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Question 1Wood science: timber structure, growth, seasoning and moisture behaviour

In a mature softwood stem, which statement correctly describes the difference between heartwood and sapwood?

  1. Sapwood lies at the centre of the stem and is darker because extractives have accumulated there over many years
  2. Heartwood no longer conducts sap, and extractives deposited in it usually darken the wood and reduce its permeability Correct answer.
  3. Heartwood occupies the outer zone of the stem and has the highest starch content, so it stains readily
  4. Sapwood consists of dead, extractive-filled cells, whereas heartwood is the living sap-conducting zone

Explanation

Heartwood is the inner, non-conductive wood left behind as the cambium adds new sapwood; as the cells die, extractives such as tannins and resins are deposited, which darken the wood, block pit membranes and lower permeability. Sapwood remains the outer, sap-conducting zone and normally holds more moisture and starch.

Question 2Wood science: timber structure, growth, seasoning and moisture behaviour

At the fibre saturation point, which condition applies to the cell walls and the lumens?

  1. The cell walls are fully saturated with bound water while the lumens contain no free water Correct answer.
  2. The cell walls are oven-dry and the lumens contain only tightly bound water
  3. The cell walls hold about half their maximum bound water and the lumens are partly drained
  4. Both the cell walls and the lumens are completely filled with water, as in freshly felled timber

Explanation

The fibre saturation point is reached at roughly 28-30% moisture content, when every sorption site in the cell wall is occupied by bound water but the lumens are still empty of free water. It matters because nearly all shrinkage, swelling and strength change takes place only below this point.

Question 3Wood science: timber structure, growth, seasoning and moisture behaviour

Within a single growth ring of a conifer, how do earlywood and latewood tracheids compare?

  1. Earlywood is formed in summer and has thick walls with narrow lumens
  2. Earlywood has thin walls and wide lumens, while latewood has thicker walls, narrower lumens and higher density Correct answer.
  3. Both zones have the same wall thickness, but latewood contains more extractives
  4. Latewood is formed first in spring and has thin walls with wide lumens

Explanation

Earlywood is laid down at the start of the growing season, when tracheids are produced quickly with thin walls and wide lumens for conducting sap. Later in the season latewood forms with thicker walls, narrower lumens and denser material, so each ring shows a distinct density gradient.

Question 4Wood science: timber structure, growth, seasoning and moisture behaviour

Which pairing of reaction wood type, species group and position in a leaning stem is correct?

  1. Tension wood, softwoods, upper side of the lean
  2. Compression wood, hardwoods, upper side of the lean
  3. Compression wood, softwoods, upper side of the lean Correct answer.
  4. Compression wood, softwoods, lower side of the lean

Explanation

Softwoods respond to a leaning or displaced stem by producing compression wood on the lower side, where high lignin content and a large microfibril angle generate swelling stress that pushes the stem upright. Hardwoods instead form tension wood on the upper side, recognised by a gelatinous G-layer rich in cellulose.

Question 5Wood science: timber structure, growth, seasoning and moisture behaviour

Which cell wall layer governs the longitudinal stiffness and longitudinal shrinkage of a softwood tracheid?

  1. The S2 layer, the thickest wall layer, whose microfibrils lie at a shallow angle to the cell axis Correct answer.
  2. The warty layer lining the lumen, which controls the uptake of water into the cell
  3. The middle lamella, which cements adjacent tracheids together and is rich in lignin
  4. The S1 layer, the outermost secondary wall layer, whose microfibrils run almost transversely

Explanation

The S2 layer makes up most of the secondary wall volume and its cellulose microfibrils are wound at only about 10-30 degrees to the cell axis. Because of that volume and alignment, the S2 layer largely determines longitudinal stiffness, strength and longitudinal shrinkage.

Question 6Wood science: timber structure, growth, seasoning and moisture behaviour

For normal clear wood dried from green to oven-dry, which order of shrinkage is correct, from greatest to least?

