Advanced Timber Knowledge

Cumaru: The perfect material for external seating?

What is Cumaru?

Cumaru is a tropical hardwood primarily cultivated in Central and South America. It possesses natural oils and boasts high density, making it a versatile timber used for various applications. Notably, its exceptional durability has led to its utilization in street furniture, where it enjoys a Class 1 durability rating, indicating a potential lifespan of up to 90 years. Another tropical hardwood with a similar durability rating is Opepe.

Is Cumaru a Suitable Choice for Seating and Street Furniture?

While it is commonly employed in external seating, such as curved terrace and wall top seats, its suitability merits consideration.

Advantages:

Class 1 Durability Rating: Cumaru’s durability rating surpasses that of many other tropical hardwoods, including Iroko.
High Density: Its density lends it strength and resilience.
Natural Oil Content: Cumaru’s high oil content offers a degree of natural pre-treatment, akin to other tropical hardwoods.
Attractive Appearance: When freshly cut, Cumaru exhibits appealing aesthetics; however, like all timber, it weathers over time to a uniform silvery-grey patina.
Resistance to Pests: Cumaru demonstrates good resistance to termites and other dry-wood borers.

Disadvantages:

Environmental Impact: Its high carbon footprint arises from the need to transport it from its growth regions, primarily Central America or Western Africa.
Workability Challenges: Cumaru’s density and silica content make it challenging to work with.
Adhesive Issues: Gluing can be problematic due to the natural oils in the timber.
Susceptibility to Cracking: Cumaru tends to crack and check as it dries, creating safety hazards from splinters.
Leaching Sap: The dark brown sap may leach onto surrounding surfaces in public realm projects, leading to maintenance issues.

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Conclusion:

Selecting Cumaru for external street furniture is not recommended due to several drawbacks. While its durability rating is an advantage, it is outweighed by the risk of cracking, leaching tannins, and its negative environmental impact. Each tree takes more than 150 years to grow, and the extensive carbon emissions associated with transporting it from growth areas to the UK apply to all tropical hardwoods.

Despite these concerns, tropical hardwoods are still favoured for street furniture due to their remarkable durability and smoothness resulting from their oil content. However, Logic does not endorse the use of tropical hardwoods due to their environmental unfriendliness. In cases where their use is mandated, Opepe is a preferable choice over Cumaru and Iroko. Opepe is cost-effective, less prone to cracking, and available as FSC® certified, offering some assurance of sustainable sourcing.