In this lesson we’ll cover the standard for testing the hardness of wood, one of the more important wood properties. Wood hardness is defined as the resistance of a sample of wood to denting and wear. The most commonly referenced standard is the The Janka hardness test, named after Austrian-born emigrant Gabriel Janka. A common use of Janka hardness ratings is to determine whether a species is suitable for use as flooring, but there are other wood applications where this hardness value is important. The higher the value, the harder the wood.
The test measures the force required to embed an 11.28 millimeters (0.444 in) diameter steel ball halfway into a sample of wood. In the United States, the Janka Hardness test is referenced by the American Society for Testing and Materials (ASTM) standard D1037.50 (ASTM.D1037.50). This video demonstrates how this test is conducted.
This Video Duration – 1:18 Minutes
The Janka hardness test results hardness numbers are an average. There is a standard deviation associated with each species, but these values are typically not given for commercial work. Numerous factors associated with tree growth means that the Janka Hardness value can vary from one piece of lumber to another even if the lumber is of the same species of wood. The Janka hardness in North America is typically represented by a number representing newton pounds forces, and woods are shown on a comparative scale.
Example Janka hardness Chart