  1. Tangential, then longitudinal, then radial
  2. Longitudinal, then tangential, then radial
  3. Radial, then tangential, then longitudinal
  4. Tangential, then radial, then longitudinal Correct answer.

Explanation

Shrinkage is greatest across the grain in the tangential direction, typically about 7-8%, less in the radial direction at roughly 4%, and negligible along the grain at well under 1%. Rays and the restraining effect of the ring structure limit radial movement, while tangential movement is comparatively free.

Question 7Wood science: timber structure, growth, seasoning and moisture behaviour

Why is a progressive kiln schedule used for drying thick hardwood boards?

  1. It keeps the kiln temperature low for the whole charge to prevent any darkening of the timber
  2. It holds a constant wet-bulb depression so that the surface and the core dry at the same rate throughout
  3. It begins with mild, humid air and raises the drying potential gradually, limiting checking and case-hardening Correct answer.
  4. It raises the relative humidity step by step so that moisture leaves the core faster than the surface

Explanation

A progressive schedule starts humid and relatively cool so the surface does not dry far ahead of the core, then increases the wet-bulb depression as the charge loses moisture. Keeping the moisture gradient, and therefore the surface tensile stress, within safe limits avoids checking, collapse and case-hardening in thick stock.

Question 8Wood science: timber structure, growth, seasoning and moisture behaviour

Which combination of features is typical of juvenile wood close to the pith of a fast-grown conifer?

  1. High density, small microfibril angle and low longitudinal shrinkage
  2. Low density, short tracheids and a large microfibril angle, giving high longitudinal shrinkage Correct answer.
  3. Thick cell walls, long tracheids and a low lignin content
  4. Uniform density with a large microfibril angle and no extractives present

Explanation

Juvenile wood is formed in the first ten to twenty rings from the pith, where tracheids are short, walls thin, density low and the S2 microfibril angle large. That combination gives low stiffness and unusually high longitudinal shrinkage, so juvenile wood distorts more than mature wood during drying.

Question 9Wood science: timber structure, growth, seasoning and moisture behaviour

Which stress pattern defines case-hardening in a kiln-dried board?

  1. Uniform compression throughout the section, caused by rapid cooling of the charge after drying
  2. Surface layers in tension and the core in compression, because the surface set while the core was still wet Correct answer.
  3. Uniform tension throughout the section, caused by the weight of the drying stack pressing on the boards
  4. Surface layers in compression and the core in tension, because the core dried ahead of the surface

Explanation

Case-hardening develops when the outer layers dry below the fibre saturation point and set in a shrunken state while the core remains wet and swollen. Once moisture is equalised, the set case is held in tension and the core in compression, and the locked-in stresses persist until relieved by a conditioning treatment.

Question 10Wood science: timber structure, growth, seasoning and moisture behaviour

How does moisture move through a board being dried above and below the fibre saturation point?

  1. Moisture moves by bulk flow through the lumens in both ranges, driven by capillary pressure alone
  2. Moisture moves only as vapour in both ranges, driven by differences in total air pressure across the board
  3. Free water moves by capillarity and vapour flow above fibre saturation, while below it bound water diffuses through the cell walls Correct answer.
  4. Bound water diffuses through the cell walls above fibre saturation, and free water moves by capillarity below it

Explanation

Above the fibre saturation point the lumens still hold free water, which is drawn through pit membrane openings by capillary forces and can also travel as vapour, so the wood's permeability governs the rate. Once the lumens are empty, the remaining bound water must diffuse through the cell wall along the moisture gradient, which is a far slower process and controls the later stages of drying.

Question 11Wood science: timber structure, growth, seasoning and moisture behaviour

In a stem of a typical hardwood such as oak, which anatomical feature is present that is absent from a softwood such as pine?

  1. Ray parenchyma cells
  2. Vessels (pores) in the earlywood Correct answer.
  3. Tracheids with bordered pits
  4. Resin canals in the xylem

Explanation

Hardwoods contain vessel elements, which appear as pores in cross-section; softwoods lack vessels and rely mainly on tracheids for conduction and support. Bordered pits and ray parenchyma occur in both groups, and resin canals are characteristic of many softwoods.

