All the timber sold for flooring is quality hardwood, capable of withstanding normal foot traffic for many years. In order to suitable for flooring the species of timber must rank high on the Janka hardness scale.
Then Janka hardness test looks at the force required to press an 11.28mm Steel ball into the surface of a piece of wood. The force required to press the ball 5.6 mm (half its diameter) into the wood is the Janka rating.
In Australia the Janka rating is usually given in kilo Newtons (kN). A timber rating of 6kN to 10kN is considered quite satisfactory and reliable for timber flooring. Some less common species of timber have Janka ratings of up to 16kN.
The Janka rating does measure the hardness of wood, and is a good indication of its durability and resistance to damage. But this is different to the strength and bendability of wood. It is possible for some wood to have a hard surface yet be prone to flexing under some conditions. Timber sold for hardwood flooring will have a fairly high strength rating as well as a reasonably high Janka hardness rating.
Some harder woods are preferable for outdoor decking and other garden structures.
• Jarrah 8.5kN Janka
• Blackbutt 9.1kN
• Spotted Gum 11kN
• Merbau (Asian wood) 8.56kN
• Stringybark 8.1kN
• Sydney Blue Gum 9.0kN
• Turpentine 12.0kN
• Ironbark 14kN The hardest and most durable option.
The Janka test does not apply to other flooring materials like bamboo. Older style bamboo flooring had a high Janka rating but was prone to superficial surface scratching. More modern bamboo flooring is grown for longer and processed differently, given a more durable surface.
All modern timber flooring will be sufficiently hard, able to withstand normal conditions in most homes. It can be re-sanded to give a new surface if required.