An increase in incorrectly marked, inferior slate coming into the UK market poses a worrying threat to merchants and contractors, SIG Roofing Supplies has warned.

Following the recent collapse of the slate market in France and the desperate bid by some Spanish quarries to make up their volumes elsewhere, rust-risk (effectively T2) slates are being badged and sold as T1 slate.

SIGA’s slate category manager Joe Bordas explained: “Concern is escalating regarding this situation, as UK roofers are being duped into thinking they have a genuine bargain. Not only are roofers being deliberately misled, these slates are often ones our experienced buyers have already investigated, considered, and turned down due to excessive risk; either in the rock used or commercially.”

According to SIG, the problems caused by using inferior natural slate have long been a challenge to the roofing industry – not only can the slate be riddled with inconsistencies and imperfections that result in high wastage, it also often translates into higher labour costs too.

“It’s bad enough that the slate is actually inferior, but being duped into believing that the slate is high-quality T1 slate is appalling,” Mr Bordas commented. “When the roof rusts, getting restitution is exceedingly difficult, with some importers refusing to accept there are problems – leaving the contractor with the choice of swallowing the costs of reroofing, or taking legal action.

“Slate should always be selected from a reputable supplier and a copy of the BS EN12326 Declaration of Performance obtained. This will enable the key physical properties of the slate to be compared in order to ensure it’s up to the job in hand. The most critical areas are frost resistance, visible rusting, and structural integrity, and these are all covered by the Declaration of Performance.”

From this month, it will be even more critical to ask for BS EN12326 certification and CE crate labelling; Local Authority Building Control will be looking for this on all products to which the Construction Products Regulation applies, including natural slate.

Bordas continued: “The growing trend for extended warranties compounds the problem further. Roofers think they are being offered a safety net, but sadly most of the companies won’t be around anywhere near long enough to honour their promises. Most slates are 500 million years old to start with, but only highly experienced importers will know how the rock will fare once split and laid on a roof.”

SIG Roofing cautions that when choosing natural slate, it is now more important than ever not to cut corners, and to insist on best value – not just the best price. In the same way householders expect to see examples of a roofer’s previous work, roofers and architects should view or visit sites roofed with the proposed slate, particularly given the initial cost of natural roofing.

SIG Roofing currently sells over 13m slates a year across the UK via its SIGA collection. Largely sourced direct from quarries located all over the world in major slate producing countries such as Spain, Wales, China and Canada, the SIGA range meets the key essential criteria of BS EN12326 test results and certification, CE labelling, consistency and security of supply, and consistency of quality.

Bordas concluded: “More than with any other roofing material, with natural slate you get what you pay for. There is always cheap slate around, but there will always be a reason that it’s cheap, so roofers need to buy with their eyes wide open. In the long run, the client will thank you for it.”