Working with Cumaru: Tips for Builders

Handling the High-Shrinkage Champion

Cumaru offers Ipe-like density and durability, but its interlocked grain and higher shrinkage rate demand specific installation methods. Understanding how Cumaru moves is the key to a successful, long-lasting deck.

Recommended Tooling

Like Ipe, Cumaru requires premium carbide-tipped blades and router bits. Because of its highly interlocked grain, routing can be prone to tear-out. Ensure your cutting edges are razor-sharp and take multiple shallow passes rather than one deep cut.

Cutting & Routing

Feed slowly to avoid burning the wood and dulling the blade. The interlocked grain means the wood can behave unpredictably during ripping, occasionally pinching the blade. Use wedges if necessary. Always seal the cut ends immediately to prevent checking.

Pre-Drilling

Pre-drilling is mandatory. Use sharp cobalt or HSS bits. Because of the wood's density, you must clear the hole of debris frequently while drilling to prevent the bit from binding and snapping.

Fastening

Cumaru has a higher tendency to cup or twist than Ipe as it acclimates. For profiles wider than 4" (like 1x6 or 5/4x6), face-screwing with two high-quality 316 stainless steel screws per joist is strongly recommended over hidden clips to physically restrain the board.

Health & Safety

Cumaru dust has a distinct vanilla/cinnamon scent, but it is a fine particulate that can irritate the respiratory system and eyes. Some individuals may experience skin irritation. Proper PPE, including respirators and eye protection, is required during cutting and sanding.

Pro Tips from the Field

Strict 14-day on-site acclimation is critical for Cumaru. Do not skip this step.
Ensure excellent under-deck ventilation. Cumaru needs airflow to balance moisture content on all sides.
When planning layout, keep board lengths manageable; shorter boards are easier to force straight if they have slight bowing.
If using hidden fasteners on 1x4 Cumaru, use a system that screws through the clip into the board to help hold it flat.

Need Project-Specific Guidance?

Our hardwood experts are available to consult on tricky installations, material takeoffs, and custom milling requirements.