California black oak: An oak with several differences
California Black Oak grain

California black oak is in the red oak group of species, but its source of supply (it grows primarily in northern California and southwest Oregon), physical properties (it is weaker than most red oaks, but machines better), appearance (it is not as red, but has tighter grain), and processing differences (drying is difficult) merit a special discussion of this species.

The tree reaches maturity in 90 years or longer. At that age it is 50 to 100 feet high and 14 to 40 inches in diameter; the larger sizes are when the tree is growing on good sites. On poor sites, the tree is quite scrubby in appearance. The acorns were widely used as a food by Native Americans, often being dried and ground into flour. Unfortunately, many of the California black oak trees have died in recent years due to a fungal disease, commonly called “Sudden Oak Death.”

This species of red oak, also called Kellogg oak and western red oak, and in its growth area, black oak, is tremendously underutilized. The wood makes excellent lumber that is well suited for furniture, cabinets, and flooring. Developing special grading rules or adjusting the standard rules may prove to be rewarding.

Because there is not a well-developed market, buyers must contact potential sawmills personally. Then try a few sample pieces of lumber that can be tested. 

Appreciate that most sawmills do not carry an inventory of this species, so may not be able to provide needed quantities year round. You might have to use lower grades than you are used to, or assist in locating users of lower grades if you only take the higher grade. 

Processing suggestions and characteristics
Density. The green specific gravity (SG) is 0.61; at 6 percent MC, the SG is 0.67. The weight, when dried to 6 percent MC, is 39 pounds per cubic foot or 3.3 pounds per board foot.

Drying. The wood dries slowly and with a high risk of checking and honeycomb. End coating is also required to prevent end cracking. Shrinkage in drying of 9.7 percent is lower than for eastern red oaks.

Gluing and machining. This wood machines well, although being higher in density, it does require sharp tools and proper machine set-up to avoid chip-out. Avoid drying the lumber under 5.5 percent MC. This wood, as with all higher density species, glues with considerable difficulty. Surfaces must be freshly prepared and flat to achieve satisfactory joints with conventional adhesives.

Stability. Once dried, the wood will move substantially, although less than eastern red oaks, if there are large RH changes or if the MC is not matched to the environment’s EMC conditions. A typical final MC range is 6.0 to 7.5 percent.

Strength. For dry wood, the ultimate strength (MOR) is 13,000 psi and hardness is 1100 pounds. 

Color and grain. The heartwood is tan with a reddish hue, but it is not as red as many other red oaks. Because of California black oak’s slow growth, the grain is finer than most southern and many eastern red oaks. The grain is coarse. Stain penetration is variable at times, due to tension wood, which is common in open-grown trees especially.


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About the author
Gene Wengert

Gene Wengert, “The Wood Doctor” has been training people in efficient use of wood for 45 years. He is extension specialist emeritus at the University of Wisconsin-Madison.