Wood Definitions

Is it Timber or Wood?

Dictionary definition:

Timber:- 1 Wood prepared for building, carpentry, etc,. 2 Piece of wood.
Wood:- 1 Growing trees. 2 Fibrous substance between pith & bark of tree.

The word "wood" is commonly used in many different situations i.e. woodcut, wood pulp, wood wasp, whereas "timber" is not. An old UK technical book on timber has a heading "The seasoning of wood" with a line "piece of timber". An American book "Successful Wood Book" uses the word "Lumber" instead of "Timber". Paint cans and packets of filler always use the word "Wood".
To be consistent the word "Wood" will be used.

Air-dried See Seasoning.
Annual growth ring. Layer of wood growth put on a tree in a single growing season. May be in two visible bands, the spring and summer growth.
Bark. This is the tree's outer protective layer that protects it from heat, weather, insects and animals. The bark also prevents the tree from loosing moisture. Bark is made from the outer layers of the bast as they die.
Bast. (or phloem) Thin green layer of tube-like cells that supply Elaborated Sap to the sapwood.
Beam. Load carrying member, supported at both ends.
Cambium. Thin layer of tissue surrounding the sapwood that repeatedly subdivides to form new sapwood and bast cells.
Cell. A general term for the structural units of the tree tissue, which include wood fibres, vessel members and other elements of diverse structure and function. Difference in cell characteristics account for different properties and performance and appearance of the various woods.
Cellulose. Carbohydrate that is the principal constituent of wood and forms the framework of the wood cells.
Check. A lengthways separation of the wood that usually extends across the rings of annual growth and commonly results from stress set up in the wood during seasoning.
Chipboard. Chips of different woods combined with a resin to form a sheet material.
Coniferous. Trees that keep their needle-like leaves throughout the year and grow tall and slender. (=softwoods)
Deciduous. Trees that loose their broad leaves each year. (=hardwoods)
Density. The mass of wood substance enclosed within boundaries of a given unit of volume. Kilograms per cubic meter. Used for costing and comparison of woods.
Dowel. A round wooden pin often inserted into matching holes of two pieces of wood to strengthen the joint.
End Grain. Refers to the grain as seen on a cut made at a right angle to the direction of the fibres, as on the cross section of a tree.
Fibreboard. Man made sheet material made from pulped wood bonded with resins. Insulation boards, Hardboard and M.D.F.
Figure. The pattern produced on the surface of wood by the annual growth rings, rays knots, interlocking and wavy grain etc..
Filler. Any substance used to fill holes and irregular surfaces to decrease the porosity of the surface before applying the finishing coats.
Finish. Coatings of paint, varnish, lacquer, wax, etc., applied to the wood surface to protect, waterproof and enhance their durability and appearance.
Grain. The direction, size, arrangement, appearance, or quality of the fibres in wood.
Close-grained wood has narrow, inconspicuous annual rings giving a fine texture. Small closely spaced pores in hardwoods.
Open-grained wood has a visible grain pattern (figure) and a course texture. Large pores in hardwoods.
Interlocking-grained wood has the grain running in different directions and this makes it very difficult to cut and finish.
Straight-grained wood has all the fibres running parallel to the centre of the tree and this makes it the easiest wood to cut and finish.
Green. Freshly sawn or undried wood. Not normally used in woodwork.
Hardboard. Thin fibreboard material made by compressing wood pulp fibres mixed with resin into hot metal moulds. Theses moulds can be flat, patterned or shaped like doors.
Hardness. A property of wood that enables it to resist indentation.
Hardwood. The fibres in Hardwoods are small and are not used to transport the crude sap from the roots to the leaves. This is carried out by Pores. Hardwood trees can be soft or hard. They are usually Deciduous.
Heartwood. Wood extending from the pith to the sapwood, the cells of which no longer take part the life process of the tree. Heartwood may contain phenolic compounds, gums, resins, and other materials that usually make it darker and more decay resistant than sapwood. This is the part of the tree that is used.
Joint. Junction of two pieces of wood.
Kiln-dried. See seasoning.
Knot. The portion of a branch which has been surrounded by subsequent growth of the stem. The shape of the knot as it appears on the cut surface depends on the angle of cut of the wood.
Loose Knot is one that is not held firmly in place by growth or position and cannot be relied on to remain in place. It adds no strength to the wood and must be avoided if possible.
Sound knot is one that is solid across its face, at least as hard as the surrounding wood, and shows no indication of decay.
Laminated wood. Strips of wood are glued together with all their grain directions parallel. The wood can be straight or bent around a former. Very long roof beams can be made with a varying thickness. Tabletops can be made by gluing strips of wood side by side with the end grain being alternated to avoid warping. End joints of the strips must not be adjacent.
