Wood is an extremely common building material and is also used widely for crafts, art and other projects. One of the first things you’ll notice when you begin working with wood is the sheer variety of possible woods to work with. There are thousands of different species of trees whose wood is used in various forms. Wood species vary in many ways, but a key factor in finishing wood is the hardness of the wood. A common measurement for wood hardness is the Janka scale.
The Janka scale measures the resistance of a sample of wood to denting and wear and is typically expressed in lbf (pounds-force) or N (Newtons). The US typically will use lbf. This hardness is important in finishing as it is usually a good idea of how porous the wood may be. Very soft woods are usually also very porous and will sometimes require more product to fully seal the surface. The more porous the species, the more product is absorbed INTO the surface and less is forming the continuous waterproof layer OVER the wood surface. There are a lot of books, websites, articles and other sources of information that may show varying Janka numbers for the same species, but they are usually in the same general range. Specific Janka numbers are not necessarily important, but knowing where something falls on the list will help with your wood project (white oak and red oak can be treated the same, for example). In regards to applying a finish to wood, you are usually most concerned about really soft woods and then everything else.
Harder Woods and Softer Woods
The term hardwood can be quite deceiving as many people use the term to describe surface made of wood. As you’ll see in the table below, pine and douglas fir woods are very soft, but a floor made from them is still usually referred to as a hardwood floor. In general, many people would consider wood species that are softer than red oak (1,290 lbf) to be on the softer side and anything red oak or harder would be considered a harder wood. Many people will also classify hardwoods as anything from trees that lose their leaves in the fall (deciduous trees) and soft woods from conifers or evergreens (think pine and fir). This isn’t 100% black and white, but it is usually true.
There are a few ways to identify wood as hard or soft without knowing exactly what it is. Usually, the easiest way is to check the weight of the wood. Soft woods are usually very light and harder woods are quite dense and heavy. Most lumber at your big hardware stores will be untreated pine for framing walls and other construction. Pick up one an untreated 2×4 to see how heavy a piece of soft wood feels. Compare that to some of the specialty lumber and see where those fall on the Janka scale to get a general feel for the weight vs. hardness.
Common Wood Species
Dimensional wood (solid boards, planks, etc. of wood) is derived from trees and trees are usually regionally specific. Trees that are harvested locally are usually lower in price and are more readily available which means that certain woods may be more common to your particular region. A list of commonly used woods in construction and their Janka scale ratings (in lbf) are shown below1.
|Wood||Janka Scale Rating|
|Hard/Sugar Maple||1,450 lbf|
|White Oak||1,360 lbf|
|American Beech||1,300 lbf|
|Red Oak||1,290 lbf|
|Yellow Birch||1,260 lbf|
|Heart Pine||1,225 lbf|
|Black Walnut||1,010 lbf|
|Paper Birch||910 lbf|
|Eastern Red Cedar||900 lbf|
|Southern Yellow Pine||870 lbf|
|Douglas Fir||660 lbf|
|Yellow Poplar||540 lbf|
|Eastern White Pine||380 lbf|
Names of Wood Species and Confusion
As mentioned earlier, there are thousands of wood species that are used throughout the world. The naming conventions used for all of these species can become very confusing. It is important to look at the exact species (if possible) to avoid confusion. If you search for Janka lists, you’ll probably noticed that some words are repeated many times on that table. You’ll most likely see numerous versions of maple, mahogany, walnut, cherry, oak and others. Many times, the same species of wood may have multiple names. This is usually an attempt to describe the appearance of the wood and to compare exotic woods to more well-known varieties. A good example of this is with Ipe (pronounced EEE-pay), which is also regularly referred to as Brazilian Walnut. As you can tell from the list above, Ipe and black walnut have very different Janka ratings (3,684 lbf vs. 1,010 lbf respectively) and are actually very different. If you have black walnut (much more common) and just stopped looking after the first instance of Walnut, you would think you have incredibly dense wood when in fact, black walnut is actually relatively soft. Mahogany can be particularly confusing because there are many varieties and many of them are common.
If you are unsure, it is best to ask the supplier if possible. If you are refinishing an old piece you can usually ask a local lumber yard or other professional which species would be common for a given time period for your region. Also, it is usually safe to assume the standard common version (i.e. American cherry) instead of the more exotic version (i.e. Jatoba, a.k.a. Brazilian Cherry) unless its explicitly stated.
Wood is a natural occurring substance, so there will always be variation, but the Janka scale is usually pretty accurate. There are always exceptions to the rules of course and there are a few that you may encounter more than others.
Reclaimed wood is becoming more popular. Reclaimed wood may behave very similarly to virgin wood, but it may be more absorbent. Reclaimed wood commonly has more “defects”, such as knots, nail holes, insect holes, dents, dings, cracks, etc. and it also may be more weathered and “dried out”. This may cause the reclaimed wood to absorb finish more readily than virgin wood.
This is a very complex subject and more can be read in our End Grain and Waterlox guide, but essentially, there is more than one way to cut a tree. Boards are three dimensional objects and you may encounter all six faces of the wood surface on some projects (small crafts), where others you may only be coating one side (like a floor). Most coating will usually be done on the face (or flat, plain) grain or edge grain. These are the longer sides of the boards and there is not much difference when it comes to finishing these sides. The ends of the boards, however, can behave quite differently. This is called end-grain and it is extremely absorbent.
Spalted, Burl, Rotten, punky, etc.
There are certain circumstances that will alter the normal structure of the wood. Some common terms would be rot, burl, punky or spalted. Usually this means some form of degradation or loss of integrity of the wood’s normal structure. Usually this makes the wood softer or more porous and it may accept stain or finish differently.
1 All numbers from https://en.wikipedia.org/wiki/Janka_hardness_test – As of June, 2019