Question 12Wood science: timber structure, growth, seasoning and moisture behaviour

Which tissue in the inner bark of a tree translocates sugars produced in the crown?

  1. Sieve elements of the phloem Correct answer.
  2. Ray parenchyma in the heartwood
  3. Tracheids of the xylem
  4. Cork cambium

Explanation

Sieve elements in the inner bark, or phloem, conduct sugars and other assimilates from the leaves to growing and storage tissues. The cork cambium produces corky outer bark, while xylem tracheids conduct water and minerals upward.

Question 13Wood science: timber structure, growth, seasoning and moisture behaviour

Which expression correctly gives wood moisture content on the oven-dry basis?

  1. (Wet mass minus oven-dry mass) divided by oven-dry mass, multiplied by 100 Correct answer.
  2. Oven-dry mass divided by wet mass, multiplied by 100
  3. (Wet mass minus oven-dry mass) divided by wet mass, multiplied by 100
  4. Wet mass divided by oven-dry mass, multiplied by 100

Explanation

Moisture content on the oven-dry basis is the mass of water divided by the oven-dry mass, multiplied by 100. The mass of water is wet mass minus oven-dry mass, so dividing by wet mass or using dry mass over wet mass gives the wrong ratio.

Question 14Wood science: timber structure, growth, seasoning and moisture behaviour

In a ring-porous hardwood such as ash, what is the characteristic arrangement of vessels within a growth ring?

  1. Pores of similar size spread evenly through the ring
  2. Tracheids only, with no vessels at all
  3. Pores confined to the latewood only
  4. Large earlywood pores in a distinct band Correct answer.

Explanation

Ring-porous hardwoods form a band of large-diameter vessels in the earlywood, giving a ring of visible pores, followed by much smaller latewood vessels. Diffuse-porous hardwoods, by contrast, have vessels of similar size distributed fairly evenly through the ring.

Question 15Wood science: timber structure, growth, seasoning and moisture behaviour

At a constant temperature, what happens to the equilibrium moisture content of wood as relative humidity increases from 40% to 80%?

  1. It rises only after free water appears in the lumens
  2. It increases, following a sorption isotherm Correct answer.
  3. It remains constant until the fibre saturation point
  4. It decreases because humid air holds less water

Explanation

At constant temperature, equilibrium moisture content rises with relative humidity because more water vapour is available to be adsorbed onto cell-wall sites. The relationship is described by a sorption isotherm and is not a step change at the fibre saturation point.

Question 16Wood science: timber structure, growth, seasoning and moisture behaviour

In a kiln schedule, the wet-bulb depression is the difference between the dry-bulb and wet-bulb temperatures. What does a larger depression indicate about the drying conditions?

  1. Lower relative humidity and greater drying potential Correct answer.
  2. Saturated air and risk of re-wetting the load
  3. Higher equilibrium moisture content and slower drying
  4. A wet-bulb temperature above the dry-bulb temperature

Explanation

A larger wet-bulb depression means the wet bulb is cooled more by evaporation, which indicates lower relative humidity and a stronger driving force for drying. A small depression means humid air and a milder schedule.

Question 17Wood science: timber structure, growth, seasoning and moisture behaviour

A green board has a tangential dimension of 200 mm and measures 184 mm when oven-dry. What is its tangential shrinkage expressed as a percentage of the green dimension?

  1. 7.5%
  2. 8% Correct answer.
  3. 6%
  4. 16%

Explanation

Shrinkage percentage is calculated from the change in dimension divided by the green dimension, multiplied by 100: (200 - 184) / 200 × 100 = 8%. Using the oven-dry dimension as the denominator would give a different, incorrect value.

Question 18Wood science: timber structure, growth, seasoning and moisture behaviour

For clear wood at a given moisture content, which feature of the growth rings most directly raises density in a softwood?

