Material notes: Cumaru

Cumaru (Dipteryx odorata) is a Brazilian hardwood with a specific gravity of around 1.09 — it sinks in water, which tells you something about its density. It is classified as Class A for durability, meaning it can be used in ground contact or in permanently wet conditions without treatment.

We have used it on four projects now: as decking at Casa Pinheiros, as structural louvres at Casa Brava, as exterior joinery at Casa Maresia, and as an interior wall cladding at Interior Jardins. Each application has taught us something different about the material.

What we have learned: cumaru wants to move. It is a very dense wood but it still has seasonal movement, particularly in the tangential direction. Gaps between deck boards need to be generous — we specify 6mm — and any fixed connection should allow for this movement or the boards will cup. In exterior use, new cumaru is a warm mid-brown; after six months of UV exposure it fades to a silvery grey that we find more interesting than the original colour. Clients sometimes panic at this; it is worth warning them in advance.