CUPA PIZARRAS Joins Industry Warnings about Risks of Metalutite

SUPPLIER of natural slate, CUPA PIZARRAS, has joined the industry in warning specifiers, roofers and homeowners about the risks of Brazilian metalutite.

It comes as the National Federation of Roofing Contractors’ (NFRC) issued a guidance note on the topic: GN66 Brazilian stone (slate).

Published on 1 October 2025, the document emphasises that Brazilian metalutite, commonly marketed as ‘Brazilian slate’, is a much weaker rock than true metamorphic slate. Products made from this lower quality material offer significantly poorer performance characteristics and longevity.

Industry Warnings

The publication adds to a growing body of industry commentators raising concerns about this issue. This includes a recent technical report from Cluster De Pizarras De Galicia, the Spanish slate association in Galicia, which highlights serious performance limitations associated with the material, including breakages, delamination and water absorption, leading to frost damage.

Steve Pearson, UK Director from CUPA PIZARRAS commented: “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. Now, with a unified industry position on this topic, contractors and specifiers can make informed decisions based on geological facts and the associated risks of using metalutite products.

“Clear industry guidance protects everyone – from roofers working with reliable materials to homeowners investing in roofs that will truly last.”

Misconceptions

Crucially, the growing industry focus on Brazilian metalutite shines a light on the misconception that it is a ‘slate’ and therefore a comparable material to genuine European slate – when they are entirely different rock types.

Genuine slate is a natural, metamorphic rock formed over millions of years. It is renowned for its durability, stability, and resistance to harsh weather. These qualities make it ideal for roofs in the UK and Ireland.

Brazilian metalutite, on the other hand, is a metalutite made from mudstone; a sedimentary stone that has been compacted over millions of years. However, it has not gone through the whole metamorphic process that true ‘slate’ has, which makes it extremely prone to breakage, delamination, and inconsistent thickness.

Reduced Longevity

Within its latest guidance note, the NFRC warns that Brazilian metalutite is “more brittle than European slates” and explicitly recommends hook fixing to reduce the risk of cracking and fracturing. Indeed, the guidance goes on to state that Brazilian metalutite has certain characteristics that can potentially reduce the longevity of the roof:

• Higher rate of water absorption, making it more vulnerable to the actions of freeze-thaw cycles.
• Brazilian slate is not a metamorphic rock and can lead to fractures and delamination, shortening the life of the product.
• The material is more brittle than European slates – additional care should be taken when handling during installation to avoid breakage.

This reflects the on-site experience of many within the roofing trade, with numerous reported cases of breakages, delamination, and tiles detaching in roofs using this lower quality material.

Indeed, the National House Building Council (NHBC) excluded Brazilian metalutite from its warranty as far back as 2012, highlighting the serious performance concerns in NHBC Technical Extra 07 (Jul 2012).

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