Today balsa wood is overwhelmingly used in model aircraft building
and in architectural/engineering models of many sorts. In fact it
is used in any type of model building where it is important to have
a wood that is light and/or easily cut and shaped with hand tools....
in the classroom and the office.
Historically, Balsa wood has been used in
many applications that required high levels of floatation, life-saving
equipment, floats, rafts etc. as well as insulation and in sound
Balsa Tree: Ochroma pyramidale species
Balsa is somewhat like what we would consider our poplar trees here
in Northern Ontario. It grows like a weed tree. Any time there is
an opening in the forest floor, multiple seedlings will shoot up
rapidly, often 12' tall in six months and can reach 15-40" in diameter
in ten years. The strongest tree will eventually dominate an area,
killing off the smaller, remaining trees. As the trees age the center
core rots and the new wood grows more densely. When the tree is
very young the leaves can be as large as 45" across, but as the
tree ages the leaves grow much smaller, in the under 12" category.
Trees are found widely distributed throughout the tropical forests
of S. America, from southern Mexico to Brazil and Bolivia. Ecquador
is the primary source of commercial Balsa exports.
Balsa is a pale white to gray, nondescript wood, with little grain
pattern. It has a distinct velvety feel. It is never bought for
its appearance, but rather its exceptional strength to weight characteristics.
It is the lightest and softest wood on the commercial market, although
not the lightest wood in the world. With a microscope, you would
see that the cells are very large and porous, with limited amounts
of lignin (the glue that holds wood together) between the cell walls.
Balsa's weight is the issue for many balsa purchasers. Its weight
can vary from 4 lbs. Per cu.ft. to 20 lbs. Per cu ft., although
more typically in the range of 6-14 lbs. It strength is directly
related to its weight. Wood that is 6 lbs or less is considered
to be of "contest grade" for any of you who are into model airplane
construction, and used for low stress components. The heavier stock
is for structural components that take more stress. For this reason,
many of the larger distributors, always sort and sell Balsa in different
weight categories. In the green, Balsa has approximately five times
more water, than actual wood, much like our northern white pine.
Balsa finishes easily with standard water based paints, or varnishes.
May fuzz after first coat and require fine sanding.
Most cutting and shaping of Balsa is done with very simple hand
tools, sanding blocks and X-acto blades. Rarely are power tools
necessary unless you are cutting down larger blocks.