Have you ever wondered why woods like Ebony sink while others like Balso float on the water? If so, stick around to find out.
Objects float according to their density
To begin with, we must understand what is the density of an object and how it affects its buoyancy. You can read the article on basic concepts of wood to learn more about density or any topic related to this material.
So, density is the relationship between the weight or mass of an object (or substance) and the volume that the object occupies. This ratio is measured in kilograms/cubic centimeters (kg/cm3) for solid objects.
Density in wood
The density of wood is very variable because many factors determine how dense (heavy) or light it is.
So, we can see that wood density depends for example on its species, because if we talk about a slow-growing wood such as the African Granadillo (Dalbergia melanoxylon), we see that its density is high or very high, 1270 kg/m3 to be exact.
This can be explained by the fact that the tree has had several decades or even centuries to grow and therefore has been able to produce a very dense (compact) wood.
On the contrary, a fast-growing species such as Kiri wood (Paulownia Tomentosa) will have a very light wood, 280 kg/m3 approximately.
In the following image, you can see the range of densities in which woods are classified; it will serve as a reference to determine if a wood is more or less dense.
Now that you know these values, you need to know that density can vary greatly among trees of the same species. For example, you are unlikely to find a tree whose trunk has only one density measurement.
That is, some parts of the wood will be denser than others and this may be due to the concentration of water in the wood at the time of measurement.
Likewise, it is logical to think that the denser the wood is, the harder and more resistant it must be, right?
Well, if you think so then you are partially right, in most cases, the densest wood species are also the hardest and most resistant.
However, the rules have exceptions as in the case of Quebracho, the hardest wood on the planet and one of the densest too, but not the densest.
In addition, many consider teak wood to be the most resistant or durable wood, and yet it is half as dense as Quebracho and about 4 times less hard, but more resistant than it.
The above serves to make you understand that, although hardness, density and durability of wood go hand in hand, they are not always equal or equivalent.
Why does wood float?
It is often said that wood floats on water, and that is true. However, this claim is incomplete alone.
Because wood floats, yes, but only when its density is lower than the density of the liquid in which it is found.
In other words, if the wood is denser than the liquid it is in, it will sink.
So, since most wood has a lower density than water, it is said that wood always floats. But some wood is denser than water and that is why it doesn’t float in it.
But, anyway, even if you have a dry piece of wood remember that wood has the tendency to absorb or expel moisture depending on the environment.
Therefore, if the wood gets wet, it gets water saturated and expels air (which is less dense than water), so it increases in weight and becomes denser. For this reason, it can overcome the density of water and sink.
Note: remember that wood doesn’t sink because it weighs more than water but because it is denser than water.
Is the density of water always the same?
We have talked a lot about wood sinking if it is denser than water, but what is the density of water?
The answer is: it depends.
Pure or distilled water has a density of 1 when it is at 4ºC. However, its mass increases when ions are added to water.
This is important because it means that the buoyancy of wood can change according to the purity of the water, i.e. if it is dirty or polluted water it can be denser.
In addition, it happens that the density of the water depends on its temperature, because the colder it is, the denser it will be and, on the contrary, the warmer the water is, the lower its density will be.
And what does it mean that the density of water is equal to 1?
The fact that the density of water is equal to 1 g/cm3 implies that 1 kg of wood is equal to 1 liter of water, that is, the volume of water is perfectly equivalent to its mass.
Also, water is a very stable substance and therefore its density does not usually vary much unless the temperature changes.
| Temperature | Water density |
| 4 ºC | 1000kg/m3 |
| 20 ºC (Ambient temperature) | 998 kg/m3 |
| 100 ºC | 958,05 kg/m3 |
Therefore, the density of water at room temperature is 998 kg/m3 and that is the value that you must take into account to measure the buoyancy of objects.
Therefore, if the wood has a density of less than 998 kg/m3 at room temperature, it will float; if not, it will sink.
Which woods do not float in water?
Here are some woods that exceed the density of water and therefore do not float.
5. Gabon Ebony Wood
This tropical wood native to Africa is one of the finest in the world and is very desirable for its high quality.
It has a very particular and attractive appearance, as it is very dark (almost black). It is also very resistant.
It has a density of: 1050 kg/m3 and is therefore a very heavy wood.
4. Vera wood
Native wood from the Americas, it is widely used for lathe work.
This wood is very heavy since it has a density of 1192 kg/m3.
Lead tree wood
This African species is difficult to obtain outside its natural habitat. It is very strong and dense; it has a density of 1215 kg/m3.
3. Lead tree wood
This African species is difficult to obtain outside its natural habitat. It is very resistant and dense; it has a 1215 kg/m3 density.
2. Quebracho wood
This South American species is the hardest on the planet and is threatened by overexploitation.
It has a density of 1235 kg/m3.
1. Ironwood
Originally from the Caribbean, ironwood is the densest wood on record with a density of 1355 kg/m3.
However, if you want more examples of woods that don’t float, visit the article on the heaviest woods on the planet, all of which have a density greater than that of water.
Also, maybe you noticed it or maybe you didn’t, but what all the woods we just mentioned have in common is that they are tropical woods, as high densities are very common in those species (because they are mostly slow-growing).
So you know, the buoyancy of the wood depends on its density, although more factors come into play.