Whenever we do a little reading about the way things were in our industry in the “old days,” meaning the 1920s and 1930s, we find out that one of the major species back then was sweetgum (Liquidambar styraciflua). The name liquidambar is from the common name in Mexico (indirectly from Latin, meaning liquid and amber) in reference to the fragrant resin. 

The yellowish colored sap (technically called gum in a hardwood tree) is exuded from bark wounds and can actually be boiled down and concentrated into a salve that will reportedly cure skin problems and other ailments. 

The tree is common from Missouri to Connecticut and all states south of there, but lumber production is primarily in the southern states.

Even though plentiful, sweetgum lumber is not seen in most sawmills and therefore not seen in most furniture plants. Yet, it is one of my favorite species. I think that it is overlooked as a premium, moderately strong wood.

In the marketplace sweetgum is sold as either sap gum (which is the light colored sapwood) or red gum (which is the reddish-brown heartwood).

Incidentally, the Australian nursery rhyme that begins “Kookaburra sits in the old gum tree, eating all the gumdrops he can see.” is not referring to the sweetgum tree, but to one of the Australian eucalyptus trees. However, the expression “up a gum tree” which means “in great difficulty” or “in a sticky situation” is apparently American in origin. There is also an old musical song (circa 1824) that was also danced to entitled “Possum Up a Gum Tree” which was from South Carolina and referred to the sweetgum.  

Processing suggestions and characteristics
Density. Sweetgum has a density of approximately 33 pounds per cubic foot. Sweetgum KD lumber weighs about 3 pounds per board foot at 7 percent MC.

Drying. The wood has interlocked grain and it warps. Flatsawn wood has a tendency to cup. Overall, gum shrinks 8 percent from green to 6 percent MC. Sap gum, like most sapwood, is subject to rapid discoloration by blue stain fungi and chemical gray stain in warm weather. Red gum will honeycomb if dried too quickly.

Gluing and machining. Sweetgum glues fairly easily, but because of the interlocked grain, any change in MC will likely affect surface flatness, thereby affecting glue bond strength. Sanding requires fresh (sharp) sandpaper. 

Stability. Gum shrinks and swells a more than some hardwoods (1 percent size change for a 3 percent MC change). Further, the interlocked grain can cause some unusual shrinkage problems. I suggest 6.5 percent MC to 7.0 percent MC as the target for most users. 

Strength. The strength (MOR) at 12 percent MC is 12,500 psi, Stiffness (MOE) is 1.64 million psi, and hardness is 850 pounds.
Color and grain. Red gum has its own wonderful, busy character often with long streaks of various dark colors and interlocked grain. This interlocked grain creates a long ribbon like appearance, very similar to mahogany. The concern over drying has been blown out of proportion and has led to a negative connotation when sweetgum is mentioned.