Chapter 3 Wood
Terms
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- bark
- A protective layer of dead material that covers a tree trunk.
- cambium
- The thin layer beneath the bark of a tree that manufactures cells of wood and bark.
- sapwood
- The living wood in the outer region of a tree trunk or branch.
- heartwood
- The dead wood cells in the center region of a tree trunk.
- pith
- A small zone of weak wood cells, located in the very center of a tree trunk surrounded by heartwood, that represents the tree's first year's growth.
- cellulose
- A complex polymeric carbohydrate of which the structural fibers in wood are composed.
- lignin
- A soft cementing substance that holds together the cells of a tree.
- grain
- In wood, the direction the of longitudinal axes of the wood fibers, or the figure formed by the fibers.
- springwood (earlywood)
- Tree growth that occurs in the spring when the weather is cool and groundwater is plentiful, conditions that favor rapid growth. Springwood cells are larger and less dense than summerwood cells, and therefore are not as strong.
- summerwood (latewood)
- Tree growth that occurs in the heat of the summer when water is scarce, which causes slower growth.
- softwood
- Wood from coniferous trees with a relatively simple microstructure compared to hardwoods. When cut into lumber, they usually have coarse and uninteresting grain patterns.
- hardwood
- Trees that are much more complex in structure than softwoods. Produce wood with much more interesting grain patterns than softwoods. More expensive.
- tracheids
- The longitudinal cells in a softwood.
- rays
- A tubular cells that runs radially in a tree trunk.
- fibers
- Small diameter cells present only in hardwoods that give the tree structural strength.
- vessels or pores
- A large diameter cell present only in hardwoods that transport sap and smaller wood fibers.
- lumber
- Lengths of squared lumber for use in construction.
- headsaw
- A large saw used to reduce a log to untrimmed slabs of lumber.
- sawyer
- The person who cuts the wood into lumber and determines how to the obtain the maximum amount of marketable wood from each log.
- plainsawing
- Sawing a log into dimension lumber without regard to the direction of the annual rings. Results in the maximum yield and therefore the greatest economy.
- quartersawn
- Lumber sawn in such a way that the annual rings run roughly perpendicular to the face of each piece.
- vertical grain
- Dimension lumber sawed in such a way that the annual rings run more or less perpendicular to the faces of each piece.
- figure
- The surface pattern of the grain of a piece of smoothly finished wood or stone.
- free water
- Water held in the cavities of a tree's cells that is first to evaporate after a tree is cut.
- bound water
- Water held within the cellulose of the cells walls which begins to evaporate after all the free water has evaporated.
- seasoning
- The process of removing water from lumber. Framing lumber is considered seasoned when is moisture content is 19% or less.
- kiln drying
- The process of drying wood in a kiln, which is faster and produces lumber with fewer distortions and more uniform quality than air drying.
- air drying
- The slow process of drying wood by stacking lumber outside.
- green lumber
- Unseasoned lumber.
- longitudinal shrinkage
- Moisture shrinkage along the length of a log.
- radial shrinkage
- Shrinkage in the radial direction. Very large compared to longitudinal shrinkage.
- tangential shrinkage
- Shrinkage around the circumference of the log. Is about half again greater than radial shrinkage.
- check
- A split along the length of a log caused by the difference between the tangential and radial shrinkage.
- parallel to grain
- In constructing building frame of plainsawed lumber, a simple distinction is made between parallel to grain shrinkage, which is negligible, and perpendicular to grain shrinkage, which is considerable.
- perpendicular to grain
- In constructing building frame of plainsawed lumber, a simple distinction is made between parallel to grain shrinkage, which is negligible, and perpendicular to grain shrinkage, which is considerable.
- surfacing
- The process of making lumber more smooth and dimensionally precise. It's run through an automatic machine that planes the surfaces and slightly rounds the edges.
- S4S
- Means that the lumber has been surfaced on all 4 sides. Most lumber is seasoned this way
- S-DRY
- A designation in a lumber gradestamp that indicates that the piece was surfaced (planed) when in a seasoned (dry) condition.
- S-GRN
- A designation in a lumber gradestamp that indicates that the piece was surfaced (planed) when green.
- growth characteristics
- Characteristics of lumber caused by the characteristics of the tree from which it came. Almost every piece of lumber contains one or more such discontinuities in its structure.
- manufacturing characteristics
- Characteristics of lumber created at the mill. Are caused mostly by changes that occur during the seasoning process because of the differences in rates of shrinkage with varying orientations to the grain.
- knot
- A common growth characteristic. Placed where branches joined the trunk of the tree. Reduces the structural strength of the piece of lumber, makes it more difficult to cut and shape, and is usually considered detrimental to its appearance.
- decay
- A common growth characteristic. May or may not affect the useful properties of the lumber depending on whether the organisms are still alive in the wood and how much damage they have done.
- knothole
- A common growth characteristic. Holes left by loose knots that fall out of the tree. Reduces the structural strength of the piece of lumber, makes it more difficult to cut and shape, and is usually considered detrimental to its appearance.
- S2S
- Many hardwoods are often surfaced on only 2 sides, leaving the 2 edges to be finished by the craftsman.
