WOOD EXPLORER
by Gene Wengert
ewengert@wisc.edu
Redwood
Lightweight, even
grained and red
in appearance.
Redwood (Sequoia sempervirens) is
a wonderful evergreen species, with
mature trees commonly reaching 300 feet
high and 12 feet in diameter. (Giant sequoia is even larger and is a different species.) In North America, redwood grows
primarily in California. Although much of
the California redwood forests have been
harvested or are now reserved, there are
still good supplies, albeit expensive, of
redwood logs available from replanted
forests, sometimes called second growth,
both in California and in New Zealand. In
fact, in New Zealand redwood trees grow
so rapidly that within 50 years they are
gigantic and ready for harvest.
The wood itself is lightweight and even
grained. It is very red appearing, although
second growth may be somewhat lighter
in color and in weight. Redwood is known
for its low shrinkage and its natural decay
and insect resistance. For many years,
redwood was the preferred species for
house siding and decks.
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There are more than 30 lumber
grades for redwood. As a rule of thumb,
when the lumber is all heartwood, which
will give the maximum protection against
decay and insects, the grade name will
contain the wood “heart.” Major grade
divisions include architectural (top
clearness) and garden, and heart and
sap. The Redwood Inspection Services
( www.redwoodinspection.com/grades.
html) monitors grading for this species.
In addition to sawing logs into lumber,
there are also active manufacturing pro-
cesses using old timbers and old lumber
remanufactured into products for today.
Redwood is so valuable and durable
that recycling is socially responsible and
makes economic sense as well. Some
old-growth redwood logs are available
from forests where the trees have been
blown down and have been sitting on the
ground for 50 years or more. Redwood
veneer products are also popular. ❮
Density. Redwood weighs about 23
pounds per cubic foot. Most other softwood species are somewhat heavier. The
lumber weighs about 1-1/2 pounds per
board foot, kiln-dried and surfaced.
Gluing and Machining. Redwood
glues very easily. The open structure
requires a little more adhesive than
with heavier woods. Avoid excessive
pressure.
Machining is excellent if the tools
are sharp. Dull tools tend to push
over or mash the fibers, not cutting
them cleanly. Sharp sandpaper is also
important using light pressure.
Strength. Redwood is fairly weak,
as might be expected from its low
density. Its strength (MOR) is approximately 7900 psi, which is a little
weaker than Eastern white pine (8600
psi). Its stiffness (MOE) is 1. 1 million
psi. Hardness is 420 pounds.
Processing suggestions and characteristics (Second growth)
Drying. Drying requires care to avoid
severe end splits and collapse. Slow
careful drying is the rule, with end
coating being essential. With older
growth, water pockets and areas of
collapse are common. Steaming after
drying to recover collapse is required
when collapse occurs.
Shrinkage from green to 10 percent MC is only about 3 percent; most
other species would be over 5 percent
shrinkage.
Final moisture contents can be 10
to 12 percent MC.
Stability. The low shrinkage means
that the wood is very stable when the
MC changes in use. This property
means low warp in-use. It also means
that when painted, there will be little
stress on the paint film, so the paint
will adhere and last for years even
when there is a lot of wetting and drying of the wood.
Color and Grain. Redwood is almost
all heartwood, which is very red in
color. The outer rings of the tree are
white sapwood, but little of this is
included in lumber.
The grain of redwood varies
somewhat from tree to tree. Typically,
the wood is soft and fine grained, but
sometimes the grain is very coarse (or
open). The grain is straight and not
as distinctive as with most pines, for
example.
