Black Locust
Robinia pseudoacacia
Hardness
Hard and durable; stands up to wear and traffic.
Overview
One of the most rot-resistant woods on earth and brutally hard, a domestic answer to tropical decking. Tough to work but lasts for decades outdoors.
Commonly built
- Fence posts
- Outdoor benches
- Decking
- Trellises
Appearance
Greenish-yellow to golden-brown, darkening to a richer brown with age. Coarse but attractive grain.
Recommended uses
Uses to avoid
Similar species
Comparable on hardness, type, and workability, useful when this species isn't available.
Working notes
Very hard and dense, hard on tools and prone to tearout. Outstanding decay and insect resistance makes it ideal outdoors. Excellent fence posts and ground-contact use.
Wood movement
A 24-inch-wide flatsawn black locust panel moves roughly 0.39 inch across a typical seasonal humidity swing (about 6% to 12% moisture content). Use the wood movement calculator to run your own board size and moisture range.
How much does Black Locust move? → See flatsawn vs. quartersawn figures and a worked example.
Common questions
How hard is Black Locust?
Black Locust has a Janka hardness of 1700 lbf, a measure of how well it resists denting and wear.
Is Black Locust suitable for outdoor use?
Black Locust stands up reasonably well outdoors, especially with a protective finish and regular maintenance.
How easy is Black Locust to work with?
Black Locust has Fair workability for cutting, shaping, and joinery.
How much does Black Locust move seasonally?
A 24-inch-wide flatsawn black locust panel moves roughly 0.39 inch across a typical seasonal humidity swing (about 6% to 12% moisture content).
Finishing notes
Very hard and dense, so finish penetrates slowly; its natural rot resistance means it is often left unfinished outdoors, weathering to gray. Takes an exterior penetrating oil or stain well when finished. The greenish-yellow color ages to a warm brown under UV. Open grain can be filled for a smooth indoor film finish. Use non-corroding fasteners; like other durable woods it can react with iron.
Community photos
Real photos from woodworkers who've used black locust, reviewed before they appear here.
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Wood data varies by source and sample. How we source and review our data.