  1. A greater proportion of thick-walled latewood Correct answer.
  2. A larger pith diameter
  3. A greater proportion of wide earlywood tracheids
  4. More numerous resin canals

Explanation

Latewood tracheids have thicker walls and smaller lumens than earlywood tracheids, so a higher latewood proportion increases the mass of cell-wall material per unit volume and therefore density. Resin canals and pith size have little direct effect on clear-wood density.

Question 19Wood science: timber structure, growth, seasoning and moisture behaviour

In the vascular cambium, what is the effect of a periclinal division compared with an anticlinal division?

  1. Periclinal produces bark; anticlinal produces xylem
  2. Periclinal adds to a radial file; anticlinal adds a circumferential file Correct answer.
  3. Periclinal occurs only in hardwoods; anticlinal only in softwoods
  4. Periclinal adds a circumferential file; anticlinal adds a radial file

Explanation

Periclinal, or tangential, divisions of cambial initials add cells within an existing radial file and thus increase stem diameter. Anticlinal divisions add new initial cells around the circumference, allowing the cambial cylinder to expand laterally.

Question 20Wood science: timber structure, growth, seasoning and moisture behaviour

A wood specimen is brought to equilibrium at 65% relative humidity, first by adsorption from oven-dry and then by desorption from a wet state. What is the expected result?

  1. The desorption moisture content is higher than the adsorption moisture content Correct answer.
  2. The adsorption moisture content is higher because dry wood absorbs quickly
  3. Both paths give identical moisture content
  4. Hysteresis affects only temperatures above 100°C

Explanation

Wood shows sorption hysteresis: at the same relative humidity, equilibrium moisture content is higher when reached by desorption from a wetter state than by adsorption from a drier state. This is a cell-wall phenomenon and does not require temperatures above 100°C.

Question 21Wood science: timber structure, growth, seasoning and moisture behaviour

For most timbers, the fibre saturation point corresponds to a moisture content of approximately:

  1. 8–12%
  2. 28–30% Correct answer.
  3. 45–55%
  4. 18–22%

Explanation

The fibre saturation point is the moisture content at which the cell walls are saturated with bound water but the lumens contain no free water. For most woods this occurs at about 28–30% moisture content.

Question 22Wood science: timber structure, growth, seasoning and moisture behaviour

Which tissue conducts water and dissolved mineral nutrients from the roots to the crown of a living tree?

  1. Vascular cambium
  2. Cork cambium
  3. Phloem
  4. Xylem Correct answer.

Explanation

Xylem, principally the sapwood, contains tracheids and/or vessels that conduct the transpiration stream upward from the roots. Phloem transports sugars, while the cambia produce new cells.

Question 23Wood science: timber structure, growth, seasoning and moisture behaviour

In an outdoor air-drying stack of green boards, what is the main purpose of placing stickers between the layers?

  1. To sterilise the wood against insects
  2. To allow air to circulate over the board surfaces Correct answer.
  3. To increase the weight on the stack
  4. To prevent the boards from shrinking

Explanation

Stickers are thin spacers that create horizontal air channels so air can pass over the faces and carry moisture away. Without them the inner boards dry very slowly and are prone to stain and decay.

Question 24Wood science: timber structure, growth, seasoning and moisture behaviour

For clear wood at the same moisture content, why is tangential shrinkage usually greater than radial shrinkage?

  1. Radial shrinkage is caused solely by loss of free water
  2. Tangential cell walls contain more lignin than radial walls
  3. Tangential shrinkage occurs only above fibre saturation
  4. Rays restrain radial shrinkage more than tangential shrinkage Correct answer.

Explanation

Across the grain, rays and the radial arrangement of cell walls restrain radial shrinkage, so tangential shrinkage is larger. The usual order is tangential > radial > longitudinal.

Question 25Wood science: timber structure, growth, seasoning and moisture behaviour

Which wood component is the most hygroscopic of the main cell-wall polymers and largely governs moisture sorption?

