Janka Hardness Scale – Definition and Applications
When choosing the kind of wood you’ll use for your new construction or house project, it’s important that you know how hard the wood is. The harder and rarer the wood, the more difficult it will be for you to work with them. However, they will also be more durable.
The most trusted wood hardness scale is Janka Hardness Scale. If you’re looking for wood that you can use in making durable furniture, you can look for wood with 2000-3000 Janka rating. If you are planning to build wooden bridges and ships, you will want to buy wood with at least 3500 Janka rating.
What is Janka hardness scale?
The Janka Hardness Scale was developed by the Austrian wood researcher named Gabriel Janka back in 1906. However, it was only in 1927 when Janka’s scale was standardized by the American Society for Testing and Materials (ASTM). Now, this wood hardness scale is used in determining how hard a particular type of wood is.
The scale was created to show the Janka hardness test results. The test computes the pounds of force (lbf) one requires to drive one 0.444” steel ball into a 2”x2”x6” wood. The higher the force one needs in order to push the ball halfway into the wood, the harder it is.
The wood’s hardness usually varies according to the wood grain’s direction. So, when testing is done on the wood surface that’s perpendicular to the grain, the test usually gives higher results. In other words, a wood species can differ in hardness from its wood family.
This wood hardness scale starts at 0 lbf, the wood closer to which is the softest and most prone to scratches and dents. It is to be noted that there is no type of wood with 0 lbf. The highest Janka rating so far is 5,060 lbf, which is the hardest wood.
Both woods with the lowest and highest rating will not be good options for flooring. Why? The former can easily be destroyed while the latter will be too hard to saw.
Here are the top 10 hardest wood according to the Janka hardness scale:
And here are the top 10 soft wood according to the wood hardness scale:
Application of Janka Hardness Scale
You can refer to the Janka Hardness Scale in a number of situations.
1. When you are choosing flooring for your home
Knowing the Janka scale rating of your prospect lumber will give you an indication of the floor’s hardness. Will it be able to withstand common wear and tear problems? How many years will it last without any need for repair and replacement? Is it easy to maintain? How will it be installed? All these questions can easily be answered when you are aware of the wood’s hardness rating.
2. When looking for highly durable materials
Let’s say that you are tasked to build a wooden bridge for a park. You can’t simply pick the wood you first see. You need to have proof that it will withstand harsher weather conditions and more demanding situations. In which case, you only have to refer to the Janka hardness scale. It will tell you how easily a type of wood will scratch, dent, rot, and wear.
3. When planning your next project
This wood hardness scale can also be used when you want already have the wood, but not quite sure what you’ll do with it. The wood may be an extra piece from your previous project, or a gift from a friend. In which case, the scale will be able to tell you where it’s best to use specific kinds of wood.
4. When buying tools for construction
Tools that work with wood with 600 lbf may not work with wood with 3000 lbf. The harder the wood is, the more difficult it is to cut them. Thus, you will need stronger tools for sawing, planing, routing, sanding, nailing, etc.
5. When planning your budget
It’s true that the Janka hardness scale does not necessarily impact the pricing of the wood. Wood prices depend on how readily available it is. However, you’ll soon notice that the harder the wood is, the rarer it is. Let’s take Australian Buloke, the hardest wood on the scale, for example. The wood is rarely found outside Australia, so not a lot of people can purchase it. Since it’s rare, it’s more expensive than other wood species.
While the Janka hardness scale will tell you how hard the wood is, it does not indicate how strong it is. You can’t use it to determine how soft the wood will feel in terms of comfort. Also, no matter how high the wood is in this wood rating scale, it is not an assurance that it will last long, what matters more is how well you take care of the material.