- insect damage
- A common growth characteristic. May or may not affect the useful properties of the lumber depending on whether the organisms are still alive in the wood and how much damage they have done.
- split
- A type of seasoning distortion due to shrinkage stresses.
- crook
- A type of seasoning distortion due to nonuniform shrinkage.
- bow
- A type of seasoning distortion due to nonuniform shrinkage.
- twist
- A type of seasoning distortion due to nonuniform shrinkage.
- cup
- A type of seasoning distortion due to nonuniform shrinkage.
- wane
- An irregular rounding of edges or faces that is caused by sawing pieces too close to the perimeter of the log.
- visual grading
- A way of grading structural wood where trained inspectors examine each piece for ring density and for growth and manufacturing characteristics, then judge it and stamp it with a grade in accordance with industry-wide grading rules.
- machine grading
- A way of grading structural wood where an automatic device assesses the structural properties of the wood and stamps a grade automatically on the piece. This assessment is made either by flexing each piece between rollers and measuring its resistance to bending or by scanning the wood electronically to determine its density.
- nominal dimension
- An approximate dimension assigned to a piece of material as a convenience in referring to the piece.
- actual dimension
- The actual dimensions of a piece of lumber after it has been kiln-dried.
- board
- Pieces of lumber less than 2 inches in nominal thickness.
- dimension lumber
- Lengths of wood, rectangular in cross section, sawed directly from a log that are 2-4 inches in nominal thickenss
- timber
- A piece of lumber 5 inches or more in thickness.
- board foot
- A unit of lumber volume, a rectangular solid nominally 12 square inches in cross-sectional area and 1 foot long.
- glue laminated wood (glulam)
- A piece of wood made up of a larger number of small strips of wood glued together.
- finger joint
- A glued end connection between two pieces of wood, using an interlocking pattern of deeply cut "fingers." A finger joints creates a large surface area for the glue bond, to allow it to develop the full tensile strength of the wood it connects.
- scarf joint
- A glued end connection between two pieces of wood, using a sloping cut to create a large surface for the glue bond, to allow it to develop the full tensile strength of the wood that it connects.
- structural composite lumber
- Manufactured wood product made up of either ordinary plywood veneers or of long strands of wood fiber. The grains of all the veneers of strands are oriented in the longitudinal direction of the piece of lumber to achieve maximum bending strength.
- laminated veneer lumber (LVL)
- Wood members that are made up of thin wood veneers joined with glue.
- parallel strand lumber (PSL)
- Manufactured wood components that are made of wood shreds oriented parallel to the long axis of each piece and bonded together with adhesive.
- laminated strand lumber (LSL)
- Wood members that are made up of long shreds of wood fiber joined with a binder.
- structural wood product
- A category of manufactured wood panel products.
- plywood
- A wood panel composed of an odd number of layers of wood veneer bonded together under pressure.
- veneer
- A thin layer, sheet, or facing.
- composite panel
- A wood panel composed of 2 parallel face veneers bonded to a core of reconstituted wood fibers.
- nonveneered panel
- A type of structural wood panel products that has 4 subproducts: oriented strand board, waferboard, particleboard, and fiberboard.
- oriented strand board (OSB)
- A building panel composed of long shreds of wood fiber oriented in specific directions and bonded together under pressure.
- waferboard
- A building panel made by bonding together large, flat flakes of wood.
- particleboard
- A building panel composed of small particles of wood bonded together under pressure.
- fiberboard
- A very fine grained building panel made of wood fibers and synthetic resin binders.
- medium-density fiberboard (MDF)
- The most common type of fiberboard.
- rotary sliced
- A thin sheet of wood produced by rotating a log against a long, sharp knife blade in a lathe.
- flitch
- Square blocks of wood from which veneers for hardwood plywoods are usually sliced.
- flitch sliced
- A thin sheet of wood cut by passing a block of wood vertically against a long, sharp knife.
- touch sanded
- This is done to panels intended for subfloors and floor underlayment to produce a more flat and uniform surface without seriously affecting their structural performance.
- span rating
- A way of specifying wood panels for structural uses such as subflooring and sheathing. Its purpose is to the permit the use of many different species of wood and types of panels to achieve the same structural objectives.
- exposure durability classification
- A system for rating the expected resistance of a wood panel product to weathering.
- hardboard
- A very dense panel product, usually with at least one smooth face, made of highly compressed wood fibers.
- cane fiber board
- A thick, low-density panel with some thermal insulating value; used chiefly as nonstructural wall sheathing.
- pressure impregnation
- The process of applying decay-resistant treatment to wood products.
- creosote
- A preservative applied to wood products as a decay-resistant treatment. An oily derivative of coal that is widely used in engineering structures, but because of its odor, toxicity, and unpaintability, is unsuitable for most purposes in building construction.
- pentachlorophenol
- A preservative applied to wood products as a decay-resistant treatment. Wood treated with it cannot be painted.
- waterborne salts
- The most widely used preservative in building construction.
- chromated copper arsenate (CCA)
- A chemical used to protect wood against attack by decay and insects.
- alkaline copper quat (ACQ)
- A chemical used to preserve wood against attack by decay and insects.