I am constantly asked whether balsa is better than basswood. Here are some of my notes comparing the two woods.
Balsa is cheaper and more available than basswood. This means you can buy more wood, and build more bridges for the same amount of money. By building more, you will gain valuable experience and improve your skills. When it is all said and done, you may be able to build a better balsa bridge.
Balsa is stiff, while basswood will bend.That’s right, you can bend basswood more than balsa. That is good if you are building an arch bridge. But what if you don’t want your bridge to bend? Balsa will give you a stiffer piece than basswood for the same size. However, I have seen balsa bend a lot under heavy load without breaking. I am not sure why it was able to bend so much, but it did.
You can get more cross-section for the same mass with balsa. In other words, you can have a bigger piece of balsa for the same weight of basswood. In compression members, larger and lighter pieces will actually hold more than smaller, heavier ones.
Basswood won’t rip off at the joints as much as balsa. Sometimes the face grain of balsa will tear away at the joint. Basically, basswood holds itself together better than balsa.
Balsa comes in a wide range of densities. You don’t always know how strong the wood is that you are getting. Basswood usually comes in a much smaller range, which means you can be more consistent with basswood. That problem can be fixed if you weigh each piece of wood before gluing it to the bridge. That way, you know exactly what is going on your bridge and can keep accurate records.
Balsa is less likely to be the same strength throughout its entire length. If you buy a piece 24 inches long, it may be stronger at one end then the other. This just complicates things, making it harder for you. Basswood is usually uniform in strength.
Balsa will sand easier, but basswood won’t crush.You can squeeze a piece of balsa, and totally deform it. A “squeezed” piece of balsa is weaker, because the internal atomic structure is messed up. You need to be more careful when working with balsa.
Balsa changes weight with changes in humidity more than basswood. Many times I have had a balsa bridge lose weight after setting it in the sun for a couple of hours. Of course, the opposite is true. Balsa bridges will gain weight after humid days. Basswood does not change so much with the weather.
For the same mass, basswood pieces must be smaller. Usually, this means that a basswood joint will have less surface area for glue than a balsa joint. That means you may have to use stronger glue with bass, which might add weight.
So you see, there are many factors that play into which wood is better. Basswood may be better in some places, and balsa in others. I encourage you to experiment with both woods. Specialized Balsa is the company I recommend for buying balsa.
Don’t forget about the other woods.
Birch, Spruce, Aspen, Pine, and others are all alternatives to balsa and basswood. But I guarantee that you won’t be able to find them like you can balsa. They will cost more money. But don’t immediately rule them out, you may want to play around with them, and check out their qualities. Let me know what you find out.