California black oak

Date: 2007-11-21

by Gene Wengert

Tight grain, high-density is weaker than most red oaks, but machines better. It is not as red, has a tighter grain and drying is difficult.

California black oak (Quercus Kelloggii) is in the red oak group of species. It grows primarily in northern California and southwest Oregon, and is weaker than most red oaks, but machines better. It is not as red, has a tighter grain and drying is difficult.

This species of red oak, also called western red oak, and in its growth area black oak, is tremendously underused. Too many people may have tried to use softwood drying equipment and techniques to dry this very refractory (prone to surface checking and cracking) wood. The drying results were disastrous. However, with proper "Southern oak" drying procedures and conditions, this oak can be dried without much defect development.

Another reason for underuse is the sparsity of NHLA graders in the area; the grading scheme is one of the marketing keys for any hardwood. Finally, the typical mill supply of logs produces 38 percent No. 1 Common and Better lumber, which is marginally low and will require good markets for the lower grades in order to be profitable. Some mills have developed proprietary grades for so-called "low grade" material; in reality, low grade is a valuable raw material for many manufacturers.

Processing suggestions and characteristics

Weight measurement. This is a fairly heavy wood, but is slightly lighter than eastern red oak. 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 40 pounds per cubic foot or 3.3 pounds per board foot.

Strength. Due to its moderately high density, California black oak's strength and stiffness is high, although slightly weaker than eastern red oaks. For dry wood, the ultimate strength (MOR) is 13,000 psi and hardness is 1,100 pounds. Comparative red oak values are 14,300 psi and 1,290 pounds.

Drying and stability. The wood dries slowly, with a high risk of checking and honeycomb. Slow shed-air drying with plastic mesh curtains to avoid excessively rapid drying conditions is essential. Kiln drying green-from-the-saw is also acceptable quality-wise, but is expensive time-wise. End coating is required to prevent end cracking. Other proper drying practices are essential. Most suppliers will sell only KD stock, rather than green. It is critical to check incoming stock for checking and honeycomb before accepting a load.

Shrinkage in drying of 9.7 percent is lower than for eastern red oaks. 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, unless used in a humid location. It takes a 4 percent MC change to result in 1 percent size change tangentially and 7 percent MC change radially.

Machining and gluing. This wood machines well, better than eastern red oaks. Being higher in density, it does require sharp tools and proper machine setup to avoid chip-out. Avoid drying the lumber under 5 percent MC.

This wood glues with considerable difficulty. Surfaces must be freshly prepared and flat to achieve satisfactory joints with conventional adhesives.

Grain and color. The heartwood is light tan with a reddish hue, but is not as red as many other red oaks. The grain is finer, and not as porous as most southern and many eastern red oaks. The grain pattern in lumber from open grown trees can be erratic (full of character).

California black oak

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