Hardwood is the collective term for tropical timber species that are naturally very dense and hard, allowing them to be used outdoors without chemical treatment. Anyone asking what is hardwood exactly should think of species such as Okan, Azobe, Cumaru and Tali — timber that naturally falls in durability class 1 to 1-2 and withstands permanent ground and water contact. That makes hardwood the first choice for structures that need to last for decades without maintenance, such as sheet piling, dam walls, posts in the ground and decking.
Where softwoods like Douglas and larch need treatment or elevation to survive outdoors, hardwood offers that protection naturally. Houthandel Jan Sok in Meppel has supplied TLV-certified hardwood to private customers, sole traders and contractors from the same range since 2009 (KvK 04062841, average 4.8 stars from 141+ reviews).
Definition
In practice, hardwood refers to tropical broadleaved species with high density mass and a natural resistance to fungi, insects and moisture. Under the European standard (EN 350), the relevant species fall in durability class 1 (very durable, >25 years) or 1-2. This means the timber functions outdoors for long periods without impregnation or treatment, even in direct contact with ground or water (use class EN 335, GK4).
Species and durability class
Not all hardwood is the same. At Houthandel Jan Sok we distinguish four species, each with its own application:
- Okan — class 1, permanent ground contact. Fine-sawn and extremely strong; ideal for posts, beams and structures in the ground.
- Azobe — class 1, permanent water contact. Heavy and hard; the standard for sheet piling and dam walls in water, with a lifespan of 30+ years.
- Cumaru — class 1-2, 25-40 years. Warm golden brown (Brazilian teak), harder and more luxurious than Douglas; popular for decking and terraces.
- Tali — class 1-2, permanent ground contact. Versatile hardwood for decking and outdoor structures.
Compare species directly in our articles on Okan vs Tali for decking and the decking material comparison.
Applications
Hardwood is used where long lifespan and load-bearing strength come together: posts for fences and pergolas, beams for load-bearing structures, planks for cladding and fencing, decking and terrace planks, and sheet piling and dam wall structures in water. For decking the lifespan is 25-40 years; for Azobe sheet piling 30+ years, even permanently under water.
Pros and cons
Pros: natural durability without treatment, very long lifespan (25+ years), resistant to ground and water, high structural strength.
Cons: higher price than softwood, heavier and therefore harder to work, and untreated timber greys over time (cosmetic, the structure is not affected). To delay greying, oil or stain can be considered.
Curious how hardwood compares to a cheaper alternative? Read our comparison hardwood vs Douglas.
Maintenance
Untreated hardwood greys naturally to a silver-grey colour. That is purely cosmetic and does not affect the structural properties. To keep the original colour, choose a suitable hardwood oil or stain and repeat annually. Beyond that, an annual cleaning to remove algae and dirt is sufficient. Hardwood can then be used for years with low maintenance — one of the reasons it is preferred for sheet piling and dam walls.
Frequently asked questions
What exactly is hardwood?
Hardwood is the collective term for tropical timber species — such as Okan, Azobe, Cumaru and Tali — that are naturally very dense and durable and can be used outdoors without chemical treatment, even in permanent ground or water contact.
How long does hardwood last?
The lifespan depends on the species and application: decking planks 25-40 years, Azobe sheet piling in water 30+ years, and load-bearing structures with Okan 25 years or more, thanks to durability class 1 to 1-2.
Does hardwood need treatment?
No, hardwood is naturally durable and does not need impregnation or preservation. Oil or stain is optional and only meant to preserve the natural colour; without treatment the timber greys cosmetically.
Which hardwood species do you supply?
Houthandel Jan Sok supplies TLV-certified Okan, Azobe, Cumaru and Tali, fine-sawn, as posts, beams, planks, decking and sheet piling. See the hardwood range for directly available sizes.