned that all stainless steel fasteners will be tarred with the same brush.'