Two major spruces are found in the western forests of the U.S. Engelmann spruce (Picea engelmannii) is found throughout the Rocky Mountains, from Alberta to Arizona. It is named after George Englemann who discovered this species in the mid 1800s. Sitka spruce is found primarily within 50 miles of the Pacific Coast from Alaska to northern California. The name comes from Sitka Island where the tree was discovered in 1892; Sitka spruce is also the state tree of Alaska.
Spruce trees are one of the largest trees in the western forests, often reaching 175 feet in height and 3 to 6 feet in diameter. They may live 700 years. A record sized tree in Oregon is nearly 17 feet in diameter and over 215 feet high.
For their weight, the spruces are exceptionally strong. Hence, spruce has been used for airplanes, including propellers, where high strength was required, but weight needed to be as low as possible. (Note: Howard Hughes’ “Spruce Goose” airplane was notmadeofspruce, but used primarily birch.)
Thin panels of Sitka spruce are noted for their very good sound resonance. Hence, they are preferred for quality piano sounding boards. Spruce is also used for other stringed instruments, such as guitars. Other uses for spruce include furniture, millwork, cabinets, sailing ship masts and other components,andcooperage. Often these spruces are mixed in with true firs or other softwoods species and are not sold separately.
Processing suggestions and characteristics
(The wood from these two trees is nearly identical in processing and properties; Englemann is slightly lighter weight and slightly weaker. Data below is for Sitka.)
Density.
Sitka spruce weighs about 27 pounds per cubic foot. A piece of 1 x 6 x 12′ lumber (actual size (3/4″ x 5-1/2″ x 12′) will weigh about 9 pounds at 9 percent MC.
Drying.
In general, spruce dries very easily. It is important that lumber intended for remanufacturing not be over-dried (dried under 9 percent MC) or the wood can become too brittle when machining. Shrinkage in drying is 3 percent (quartersawn) to 6 percent (flatsawn).
Gluing and Machining.
Gluing is excellent. Dry wood does absorb glue quickly, so adequate spread rates are required to prevent a starved joint.
Machining is excellent if tools are sharp and any machine pressures are not high. Chipped grain is common when machining close to a knot.
Stability.
Spruce is fairly stable, requiring about 4 percent MC change to have a size change of 1% (tangential direction or the width of flatsawn lumber). For quartersawn lumber, a 7 percent MC change will cause a 1 percent width change (radial direction).
Strength.
Spruceisan moderately strong wood for its size, but for its weight is very strong. The strength (MOR) is 10,200 psi; stiffness is 1.57 million psi; and hardness is 510 pounds. (Eastern white pine values are 8600 psi, 1.24 million psi and 380 pounds. Spruce is only 14 percent heavier than EWP, yet is 20 percent stronger, 25 percent stiffer and 34 percent harder.)
Compared to hardwoods, spruce needs slightly larger fasteners (including head size) to obtain higher fastening power.
Color and Grain.
The sapwood is creamy white, but the heartwood is pinkish yellow, becoming somewhat darker with exposure to light. Lumber can all sapwood, all heartwood or mixed.
The grain is very fine and straight.
Some people report skin allergies from contact with the wood, especially the fine dust.