Acacia wood has become increasingly popular for furniture, flooring, decking, and other applications in recent years. This dense hardwood is prized for its extreme hardness and durability, making it well-suited for high-traffic areas in both residential and commercial spaces. But just how hard is acacia wood compared to other popular species of lumber? Let’s examine the facts and figures to gain a true understanding of acacia’s hardness.
What is Acacia Wood?
Acacia is the name for a genus of small trees and shrubs with over 1,300 species native to Australia, Africa, Asia, and the Americas. There are approximately 1000 species native to Australia, where most acacia lumber for commercial use is harvested.
Some of the most common species used in woodworking and construction include:
- Australian Blackwood (Acacia melanoxylon)
- Cootamundra Wattle (Acacia baileyana)
- Sydney Golden Wattle (Acacia longifolia)
- Silver Wattle (Acacia dealbata)
Acacia trees and shrubs are fast-growing, meaning lumber can be harvested commercially in as little as 8-10 years. The wood has a distinctive figured grain with varied colors ranging from golden brown to reddish brown.
Acacia wood is highly sought-after for its density, hardness, attractive grain patterns, and sustainability as a fast-growing renewable resource. But it’s the hardness that makes it stand out from most other commercially available lumber.
Acacia’s Janka Hardness Rating
The most common way to measure the hardness of wood is using the Janka hardness test. This measures the force required to embed a 0.444″ steel ball into the wood to half its diameter. The result is measured in pounds-force (lbf).
According to the Janka hardness scale, acacia wood has a rating of 2300 lbf. This makes it an extremely hard wood, especially compared to more common species used in furniture and flooring:
- Oak – 1,220 lbf
- Maple – 1,450 lbf
- Cherry – 950 lbf
- Walnut – 1,010 lbf
- Pine – 690 lbf
As you can see, acacia is significantly harder than all of these woods, which are considered hardwoods in their own right. Hard maple is the only domestic wood that comes close, which is still 37% softer than acacia.
Some examples of how acacia’s hardness compares:
- Acacia is 55% harder than white oak
- Acacia is over 20% harder than hickory
- Acacia is nearly 1.5 times harder than mahogany
- Acacia is over 3 times harder than pine, a softwood often used in furniture
So exactly how hard is 2300 lbf? Consider that most exotic tropical hardwoods have a Janka rating between 2000-3000 lbf. Australian cypress, one of the hardest woods on earth, rates at 3,680 lbf.
While not quite in the same league as those tropical hardwoods, acacia is relatively close in hardness, making it stand out as an unusually hard wood from a temperate climate.
Benefits of Acacia’s Hardness
Several notable benefits come with acacia’s exceptional hardness rating:
Scratch Resistance
The dense cell structure and hardness make acacia resistant to scratches, scuffs, and dents. When used for tabletops, floors, or other high-traffic areas, acacia will stand up to wear and tear better than softer woods. The surface resists dings and abrasions that quickly make oak, pine, or other woods appear worn and weathered.
Stability
With its dense grain, acacia wood is less prone to warping and cupping than many other woods. Harder woods tend to be more dimensionally stable, meaning furniture, floors, and other items retain their shape over years of use. There is very little expansion or contraction with seasonal changes in temperature and humidity.
Long-Lasting
The hardness and natural resistance of acacia wood contributes to its long lifespan. Acacia’s density helps it stand up to weather, sunlight, and wear when used for outdoor furniture, decking, or other exterior applications. Its natural oils and resins also create a certain level of rot and insect resistance. Properly finished and maintained, exterior acacia wood can last over 25 years.
High Traffic Areas
From living rooms to restaurants to hotels, acacia is an ideal wood for any high-traffic area. The combination of hardness, scratch resistance, and stability make it suitable for withstanding heavy daily use without showing excessive signs of wear and tear. Table tops, floors, and surfaces keep their like-new appearance for years.
Challenges Working with Acacia
Despite its many benefits, acacia’s extreme hardness does present some unique challenges when it comes to working with this lumber:
Difficult to Cut and Shape
The density of acacia makes it very difficult to cut and shape with hand tools. The hardness is comparable to exotic tropical woods that are notoriously challenging to mill by hand. Power tools and sharp blades are a must. Special carbide-tipped blades may be required to avoid excessive wear when cutting acacia.
Prone to Splintering
While it can be shaped into graceful curves and details, acacia’s hardness also makes it prone to splintering if tools become dull or proper precautions aren’t taken. Care must be taken when sawing, routing, chiseling, or sanding to avoid splintering on the surface. Using sharp bits and taking it slow helps mitigate this issue.
Can Be Unforgiving
The hardness and density of acacia means it does not flex easily. For woodworkers used to working with more forgiving softwoods, adjusting techniques to account for acacia’s rigidity takes practice. A softer touch and more precise cuts are required to achieve clean results and avoid tear out.
