Leading natural slate supplier CUPA PIZARRAS has welcomed NFRC’s latest guidance note – GN66 Brazilian stone (slate) – for clarifying the risks associated with Brazilian metalutite.
This is a rock often sold as ‘Brazilian slate’ but with very different properties from true metamorphic slate.
Published on 1st October 2025, the NFRC document highlights that Brazilian metalutite is a weaker, sedimentary rock formed from compacted mudstone rather than a durable metamorphic material. As a result, it is more brittle, prone to breakage, delamination and water absorption – all of which can compromise the roof’s longevity.
Steve Pearson, UK Director of CUPA PIZARRAS, said: “We are pleased to see the industry coming together in agreement about the risks of Brazilian metalutite and offering real clarity for specifiers, homeowners and roofing contractors.
“For too long, there has been confusion between genuine metamorphic slate and inferior metalutite products. Clear industry guidance protects everyone – from roofers working with reliable materials to homeowners investing in roofs that will truly last.”
The NFRC guidance recommends hook fixing to reduce the risk of cracking, and notes that Brazilian metalutite’s higher water absorption makes it more vulnerable to freeze-thaw damage.
As the world’s leading producer of natural slate, CUPA PIZARRAS continues to support the use of proven, high-quality materials that ensure roofs remain safe, durable and beautiful for decades.
