What is the Density of Wood?
Have you ever wondered what type of wood goes with your woodworking project? They say that there is a type of wood for a specific project and the ideal wood is based on the wood’s density or the density of wood.
Basically, all the other quality follows after you have a clear idea of how dense the wood you would like to use. This article will help you understand what the ideal density is and how this value applies to different woodworking projects.
What is density anyway?
Density is defined as the mass found in a unit volume (of the material. Density can be measured at the same moisture content. You must understand that wood is a hygroscopic material which means that this has the natural property to attract and retain moisture.
When moisture is absorbed by the wood, the process is called adsorption. This increases weight and volume of wood. The volume of wood increases when it is below the saturation point (about 30 % moisture). Also, basic density is the oven-dry weight of wood.
Why does wood behave this way? It is because wood is mostly made of dead cells, which are made of cell walls and cell cavities. The density of the material that makes up the cell walls is nearly constant, about 1.5 g.cm-3 for temperate wood.
Therefore, there is no specific value for the density of wood. This varies depending on the amount of material or the cell wall and voids cell cavities found in the volume of the material.
Aside from the amount of cell wall and voids in the material, the density of wood is also affected by the basic structure of wood. For instance, latewood or wood that has been produced in the later part of the growing season have thicker walls from cells that have thicker walls and smaller cavities. Earlywood or wood made during the early part of the growing season have thinner walls.
Therefore, latewood is denser compared to earlywood and explains why the density of wood increases with increasing proportion of latewood. In the case of ring-porous hardwoods, the increase of tree-ring width is associated with the increase of latewood proportion as well as density. When it comes to softwoods, the proportion of latewood decrease with increasing ring width.
Wood extractives can affect the density of wood
Extractives or wood extracts are molecules that are extracted from wood with the use of solvents or other methods. The most common extractives are waxes, resin acids, fatty acids, and terpenes. These are phenolic, alicyclic or aliphatic compounds. The presence of these compounds affects the density of wood.
For example, higher amounts of extractives bring about the higher density of heartwood compared to other types of wood with very little extractives like sapwood. When extractives are removed, the density of wood reduces.
How is the wood density measured?
Density can be measured by measuring mass (weight) and volume. Oven-dry mass is measured by placing the chosen of wood in an oven at 103±2°C. Wood is “baked” until its weight becomes a constant. The volume of wood is determined by measuring the dimensions of wood or by using water displacement or the Archimedes principle.
You can find out wood density by measuring the mass and volume. Using the Imperial system of measurements used in the United States, density is measured in units of pounds per cubic feet. Because weight and mass are related by gravity, this specific weight measurement is considered a measure of density.
So to measure density, weigh your piece of wood in units of pounds. You can use a block or a cylindrical piece of wood such as a section of the trunk. Use a weighing scale which can be an analog or a digital scale. Measure the length, width, and height of a block of wood. This is measured in feet.
Multiply the length by width by height for rectangular pieces. Calculate the volume of a cylinder by dividing the diameter by two to calculate the radius. Square the radius and multiply the result by the value of pi or 3.14 and then multiply the answer by the length. Divide the weight by the volume to get the specific weight or Imperial density.
The density of wood is an important factor in determining the strength and the versatility of wood. Basically, the denser the wood, the stronger it is. Strong wood is ideal for building projects that need to be durable and can stand the test of time.