Difficult to Nail and Screw
Driving fasteners into acacia can be difficult due to its density and hardness. Pre-drilling pilot holes is strongly recommended. Using self-tapping wood screws designed for hardwoods makes fastening acacia boards much easier. Specialty nails may also be required.
Hard on Tooling
Working with acacia will wear down tooling faster than normal. The abrasive nature of this hardwood will take its toll on table saw blades, router bits, planer knives, and other tools. Be prepared for reduced tooling life and increased costs associated with resharpening or replacing tooling.
Not Ideal for Delicate Work
A softer wood may be preferable when dealing with finicky, delicate woodworking requiring intricate carving, bending, or joinery work. Acacia’s hardness and rigidity does not lend itself well to detailed shaping or projects where flexibility and forgiveness in the wood is an asset.
How Does Hardness Impact Cost?
Due to its exceptional hardness, acacia lumber costs more than traditional North American hardwoods, including oak, maple, cherry, and birch. Prices can be 20-50% higher per board foot. There are a few reasons for acacia’s higher cost:
- Imported lumber: Much of the commercially sold acacia comes from sustainable plantations in Australia and is exported to North America, increasing costs.
- Processing difficulties: Milling and working with acacia is more labor-intensive due to its hardness. This drives up processing costs which translates to higher prices.
- Wear on tooling: The rapid dulling of saw blades, planer knives, and other machining equipment makes processing less efficient and more costly, increasing the final price.
- Rarity: Acacia is still relatively less common than domestic hardwoods. Exotic woods typically command higher prices based on rarity and import costs. The unique properties and look of acacia make it worth the premium price for many.
However, acacia wood’s extreme hardness and durability provide great value when viewed through a long-term lens. The extended lifespan and reduced maintenance needs compared to softer woods offset some of the higher initial investment.
Is Acacia Suitable for Outdoor Use?
The hardness, weather resistance, and longevity of acacia wood make it a suitable choice for outdoor and exterior applications. Here are some pros and cons to consider when using acacia outdoors:
Pros:
- Hardness resists dings, scratches and dents from outdoor use.
- Density and stability minimizes cupping, twisting, and warping from weather.
- Natural oils provide a degree of moisture, rot, and insect resistance.
- Attractive appearance enhances outdoor living spaces with interesting grain.
- Can last over 25 years outdoors with proper maintenance.
Cons:
- Not as resistant to weathering as naturally durable species like cedar, teak or ipe.
- Still requires protective finish and periodic refinishing when used outside.
- Surface may develop some checking, greyish patina.
How Does Hardness Affect Workability?
Acacia’s exceptional hardness makes working more challenging than traditional domestic hardwoods. The density, strength, and rigidity require specialized tools, techniques, and precautions to successfully mill and fabricate acacia lumber.
Cutting and Shaping
Ripping, cross-cutting, mitering, routing, shaping, and sanding acacia are more difficult than working softer woods. The challenges include:
- Slow feed rates required to avoid overheating blades and bits. Taking it slow is a must.
- Carbide-tipped tooling often necessary for optimal results and longevity of blades.
- Pre-drilling all holes to prevent splitting when nailing or screwing. Pilot holes are a must before inserting fasteners.
- Clamping with cauls and other precautions to minimize splintering when sawing or routing.
- Sharpening blades and bits more frequently to maintain razor sharp cutting edges.
Joinery and Assembly
The techniques used to join and assemble acacia wood projects also are affected by its hardness:
- Pocket holes and other mechanical joinery work well with acacia since nails/screws can be problematic.
- Most standard wood glues bond successfully with acacia. Polyurethane and epoxy are extra-strong options.
- Care should be taken to avoid cracking or splitting when using press joinery techniques like biscuits or dowels.
- Allow ample clamping time for glue to cure properly when joining acacia boards and panels.
Finishing Recommendations
Applying protective finishes and stains to hard, dense acacia requires adjustments as well:
- Pre-sanding with up to 120 grit may be advisable to open the pores before staining.
- Conditioners can help staining take more evenly on denser woods like acacia.
- Oil-based stains and wiping stains tend to perform better than water-based options.
- Film-building finishes like polyurethane provide maximum protection. Oils give minimal protection on harder woods.
- Allow 50% longer drying times between finish coats to account for the density and hardness of the wood.
In Summary
Regarding hardness, acacia wood sits in a class of its own. With Janka hardness ratings over 50% higher than oak and more than 20% harder than hickory, acacia is an extremely hard and durable wood. This hardness makes it resistant to wear and tear, providing exceptional longevity indoors and out. However, the same density and rigidity that make acacia wood perform so well also make it more challenging to mill, cut, shape, join, and finish. With patience and the right tools and techniques, experienced woodworkers can take full advantage of acacia’s hardness to create distinctive, long-lasting furniture, flooring, and other projects that showcase this wood’s unique properties.
