Scott Leavengood of OSU is back with more on Wood Hardness! I’m just going to turn this post right over to him to address a question received a few months back on “Monnin hardness” testing. However, first I do want to say that it sounds like the wood flooring industry needs to look into creating a meaningful test (or tests) specific to our industry. And that test should also reflect the various forms our product takes—solid, engineered with various cores and face veneer thicknesses, and of course, the type of finish we might apply… anyone have any suggestions? Feel free to post ideas.
In the meantime, Scott, the floor (so to speak) is yours:
We received a great question from a reader about Monnin hardness. As the reader said, don’t the Brinell or Monnin hardness tests “…better replicate the abuse a floor takes from a high heel shoe”? Further, consumers want to know “…what damage is caused by constant pressure by the heel on the floor, not how much force is needed to cause a really bad dent.”
First, let’s talk about Monnin hardness. I must admit that I’d never heard of this test method. So I did a little research to learn more about it. Chapter 9 of the book In Situ Assessment of Structural Timber, describes several hardness tests, including the Monnin test. This test is similar to the other hardness tests except a larger ball (a cylinder, in fact) is used. You might recall the Brinnell and Janka tests involved embedding a ball of 10 to a little over 11 mm into wood. With Monnin hardness, the test involves embedding a 30-mm cylinder with a maximum load of 2 kN (about 450 lbs.) over a period of 5 seconds. The figure below shows the test apparatus.
Since it’s hard to measure the depth of the penetration (t), the width of the indentation (l) is measured instead and depth calculated from that. Monnin hardness is 1 over the depth of penetration.
And maybe you’re thinking now what I thought when I read about this test method – it sounds a bit challenging to accurately measure the width too! That’s actually what the authors of the book chapter say – “Because it is not easy to measure accurately the width of the impression, the Monnin hardness is subject to greater experimental error than in the Janka test.” Looking back at part 4 of this series, you might recall that the same situation exists for the Brinell test – measuring hardness with the Brinell test requires measuring the depth of penetration. This is really tough to do accurately!
So there’s the bottom line really. As the reader said, consumers want to know what damage is caused by constant pressure on a floor, such as by a heel vs. how much force is needed to cause the floor to dent (i.e., Janka hardness). And the Brinell and Monnin tests do seem to provide a better measure of hardness measured in terms of damage caused by constant pressure. So why is it then that most measures of hardness we see reported are from the Janka test vs. the other test methods? Well it seems the answer is due to 2 primary reasons – Janka hardness involves less experimental error and it’s an easier test to conduct.
In conclusion, we should mention that the test we now know as Janka has been modified from the original. Gabriel Janka’s test was originally developed as a modified Brinell hardness test; he expressed the results as the load divided by the projected area of contact. However the ASTM test has always reported the results as the load at a penetration of 0.222 inches (i.e., half the depth of the ball).
Riggio, M., and M. Piazza. 2010. Chapter 9: Hardness Test. In: In Situ Assessment of Structural Timber. B. Kasal and T. Tanner (eds.).
Doyle, J. and J.C.F. Walker. 1985. Indentation Hardness of Wood. Wood and Fiber Science 17(3): 369-376.
Elizabeth Baldwin is Environmental Compliance Officer for Metropolitan Hardwood Floors. In her 25 plus year career in the wood industry has visited over 70 countries and hundreds of facilities of all sizes and types. She describes herself as a “jack of all wood trades.” Familiar with jungles of all sorts–having camped out along the Amazon and walked the halls of Congress–she blogs for the NWFA on both environmental and regulatory issues for educational and informational purposes only. Her blog is not intended and should not be construed as legal advice. Persons seeking legal advice on compliance with CARB, TSCA, the U.S. Lacey Act or any other law, regulation, or compliance requirement/claim should consult with the regulatory agency directly and/or a qualified legal professional.