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Cumaru Deck Installation Guide
Everything you need to install Cumaru (Brazilian Teak) decking — joist spacing, board gaps, acclimation, fastener rules, pre-drilling, and species-specific tips.
Janka Hardness
3,330 lbf
Fire Rating
Class A
Lifespan
50+ years
Density
63 lbs/ft³
Cumaru Wood Properties for Installation
Pre-Drilling
Required — always
Workability
Difficult — very dense, similar to Ipe but slightly more forgiving
Color
Warm reddish-brown to golden-brown tones, weathers to silver-gray.
Tannin Bleed
Moderate tannin bleed, especially when wet. Temporary and decreases over time. Clean with oxalic acid if needed.
Blade Note
Use carbide-tipped blades. Cumaru is slightly easier on tools than Ipe.
Joist Spacing for Cumaru Decking
Board Spacing for Cumaru
Between Boards
3/32"
End Gap (Structures)
1/8" from fixed structures
Airflow Under Joists
18" minimum unobstructed air under joists
How to Acclimate Cumaru Before Installation
Allow 7–10 days for Cumaru to acclimate to your local climate before installation. Store boards on blocks at least 12" off the ground with proper ventilation between layers. Cover with plywood — never plastic or tarps.
Climate Note
Cumaru performs well across all US climates. Its natural oil content provides excellent moisture resistance. Allow extra acclimation time in coastal or high-humidity areas.
Fasteners for Cumaru Decking
- Fastener type: Stainless steel only (304 or 316 grade).
- Edge distance: 3/4" minimum from board edges
- Pre-drilling: Required — always
Cumaru Installation Tips
Pre-drill all holes — Cumaru is nearly as dense as Ipe
Expect tannin bleeding on nearby surfaces during the first few months
Seal all fresh end cuts within 24 hours
Allow extra acclimation time in humid climates
Use hidden fastener clips with pregrooved boards for a clean finish
Protect adjacent concrete/stone from tannin stains with drop cloths during install
Common Cumaru Installation Mistakes
Not accounting for tannin bleed on adjacent surfaces
Skipping pre-drilling — just as critical as with Ipe
Rushing acclimation in humid regions
Using galvanized fasteners — causes severe black staining
Insufficient end-grain sealing
Installing boards too tight — Cumaru expands/contracts with moisture
Build Your Custom Installation Plan
Get a printable, jobsite-ready plan with fastener spacing, joist layout, and climate-specific guidance.
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Cumaru Installation FAQ
Common questions about installing Cumaru decking.
For 1×4 and 1×6 Cumaru boards, maximum joist spacing is 16" on center max. For 5/4×6, you can go up to 24" on center max. For 2×6, up to 32" on center max. Always verify with your local building code.
Required — always. Cumaru has a Janka hardness of 3,330 lbf, which makes it essential to pre-drill to prevent splitting and broken fastener heads. Use brad point or Forstner drill bits for the cleanest holes.
Allow 7–10 days for Cumaru to acclimate to your local climate. Store on blocks 12" off the ground with proper ventilation. Cover with plywood (NOT tarps or plastic). For a customized estimate, use our Acclimation Calculator.
Stainless steel only (304 or 316 grade). Never use galvanized fasteners with Cumaru — they cause black staining and corrosion. For a clean look, use pregrooved Cumaru boards with hidden fastener clips.
Leave 3/32" between Cumaru boards for ventilation and expansion/contraction. Leave 1/8" from fixed structures from fixed structures like walls or posts.
Cumaru decking can last 50+ years outdoors with proper installation and minimal maintenance. It's Class Class A fire rated and naturally resistant to rot, decay, and insects.
Cumaru requires more care than softwood or composite due to its density (3,330 lbf Janka). Difficult — very dense, similar to Ipe but slightly more forgiving. With the right tools (carbide-tipped blades, stainless steel fasteners) and pre-drilling, both DIYers and contractors install Cumaru successfully.