If you are looking for a new type of wood to use around your home for a variety of construction purposes, one type to consider is cottonwood. With that being said, before you get started, there are some things that you need to know about this material, mainly whether or not it is a hardwood, and how strong it is.
There are a variety of factors that we are going to look at today in order to determine how strong this wood really is, especially when compared to other types of lumber.
Is Cottonwood a Hardwood or Softwood?
Cottonwood is an angiosperm or flowering tree, which means that it produces flowers during the summer and then loses its leaves during the winter, which also means that it is deciduous. As you could probably assume, cottonwood is therefore a type of hardwood.
Now, what is interesting to note is that this is technically known as a soft hardwood, as it is actually quite soft, weak, and not very strong in general. In fact, cottonwood is such a soft hardwood that many types of softwood can compete with it, or even outperform it.
Cottonwood Strength: All You Need to Know
First and foremost, there are two different types of this wood that we will be looking at today, which include eastern cottonwood and black cottonwood. To determine exactly how strong any type of wood is, there are five main factors that experts look at.
These factors include compressive strength, bending strength, stiffness, hardness, and density of the wood. These come together to determine exactly how strong, durable, and resilient any piece of wood is. Let’s get to it and figure out just how strong cottonwood is.
Compressive Strength
Let’s take a look at the compressive strength of the two types of cottonwood:
- Eastern Cottonwood – 4,910 lbf per square inch (33.9 MPa)
- Black Cottonwood – 4,500 lbf per square inch (31.0 MPa)
Eastern cottonwood is the stronger of the two in terms of compressive strength. However, in the grand scheme of things, this type of wood is not very strong at all. In fact, even most types of softwood, with the exception of sugar pine, have higher compressive strengths. All types of hardwood also have higher compressive strength than cottonwood. It just doesn’t take very much to compress a piece of this wood.
The compressive strength of wood is also known as the crushing strength. This refers to how much weight a piece of wood can take parallel to its grain. As an easy-to-picture example, imagine a board standing vertically. How much weight could you place on top of the board while it is standing before it snaps sideways and sends the weight plummeting down?
Bending Strength
Let’s take a look at the bending strength of the two types of cottonwood:
- Eastern Cottonwood – 8,500 lbf per square inch (58.6 MPa)
- Black Cottonwood – 8,500 lbf per square inch (58.6 MPa)
As you can see, the bending strength of both types of cottonwood is the same. Once again, when compared to other types of wood, this is extremely low. In fact, most types of softwood have higher bending strength than cottonwood, with the exception of sugar pine. Virtually all types of domestic softwood and hardwood found in North America outperform this material.
The bending strength of wood may also be referred to as the modulus of rupture. The modulus of rupture refers to how much weight a piece of wood can take perpendicular to its grain. This is unlike compressive strength, which measures parallel to the grain.
For example, imagine a board being mounted on a wall so that it is 100% horizontal and not supported from below. Now, imagine a bucket being hung off the end of that board. How much water could you fill into that bucket before the board snaps?
Stiffness
Let’s take a look at the stiffness of the two types of cottonwood:
- Eastern Cottonwood – 1,370,000 lbf per square inch (9.45 GPa)
- Black Cottonwood – 1,270,000 lbf per square inch (8.76 GPa)
Eastern cottonwood is the stiffer of the two types of cottonwood. With that being said, again, this wood in general is not very stiff and it does bend very easily. As is the case with the other categories so far, sugar pine is one of the only types of wood out there that isn’t as stiff as cottonwood. However, the vast majority of domestic North American softwoods and hardwoods are much stiffer than this material.
The stiffness of wood may also be referred to as the modulus of elasticity. This measurement simply refers to how much weight a piece of wood can take in its center before it begins to sag, bend, or lose shape. For instance, imagine a piece of wood spanning across a canyon. How much would you have to weigh to make that board bend in the middle when you walk across it?
Hardness
Let’s take a look at the hardness of the two types of cottonwood:
- Eastern Cottonwood – 430 lbf
- Black Cottonwood – 350 lbf
Eastern cottonwood is the harder of these two types of cottonwood, although both are considered quite soft. Even a sugar pine is harder than black cottonwood, with virtually all types of softwood being harder, which is surprising seeing as cottonwood is technically a hardwood. Moreover, all types of domestic North American hardwood are much harder than this material.
The hardness of wood is one of the factors that many people look at when determining its strength. The reason for this is that the hardness of wood refers to how strong or resilient it is in terms of physical damage like denting and scratching. This is especially important when it comes to something like furniture because you don’t want it to get dented or scratched. This is typically measured on the Janka hardness scale.
Density
Let’s take a look at the density of the two types of cottonwood:
- Eastern Cottonwood – 28 lbs per cubic foot (450 kg per cubic meter)
- Black Cottonwood – 24 lbs per cubic foot (385 kg per cubic meter)
As you can see, eastern cottonwood is the denser of these two varieties. However, in the grand scheme of things, this is still a very lightweight tree.
Even sugar pine is heavier than black cottonwood, with virtually all types of softwood beating it. Of course, all types of hardwood out there are also much heavier than cottonwood.
The density of wood refers to how heavy a piece of wood is in relation to a specific area or size. This is generally measured in either pounds per cubic foot or kilograms per cubic meter.
Is Cottonwood Strong?
Okay, so most people would say that cottonwood is a fairly strong and durable type of wood. However, based on scientific facts, mainly the comparisons made across all five of the factors we looked at above, it serves to reason that cottonwood is actually not very strong at all.
This wood scores very low on all fronts, which is true for compressive strength, bending strength, stiffness, hardness, and density. Although people may call it a hardwood, it is extremely soft, bends easily, and is just not very durable overall.
Summary
Cottonwood looks nice and it works fine for basic uses, but don’t expect it to be structurally sound. This is not something that you would build anything out of that needs to handle a lot of weight or pressure.