Two major spruces are found in the western forests of the United States. Engelmann spruce (Picea engelmannii) is found throughout the Rocky Mountains, from Alberta to Arizona. It’s named after George Englemann, who discovered this species in the mid-1800s.
Sitka spruce (Picea sitchensis) 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 Alaska’s state tree.
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 more than 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 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, and sailing ship masts.
Processing suggestions and characteristics
(Wood from these two trees is nearly identical in processing and properties; Englemann is slightly lighter and weaker. Data is for Sitka.)
Density: Sitka spruce weighs about 27 pounds per cubic foot. A piece of 1 inch x 6 inch x 12-foot lumber (actual size 3/4 inch x 5-1/2 inch x 12 feet) will weigh about 9 pounds at 9 percent MC.
Drying: It’s important that lumber for remanufacturing not be over-dried (dried under 9% MC) or the wood can become brittle when machining. Shrinkage in drying is 3% (quartersawn) to 6% (flatsawn).
Gluing and machining: Gluing is excellent. Dry wood absorbs glue, so use adequate spread rates to prevent starved joints. Machining is excellent if tools are sharp and machine pressures not high. Chipped grain is common when machining close to a knot.
Stability: Spruce is fairly stable, requiring about 4% MC change to have a size change of 1% (tangential direction). For quartersawn lumber, a 7% MC change causes a 1% width change (radial direction).
Strength: Spruce is a 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. Spruce is only 14 percent heavier than Eastern White Pine, yet is 20% stronger, 25% stiffer and 34% harder. Compared to hardwoods, spruce needs slightly larger fasteners to obtain higher fastening power.
Color and grain: Sapwood is creamy white, but the heartwood is pinkish yellow, becoming somewhat darker with exposure to light. The grain is very fine and straight. Some people report skin allergies from contact with the wood, especially the fine dust.
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