  1. Cellulose
  2. Lignin
  3. Extractives
  4. Hemicellulose Correct answer.

Explanation

Hemicellulose is amorphous and has abundant accessible hydroxyl groups, so it sorbs water readily and is the most hygroscopic of the main cell-wall polymers. Cellulose also sorbs water, but much of it is crystalline and less accessible; lignin is relatively hydrophobic.

Question 26Wood science: timber structure, growth, seasoning and moisture behaviour

In a softwood tracheid, what is the main function of the bordered pits on the radial walls?

  1. They conduct sugars downward through the inner bark
  2. They permit water flow between adjacent tracheids Correct answer.
  3. They provide the main longitudinal reinforcement to the stem
  4. They store starch reserves for the living tree

Explanation

Bordered pits form valved openings in the tracheid wall, allowing water to move between tracheids in the living tree. In dried wood the pit membrane often aspirates against the border, which sharply reduces permeability.

Question 27Wood science: timber structure, growth, seasoning and moisture behaviour

What is the most common cause of surface checking during kiln drying?

  1. Rapid surface drying below fibre saturation Correct answer.
  2. Drying at a temperature below 0 °C
  3. Storing green boards under water
  4. Using a very small wet-bulb depression

Explanation

When the surface dries below fibre saturation before the core, the surface layer tries to shrink but is held by the wet core, generating tensile stress. If the stress exceeds the transverse strength, surface checks open.

Question 28Wood science: timber structure, growth, seasoning and moisture behaviour

At a constant relative humidity, what happens to the equilibrium moisture content of wood as the temperature is raised?

  1. It decreases Correct answer.
  2. It increases
  3. It first increases and then becomes zero
  4. It stays exactly the same

Explanation

At fixed relative humidity, raising the temperature increases the saturation vapour pressure, so wood equilibrates at a lower moisture content. Kiln operators use this effect when raising temperature during drying.

Question 29Wood science: timber structure, growth, seasoning and moisture behaviour

A lumber board sawn from a tree with strong spiral grain is most likely to show which behaviour after drying and machining?

  1. It will remain straight but turn much darker
  2. It will become much more resistant to decay
  3. It will shrink equally in every direction
  4. It will twist and lose strength Correct answer.

Explanation

Spiral grain means fibres are inclined to the axis of the tree, so a sawn board contains fibres running diagonally. On drying and machining, this geometry produces twist and reduces tensile strength parallel to the board axis.

Question 30Wood science: timber structure, growth, seasoning and moisture behaviour

Which drying condition most directly promotes honeycombing in thick hardwood boards?

  1. Rapid drying that creates a steep moisture gradient Correct answer.
  2. Rewetting the board after it has reached equilibrium
  3. A very slow kiln schedule with a small wet-bulb depression
  4. Air drying under a tarpaulin with no stickers

Explanation

Honeycombing is internal cracking caused by tensile stress in the core when the shell has set and the core is still wet and shrinking. Rapid drying of thick boards steepens the moisture gradient and raises that internal stress.

Question 31Timber identification, classification, defects and material selection

In softwoods such as pine and spruce, which cell type carries out both water conduction and mechanical support?

  1. Epithelial cells lining resin canals
  2. Vessel elements
  3. Ray parenchyma
  4. Tracheids Correct answer.

Explanation

Softwoods are built almost entirely of tracheids, elongated thick-walled cells that both conduct water upward and give the stem its strength. They contain no vessel elements, and rays make up only a small fraction of the volume.

Question 32Timber identification, classification, defects and material selection

Which term describes a knot formed by a branch that died while the tree was still growing, so that later wood was laid down around the dead stub without being bonded to it?

  1. Spike knot
  2. Cluster knot
  3. Live (intergrown) knot
  4. Dead (encased) knot Correct answer.

Explanation

When a branch dies, the tree keeps adding wood around the dead stub but no longer grows wood continuous with it. The resulting dead or encased knot is not bonded to the surrounding timber, so it can loosen or fall out and is graded as a strength-reducing defect.

Question 33Timber identification, classification, defects and material selection

In a naturally durable species such as western red cedar, which part of the stem gives the timber its resistance to decay and insect attack?

