Cumaru — Density, Movement, Workability & Cost

Cumaru (Dipteryx odorata) and the tonka bean come from the same tree, which explains the faint vanilla scent that shows up when you cut this dense South American decking wood — an unexpected, genuinely pleasant surprise the first time a builder notices it, since nothing about a decking species' typical reputation suggests it should smell like a bakery.

The gentler alternative to ipe, mostly

Cumaru is usually specified as the direct alternative to ipe on a deck, and the comparison is fair — it's marginally softer than ipe, noticeably more interlocked in grain, and that interlock effectively rules out hand-planing altogether. A finished surface comes from a sander or a very careful power planer, never a hand tool, regardless of how sharp the iron is.

Movement, and a genuinely heavy deck-board weight

Radial shrinkage of 5.3% against a tangential figure of 7.7% gives a 1.5 ratio, reasonably contained for a species this dense. A 5.5"-wide deck board seasoning outdoors from a wet 18% down to a drier 12% — a realistic range for exterior installation — loses about 0.085" (2.2mm) across its width; check other widths and swings on the wood movement calculator. A 1"-thick, 5.5"-wide, 12-foot deck board weighs about 31.2 lb at cumaru's very high density — the wood weight calculator covers other decking sizes, worth checking before you plan to handle full-length boards without help.

Working around interlock and oil at once

The same caveats that apply to ipe apply here: oily and dense enough that adhesives shouldn't be trusted structurally on their own — mechanical fastening is the standard, reliable approach for decking construction regardless of what glue is used elsewhere in a project. Pre-drilling every fastener location isn't optional, since the interlocked grain makes splitting a real risk without it.

Durability, cost, and where it sits just under ipe

Cumaru's heartwood is very durable with good insect resistance, though it sits slightly below ipe specifically in ground-contact performance. At roughly $13 per board foot it's priced close to ipe, with the choice between the two often coming down to regional availability and the specific supplier rather than a clear performance gap. Decking, flooring, exterior joinery, heavy construction, and tool handles round out its markets.

A genus recently added to CITES, worth knowing about now

Dipteryx entered CITES Appendix II on 25 November 2024 after a two-year grace period, tagged with annotation #17 — expect permits on both rough boards and milled decking going forward. Tonka beans, harvested from the same tree for the flavour and fragrance industry, sit outside that annotation entirely, an odd but real split where two products from the same species face completely different regulatory treatment.

Choosing between cumaru and ipe

Where finish surface quality and hand-tool compatibility matter even slightly, neither wood is genuinely hand-plane-friendly, but cumaru's greater interlock makes it marginally worse in that specific respect. Where the deciding factor is straightforward availability, price, and general decking performance, the two are close enough that a builder's regular supplier often settles the choice more than any property difference does.

What people actually ask about cumaru

Does the vanilla-like scent in freshly cut cumaru fade once the deck board is installed and weathered outdoors? It fades fairly quickly under normal outdoor exposure — the scent is strongest right at milling and largely gone within the wood's first season outside, so it's a shop-floor curiosity during construction rather than a lasting feature of a finished installed deck.

Is there a sandpaper grit progression that works especially well for getting a smooth cumaru deck-board surface without a power planer? Starting coarser than a typical domestic hardwood — around 60 or 80 grit to knock down mill marks — before stepping through the usual progression handles cumaru's density better than trying to jump straight to a fine grit, since the density that resists a hand plane also loads and dulls sandpaper faster than a softer species.

Does the new CITES listing mean cumaru decking is now illegal to buy? No — an Appendix II listing regulates trade through permits rather than banning it, so legally documented cumaru continues to move through commerce; buyers should simply confirm a supplier has the correct paperwork for material sourced or imported after the listing took effect.

Cumaru isn't listed in the USDA Forest Products Laboratory's Table 4-4, so The Wood Database's 12%-moisture-content testing supplies density, Janka hardness and shrinkage here. CITES status is read from the appendices valid 5 March 2026.