Brazilian Slate

Brazilian slate is stone quarried mainly in the state of Minas Gerais, which accounts for about 95% of Brazil's slate extraction, particularly around Papagaios. Brazil is the world's second-largest slate producer after Spain.

Geology

Brazilian slate differs from most European and North American roofing slates. It is generally described as a sedimentary-derived rock that splits along its original bedding planes rather than along a metamorphic cleavage. This affects how thinly and evenly it can be split and how it behaves when wet and frozen.

Performance as roofing

A Spanish-led comparative study found that Brazilian slate had higher water absorption than Galician roofing slate and lost significant strength under freeze-thaw cycling, making it less suitable for roofing in cold climates. Some Brazilian products sold in the United Kingdom have been reported as not entitled to the CE mark for roofing use. European producers have also questioned the suitability of some imported slates for roofing.

Uses

Freeze-thaw weakness matters most in cold, wet climates; in frost-free regions the same limitation is less significant, and slate from Brazil is also used for non-roofing purposes such as paving and cladding.

Specification advice

Anyone considering imported slate for a roof in a frost-prone region should ask for test results to the relevant national standard, such as EN 12326 in Europe or ASTM C406 in North America, rather than relying on origin or appearance.

Other imported slates

China also has vast slate deposits, and its exports of finished and unfinished slate have grown in recent years. As with Brazilian material, the suitability of any imported slate for roofing depends on its test results rather than its country of origin.