Physical Properties

The physical properties of a wood species are those that affect its appearance, weight, feel, and smell. Most craftsmen aren’t especially concerned about feel and smell, since these change considerably when you apply a finish. But appearance is paramount. Weight can also be important if the project is meant to be moved or carried. The chart of “Physical Properties of Wood” describes the appearance and weight of common species.

WOOD COLOR

The unique color of a wood species is determined by the chemical extractives embedded in the cell walls. But the initial color of the raw, freshly cut wood doesn’t remain unchanged. This color darkens somewhat when you apply a finish, even if that finish appears clear and colorless. Most finishes also change the hue, making it more amber. Craftsmen describe this as “warming up” the wood color. In the chart of “Physical Properties of Wood,” you can see how common finishes affect color.

Unfortunately, what you can’t see is that the wood also changes color with age. As the surface of the wood is exposed to air, it slowly oxidizes. Some woods are photosensitive — exposure to ultraviolet light alters the extractives. Both reactions change the wood color at the surface. This thin layer of color-changed wood, sometimes only a few thousandths of an inch thick, is the patina.

Cherry is a photosensitive wood. The escutcheon that once adorned this cherry drawer front blocked the light. Consequently, the patina where the escutcheon once was is much lighter than the surrounding wood. The patina of most woods grows darker with age. However, in two species — walnut and mahogany — it grows lighter. As they age, their patina becomes a soft gray color.*

Scrapwood

When restoring or refinishing antiques, be careful not to sand through the patina. If you do, the wood may appear blotchy – darker in some areas than in others.

WOOD TEXTURE

Texture depends on the size of the longitudinal cells. In hardwoods, this refers to the size of the fibers and the vessel elements; in softwoods, it’s the tracheids. Fine-textured woods have small cells, while coarse woods have larger ones.

WOOD GRAIN

When the vessel elements in hardwoods are sliced open, they create depressions called pores. Woods with large pores that are easily visible to the naked eye are said to have an open grain. Those with smaller pores, to small to see clearly, have a closed grain. Note: Because softwoods do not have vessel elements, these terms don't apply. For practical purposes – such as preparing and finishing the surface – softwood grain is closed.

red oak, cherry, and southern yellow pine at 25x maginification

Red oak (top) has extremely large vessel elements which form visible pores when sliced open. The long grain surfaces are said to have open grain. The vessel elements of Cherry (middle) are much smaller, they do not form visible pores, and the surfaces have closed grain. Southern Yellow Pine (bottom) has no vessel elements, just an occasional resin canal. The grain is neither open or closed.*

GRAIN PATTERN

The normal orientation of the longitudinal cells determines a species’ characteristic grain pattern. There are four categories.

In straight grain, the longitudinal cells grow fairly straight and parallel to the axis of the trunk.
In wavy grain, the cells undulate in short, even waves. This sometimes produces curly figure.
In irregular grain, the cells undulate around knots or in no discernible pattern.
In interlocked grain, the cells spiral around the trunk, reversing direction every few growth rings. This produces ribbon figure.

close up of straight, wavy, irregular, and interlocked grain

The long grain surfaces of sawn lumber may display four types of grain patterns.*

WOOD WEIGHT

The weight of a species can be gauged from its specific gravity. The higher the specific gravity, the heavier the wood. To figure the precise weight of a board foot (1 ✕ 12 ✕ 12 inches) of a wood, multiply its specific gravity by the weight of a cubic foot of water, 62.5 pounds, then divide by 12. The weight of cherry, for example, is 2.6 pounds per board foot:

0.50 ✕ 62.5 ÷ 12 = 2.6

Outside of North America, wood is sold by the cubic meter and weight is calculated in kilograms. To figure the weight of a species, simply multiply the specific gravity by 1000. Cherry weighs 500 kilograms per cubic meter.

0.50 X 1000 = 500

USING THE CHART

The chart of “Mechanical Properties of Wood” is divided into three parts -- North American Hardwoods, North American Softwoods, and World Woods, or woods from other places than North America. To access any part, click on the title below. To see the properties for any wood species, click on its name.

North American Hardwoods

North American Softwoods

World Woods (Other Than North America)

Tree Trivia:

The fattest tree in the world is the "Great Banyan" in the India Botanical Gardens near Kolkata. The circumference of the main trunk is 52 feet and the crown shades 4 acres.

You can tap birch trees for their sap and make syrup much the same as maple trees. Birch syrup is easier to digest, has a lower glycemic index, and is higher in nutrients than maple syrup.

The average 2000-square-foot house requires 16,000 board feet of lumber and 11,000 square feet of sheet materials.