Q. We are making hickory dowels and have two questions: Why are some dowels more pink in color and why are some apparently weaker than others. The last thing we need is a broken chair rung or even a leg.

A. Although you are asking about dowels, the answer applies to all wood.

Color
Most of the white, light-colored wood, almost always sapwood, has sugars and starches. These chemicals can oxidize slowly and the result is pink, grey, brown and other colors within the wood. The warmer the wood, the faster discoloration occurs. High humidity and resultant slow drying also encourage oxidation. 

To achieve the whitest, brighter color in wood, we need to move quickly after harvesting the tree. In warm weather, we should try to saw the log into lumber within a few days after harvesting. Then, after sawing, the lumber should be stacked and moved into the dry kiln within 24 hours in warm weather. In the kiln, cool temperatures and drying with appropriate humidity and air flow will assure fast drying, which limits oxidation reactions. This is essentially 100% perfect control of the color. 

Strength
Clear wood has a certain strength inherent for the species. Strength is affected by density, so avoid any wood that is lighter weight than is normal for the species. Strength is also affected by moisture content, so make sure the wood is under 8.0% MC.

The most overlooked factor in strength is the grain angle, especially in a small diameter item like a dowel. If we assume that hickory at 8% MC is 100%, then the strength related to angle is: 

Angle    Strength
0 degree    100%
5                  92
8                  83
12                58
15               44

Appreciate that 12 degrees is a very small angle. This grain angle in a few species, mainly softwoods, is determined by the tree’s growth. A crooked tree also has steep growth angles. Likewise, the wood near a knot also can have steep grain angles. But, in most hardwoods, it is the sawyer’s positioning of the log on the carriage that determines grain angle. The rule is that the best grain angle is when we saw parallel to the bark, and not parallel to the center of the log.

Q. We have a client that purchased our cabinets and now has an issue with the wood floor. The new oak floor has developed cupping, so that the edges of the individual strips are raised. You can feel every bump and see this pattern as well. What has happened?

A. Unfortunately, this is a frequent issue when wood floors are exposed to a sudden high humidity on the top surface. Consider that this floor has maybe 100 strips of oak adjacent one to the other. All of sudden, moisture hits the top surface, penetrates the finish and gets into the top wood fibers. 

Increasing the moisture of wood fibers causes them to swell. In the case of water, the wood surface can be trying to swell as much as 7%. But the wood underneath the surface is not swelling, and the adjacent flooring pieces also allow no room for swelling. So, what happens in order to relieve the surface swell stress, the wood near the edges is pushed upward. This creates a little bump. 
Because this happened quickly, this deformation of the wood is not recovered when the water evaporates —  the bump is more or less permanent. (Note: when wood changes MC slowly, often the stress is relieved over time because the wood is plastic; that is, the wood flows. Therefore, slow changes of moisture are not near as important as fast.)

So, the bottom line is that the customer is stuck with these bumps unless they want to sand them smooth. Repeated use of water on the surface, especially if the water does not evaporate quickly before it penetrates the finish, will make things worse. You can purchase wood floor cleaners that contain water, but they also will evaporate quickly if properly applied.

A wood floor installed over a damp crawl space can also result in similar problems.

Q. We make wood cutting boards. We notice that sometimes, usually after the surface gets wet and is not dried quickly, that the joints of the individual pieces are raised, so that the surface is no longer smooth to the touch. Can you tell me what is happening?

A. Let’s consider two pieces or staves glued, edge to edge. Their overall moisture, after the glue dries in a few days, is a uniform 7.0% MC. They are then assembled, sanded, and finished into a final product.  Consider that the surface coating, which is likely somewhat waterproof, wears away, so now water on the surface causes an immediate increase in the wood’s surface MC. A rapid increase in moisture causes swelling of the surface, while the rest of the two pieces has no size change. So, the surface tries to expand, but is restrained from moving by the core. The large, solid core stops the individual pieces from cupping, at least initially. So, the surface’s only choice is to move upward at the joints, creating a ridge. 

If the moisture evaporates slowly, will the surface return to being flat? No. Because this swelling movement was really fast, the wood took on a permanent shape change. Subsequent slow drying will not return the wood surfaces to “normal,” and the ridge remains.

Also, if the glue joint is not “up to snuff” which means that the joint is not 1.5 times stronger than wood, there may be a small crack in the joint that opens wider in the drier, winter weather.

The ultimate cure is to avoid wetting of the surface by using and maintaining a waterproof coating.