Lignin. The second most abundant constituent of wood, located principally in the secondary wall and the middle lamella, which is the thin cementing layer between wood cells.
Manufactured Boards. Sheet material made from wood pulp (fibreboard), chips (chipboard), strips (blockboards) and veneers (plywood).
M.D.F. Medium Density Fibreboard
Mitre. Wood cut at an angle usually to form a right angle joint.
Moisture Content. The amount of water in the wood. Wood is dried in a kiln until its moisture content is about 14% (=seasoning)
Mortise. A slot cut into wood to receive another piece of timber.
PAR. Planed on All Sides. Wood is cut into various sizes and then planed to give a smooth surface.
Parquetry. Hardwood flooring made from small blocks rather than strips.
Particleboard. A sheet material made from wood particles (not fibre pulp) bonded together with a resin under heat and pressure. Example - Chipboard.
Patina. The mellow, soft appearance of wood which has had years of use and has been affected by light, air and tiny dents and scratches.
Phloem. See Bast.
Pith. The small soft core occurring near the centre of a tree trunk, branch or twig. Often the remains of the sapling. Avoid using wood with pith.
Plumb. Another term for vertical. Use a plumb line to draw vertical lines on a wall.
Plywood. A sheet material made by gluing thin sheets of wood together with the grain directions alternated at right angles to each other.
Each sheet of wood is about 1mm thick and is called a ply. Plywood is made up of an odd number of plies and is strong in all directions. Exterior plywood is made using waterproof glues.
Preservatives. Any substance that stops wood from decaying.
Quarter Sawn. (Radial Sawn) Tree logs are first cut into quarters and then cut at an angle. This expensive but it produces the best wood. (=Hardwoods)
Raised grain. This is a condition where the fibres of the wood stand out at right angles to the wood surface giving a rough finish. The first coat of paint, varnish or stain always raises the grain and must be sanded off.
Rays. Strips of cells extending radially within the tree and varying in height from a few cells to over 100mm in oak. Rays serve primarily to store food and transport it horizontally in the tree. Rays can produce a distinct figuring in some woods.
Resin. This is hardened Elaborated Sap that remains in the Heartwood.
Rip. To cut lengthways, parallel to the grain.
Rough Sawn. Wood is cut into various sizes and left in the rough surface finish.
Sap. Crude Sap is the liquid made up of water and minerals that is sucked up the tree from the roots to the leaves.
Elaborated Sap is the tree's liquid sugar food coming down from the leaves to the sapwood. It is made from Crude Sap by the action of sunlight.
Sapling. Young tree.
Sapwood. The pale coloured wood near the outside of the tree. Under most conditions, sapwood is more likely to decay than heartwood.
Seasoning. Removing moisture from green wood to make it usable.
Air-dried: wood is left out in the open air under cover from the rain. This is the best method of seasoning as the moisture in the wood slowly dries out. Used for expensive hardwoods.
Kiln-dried: Moisture is removed rapidly in an oven. It is a cheap method but can cause warping.
Shake. These are splits along the grain inside the tree along the annual growth rings.
Shrinkage. Wood contracts as it dries out. Correctly dried wood expands and contracts during the year as its moisture content changes. Paints etc. do not always completely seal the wood so let moisture pass both ways. Care must be taken when using wood as its expands more across than along the grain.
Slab Sawn. The tree logs are cut into parallel slices or slabs of wood which are then dried. This is the cheapest and quickest method of producing wood. (=softwoods).
Softwood. Fibres in Softwoods are long (6mm) and thin. Crude sap is transported from the roots to the leaves through apertures in the fibres called pits. These fibres support the tree. Softwoods can be hard or soft. They are usually coniferous.
Springwood. The portion of the annual growth ring that is formed during the early part of the growing season. Usually less dense and weaker mechanically than summerwood.
Summerwood. The portion of the annual growth ring that is formed during the later part of the growing season. Usually denser and stronger than springwood.
Tenon. This is the end of a piece of wood cut to fit into a mortice to form a strong joint.
Veneer. A thin sheet of decorative wood glued onto a thick piece of wood, chipboard or MDF.
Warping. When trees are first cut into lengths and sizes, the natural forces (stresses) locked up inside the tree are released. This can cause the wood to deform in different directions such as twisting, cupping, bowing or bending.
Weathering. Mechanical or chemical disintegration and discolouring of the surface of the wood caused by exposure to light, the action of sand and dust carried by the wind, and the alternate shrinking and swelling of surface fibres with the continual variation in moisture content brought by changes in the weather. Weathering does not include decay.
Workability. The degree of ease and smoothness of cut obtained with hand or machine tools.
Xylem. See Sapwood.


Issue 33 - 23/05/03