What is the density of hardwood

Hardwood, softwood and the density of the kiln

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How dense is wood?

The density, also known as the specific weight, is a physical quantity that indicates the mass (kg) per volume (m³) of a substance.

In a very practical way, you need the density to assess the quality of the firewood: If you have firewood delivered that is heavier than usual, this is, for example, an indication of a higher moisture value and thus a lower calorific value.


True density

A chemist would say: "Wood has a true density of 1,500 kg / m³. "
The true density is an ideal size, in which wood is "pulped" into very small pieces and no longer contains any pores or trapped water. The density of this "chemical" wood is almost the same for all tree species. However, when buying firewood, it is seldom delivered "pulped". Therefore, the real density is insignificant in real life.


Bulk density

For real life, however, the so-called "bulk density" is more important, as it provides information about many wood properties such as heat or sound insulation properties, but also about the water content.

Because the gross density describes the density of the wood in its natural state - including the bound substances such as water and air pockets. It depends on the tree species. For example, oak or beech wood has a higher density than spruce or pine with the same residual moisture. With the same residual moisture, the following rule of thumb applies to native wood: the heavier the wood, the more calorific value it has.

However, the water content is also decisive for the density: wet oak or beech is heavier (denser) than dry. Since water at normal air pressure and normal temperature has a density of approximately 1,000 kg / m³, the more water it contains, the closer wood comes to this value.

But there is also wood that is heavier than water. So-called ironwood - that is particularly dense, mostly tropical wood - would not float on water at about 1,200 kg / m³ but would go under because it is too heavy (too dense).

On the other hand, there is particularly light wood, such as balsa, which weighs only a tenth of that and is therefore used in the past for building rafts and today it is often used in model aircraft.

The calorific value of balsa, on the other hand, is very low, you would need a multiple amount of wood to generate the same amount of heat.


Dose density

When wood is dried to such an extent that it absolutely no longer contains any water, it is called “drying-dry” wood.

A "kiln" has been a device since the Neolithic Age, e.g. to dry grain under the influence of heat. The word comes from Old High German and denotes the opposite of "green".


Hardwood and softwood

Occasionally, wood is divided into the two categories "hardwood" and "softwood". Historically, hardwood means wood that has a kiln density of over 550 kg / m³, such as oak or red beech. Softwood, on the other hand, is wood with a kiln density below 550 kg / m³, e.g. poplar, willow or linden.

According to this strict interpretation, chestnut could belong to the hardwoods as well as to the softwoods.

In English one sometimes speaks of “softwood” and “hardwood”. This can mean softwood and hardwood, but also softwood and hardwood.