balsa wood

Balsa Cracks

Balsa starts to crack shortly after being cut down. The trees are filled with water and are very heavy. The water leaves the ends first leaving a difference in density and water content causing the balsa to change shape and crack starting from the ends. If not kiln dried the whole trunk will crack. The faster the balsa is kiln dried the less cracks will be present. The blocks are placed in a huge oven (often powered by the balsa scraps from cutting the blocks square) and are dried for several weeks. The temperature is kept constant while the blocks bake. Once finished the blocks are no longer in danger of cracking. The ends are cut off past the initial cracks and the blocks are cut to length.

One other type of cracking can occur if one side of a block is drastically denser than the other. This usually happens when one side is about 6# or less balsa and the other side is much heavier. There is a tug of war and the lighter side looses. This type of crack will go horizontally instead of vertically with the grain since the lighter side failed in tension. Once this happens most of the block is lost for scrap wood.