What is a Janka Hardness Rating and How Important is it?November 9, 2018
A Janka rating is a hardness estimate given to wood. In hardwood flooring, the score is used to determine the durability of hardwood species that it might be suitable for a home. No matter what species you’re interested in, chances are, it has already undergone the Janka hardness test. Use this guide to understand precisely what each rating means for a better likelihood of choosing the right hardwood flooring.
First, Who Created the Janka Rating?
The Janka system is named after an Austrian man named Gabriel Janka who worked for the Forest Products Lab of the U.S. Department of Agriculture (USDA). Tasked by the Department with scientifically measuring the hardness for U.S. hardwoods, he developed the wood rating scale now used around the world. The American Society has since formalized the Janka hardness test for Testing and Materials (ASTM).
Similar indentation hardness tests are used throughout engineering to discover the hardness of various materials. By understanding the hardness, manufacturers know how much wear and tear different materials can take, which applications to use them in, and can thus create high-quality tools, building materials, and other products.
Next, How is the Janka Hardness Test Done?
The Janka hardness test was designed to measure the resistance of a sample of wood to denting and wear. The method is now standardized and anyone can duplicate it in the case that new species need to be analyzed. Not that you’ll have to perform this test yourself, but here’s a summary of how it works:
- A sample plank of solid, unfinished, knot-free wood with a moisture content of around 12% is placed on the ground.
- An 11.28 mm steel ball is placed on top of the wood sample.
- Precisely-measured force (in lbs) is then placed on the ball until it is embedded halfway into the wood sample; this leaves a 200 sq mm hemispherical indentation on the plank.
- The process is repeated because two areas on the face of each specimen must be tested.
- All of the collected data is recorded and averaged.
A species’ Janka rating is a measurement of the amount of force (usually in pounds of force, or LbF) required to create the 200 sq mm indentation on the surface. There is a standard deviation associated with each species. In a nutshell, the more pressure a wood species can take, the higher it’s Janka rating. Softer woods will require less pressure to create an indentation than harder woods.
Then, What is a Good Janka Rating for Wood Floors?
For flooring, one of the most important criteria in choosing the right wood is its resistance to denting as a result of pressure from, say, a stiletto heel, the tip of a small chair leg, a pet’s toenail, etc. The Janka hardness test, to some degree, replicates such.
Important to note is the fact that during the Janka hardness test, specimens contain about 12% moisture. Wood flooring, however, has been milled at about 6-9% moisture content and, by the time you walk on it, has been treated with several layers of protective finish. Furthermore, with engineered wood flooring, different materials exist underneath the top hardwood layer — these layers significantly affect the floor’s overall hardness. So, there is a variation between the Janka rating and the final hardness of any hardwood flooring.
With that said, as a general rule of thumb, wood species used in flooring should generally have a Janka rating of 1,000 or higher; this isn’t to say that wood species with a Janka rating in the hundreds will not work. Lower ratings do indicate that the wood is softer and more prone to damage from furniture, foot traffic, and pets.
Now, Look at a Hardness Chart Showcasing Some of the Most Common Hardwood Flooring Species
In reality, all flooring is subject to damage and wear. In the end, the primary factor in how well your wood floors hold up over the years is how you treat and care for them. While it is advisable to start with a harder wood if you anticipate high traffic and rough use, Janka rating is not the only factor to consider. You should keep your floors clean, protect them with rugs in high-traffic areas, and choose woods and finishes more likely to mask scratches and dents; this can be just as, if not more important. Still, this chart can be used to help you make a species choice based on hardness.
The above chart showcases the typical Janka side hardness for some of the wood species commonly used in flooring. Some woods like Snakewood have Janka ratings of nearly 4,000 LbF, which is too hard to comfortably cut and otherwise work with when installing floors using traditional methods. Other species are as low on the scale as Balsa at 70 LbF; this, in its raw form, is too soft to withstand typical foot traffic in a home. But, in home decor, the only time you’ll see black and whites is if you’re an Ansel Adams fan.
While the Janka hardness test and rating scale are an excellent way to determine what wood species might work for the floors in your home, it’s not everything. You will need to take other matters into account such as how the Sun will affect the color of your floors over time, what type of finish you want to use, and the aesthetic appeal of various wood grains. Come back often to learn more about hardwood flooring.
If you have questions about the hardness of a species not listed here, contact a hardwood flooring expert who can answer your questions in detail.
This post was originally published on the Macwoods blog on March 29, 2014, and has since been updated for clarity.