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 here in the 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. Interestingly, for such a large tree, the cones are scarcely 1 inch in length!
The wood itself, which is mostly heartwood, is lightweight and even grained. It is very red appearing, although second growth may be somewhat lighter in color and in weight. I believe the key properties of redwood lumber that have made it so popular are its low shrinkage (meaning good paintability, little warp in use, and so on) and its natural decay and insect resistance. For many years, redwood was the preferred species for house siding (excellent paint holding) and decks. Another popular use was for water towers for railroad steam engines.
There are over 30 lumber grades for redwood lumber. 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 California Redwood Association is active in marketing redwood lumber. The Redwood Inspection Services (www.redwoodinspection.com/grades.html) monitors grading for this species.
In addition to sawing logs into lumber, there is also active manufacturing processes using old timers and old lumber that is remanufactured into products for today. Redwood is so valuable and durable that recycling is socially responsible and makes economic 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, although only a little redwood is used, with the core veneers being a more available for lumber production at times.
Processing suggestions and characteristics (Second growth)
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.
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.
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.
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.
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.
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.
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