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BALSA
FAMILY
NAMES
Ocrhoma lagopus
also Ochroma pyramidale of the family Bombacaeae.
OTHER NAMES
Balsa, corkwood,
guano, lanero, polka, top, tami.
HEIGHT/WEIGHT
Average height
is 60 to 70 feet. Average weight for commercial timber is 6 to 11
pounds per cubic foot but wood can weigh as little as 3 pounds per
cubic foot and as much as 20 pounds per cubic foot, seasoned.
PROPERTIES
Balsa must be dried soon after it is felled to avoid fungal
discoloration and decay. Kiln drying over air drying is recommended
by experts to protect from splitting and warping of the material.
Once seasoned, the wood is stable in service. Wood is easily worked
but experts recommend using very sharp and thin-edged tools. Balsa
takes screws or nails easily, but they will not hold; gluing is the
recommended means for joining. Wood is not suitable for solid
bending as bending the wood will cause buckling. Balsa is used as
bent members in composite construction. It can be stained but
absorbs materials during the process. Wood is perishable and
susceptible to insect attack, but can be treated with preservatives. |
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Balsa
is considered a lightweight among woods. While it is the lightest of the
commercial hardwoods and unlikely to make anyone’s top-10 list of fine
cabinet woods, balsa has a long, proud history — it was used in
construction of the Allies’ planes in World War II — and is one of the
most frequently imported woods to the United States. In World War I, balsa
was used extensively in making life rafts and for packing armor plates for
battleships. Because of its light weight and good insulating properties,
it is still used as a packing material for highly finished materials.
Grows
Fast, Dies Young
Balsa
(Ochroma lagopus) grows in the West Indies, Central America and
tropical South America. Ecuador contributes large supplies of balsa, as do
the plantations of India, Indonesia and the Caribbean.
According
to Albert Constantine in the book Know Your Woods, under favorable
circumstances, balsa trees are ready for cutting when they are seven years
old. The trees begin to deteriorate at 12 to 15 years of age. “Older
trees often develop rot at the base and become worthless,” Constantine
adds.
Most
of the balsa that is sold is the sapwood, which is white, off-white or
oatmeal colored, sometimes with a light yellow or pink cast. The heartwood
is pale brown.
Balsa’s
strength varies, say the editors of the book World Timbers, with its
density. “Where strength is important, material should be selected on a
density basis with reference to published strength figures. As a rough
guide, commercial balsa of average density has from one-half to one-third
the strength of spruce.”
Used
in Sea and Air
Balsa,
while considered the softest and lightest of commercial timbers, is
classified as a hardwood. Its uses include insulation and sound-absorbtion
material, packing material, life-belts, water sports equipment, theater
props and stage furniture.
“Balsa”
is the Spanish name for raft. Constantine writes that balsa logs were used
by natives of Central and South America for making rafts, boats and
canoes. Today the buoyant wood is still used to make boats, life rafts and
bouys.
The
wood ranks as the most popular wood used in making model airplanes
designed to fly because the wood is light and strong but also easy to
work.
Adhesive
Development Catalyst
In
the book, World Timbers of North and South America, the editors write that
balsa became famous during World War II for its use as a core material
“in sandwich construction, particularly for aircraft.” The book
Encyclopedia of Wood lists balsa as one of the woods used to build the de
Havilland Mosquito aircraft. Other woods used to make the planes included
ash, spruce and birch. According to the editors, the Mosquito’s design
“forced the development of resin glues for product manufacture in
plywood; synthetic formaldhyde cement, introduced during the machine’s
production run, was found to be an improvement over casein glues for
surface jointing.” Balsa continues to be used for corestock in sandwich
construction sheets for aircraft today.
A
Challenge to Dry
Balsa’s
average weight ranges from six to 11 pounds per cubic foot. The lightest
material weighs 3 pounds per cubic foot while some balsa weighs as much as
20 pounds per cubic foot. (For comparison, white oak weighs an average of
47 pounds per cubic foot) Lighter supplies weigh roughly one-third as much
as cork. In the West Indies, balsa is known as West Indian corkwood.
Seasoning
is tricky with balsa. When the wood is green, its moisture content
typically ranges from 200 to 400 percent, with figures as high as 792
percent reported. After cutting the wood has to be converted and dried
quickly. William Lincoln, in the book World Woods In Color, writes,
“Kilning requires skilled care to avoid case hardening or toasting. It
is usually treated with water repellant to prevent absorption. Once dry,
it is stable in use with little movement.”
Balsa
can be successfully finished by staining or painting. It is known for its
natural velvet-like finish, which can be achieved by using sharp tools.
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