  1. Sapwood
  2. Heartwood Correct answer.
  3. Inner bark
  4. Cambium

Explanation

Durability in species such as western red cedar, teak and iroko comes from extractives deposited in the heartwood as the inner cells die and stop conducting. Sapwood is living tissue that stores starch and conducts sap, so it is readily attacked and should not be specified where there is a decay hazard.

Question 34Timber identification, classification, defects and material selection

A hardwood sample shows a distinct band of large pores in the earlywood and much smaller pores in the latewood. How is this wood classified?

  1. Ring-porous Correct answer.
  2. Diffuse-porous
  3. Semi-ring-porous
  4. Non-porous softwood

Explanation

Ring-porous hardwoods such as oak and ash form a band of wide earlywood vessels in spring followed by dense latewood with much smaller pores, giving an abrupt change in pore size. Diffuse-porous woods have evenly spread pores of similar size, and semi-ring-porous woods show a gradual transition rather than a distinct band.

Question 35Timber identification, classification, defects and material selection

On the lower side of a leaning softwood stem, the tree lays down wood that is darker, denser and richer in lignin, and that shrinks far more than normal along the grain. What is this wood called?

  1. Brittle heart
  2. Juvenile wood
  3. Tension wood
  4. Compression wood Correct answer.

Explanation

Compression wood forms on the lower side of leaning or bent softwood stems and pushes the stem back upright. Its high lignin content and excessive longitudinal shrinkage cause bowing and distortion after sawing; tension wood is the equivalent tissue in hardwoods and forms on the upper side.

Question 36Timber identification, classification, defects and material selection

A separation running along the grain between growth rings, often found near the pith in the butt of a mature tree, is known as which defect?

  1. Surface check
  2. Collapse
  3. Honeycombing
  4. Ring shake Correct answer.

Explanation

Ring shake is a separation along the grain that follows the boundary between growth rings and often stays hidden until the end grain is inspected. Surface checks are drying separations that open from the face, while honeycombing is internal checking caused by drying stresses.

Question 37Timber identification, classification, defects and material selection

Timber attacked by a brown-rot fungus typically shows which pattern of decay?

  1. Pale, fibrous residue where lignin is removed first
  2. White, spongy residue with little loss of strength
  3. Dark blue-black staining with no loss of section
  4. Brown, brittle wood that cracks into cubes Correct answer.

Explanation

Brown-rot fungi break down the cellulose and hemicellulose and leave the lignin, so the wood darkens and splits into cubical pieces, and strength falls sharply even before the decay is obvious. White rots remove lignin as well as cellulose and leave a pale, fibrous, spongy residue.

Question 38Timber identification, classification, defects and material selection

An outdoor deck bearer must carry load and stay wet for long periods. Which material is the most appropriate selection?

  1. Mixed sapwood selected by colour alone
  2. Heartwood of a non-durable species, free of knots
  3. Sapwood of a durable species with widely spaced knots
  4. Straight-grained heartwood of a durable species Correct answer.

Explanation

Decay resistance is concentrated in the heartwood of durable species, so exposed structural members should come from straight-grained heartwood with small, sound knots. Sapwood of even a durable species has little resistance, and large knots or sloping grain reduce strength.

Question 39Timber identification, classification, defects and material selection

Internal cracks that open in the core of timber after kiln drying, because a case-hardened shell is in tension while the core is still in compression, are known as which defect?

  1. Spring
  2. Honeycombing Correct answer.
  3. Surface checking
  4. Cupping

Explanation

Rapid drying sets the outer shell in tension while the wet core remains in compression. If the core is weak, or the stresses are released when the piece is re-sawn, internal cracks called honeycombing open up and may stay invisible until the timber is cut.

Question 40Timber identification, classification, defects and material selection

Timber in a heated building held at about 20 °C and 65% relative humidity will settle at approximately which moisture content?

  1. 8%
  2. 6%
  3. 20%
  4. 12% Correct answer.

Explanation

Wood is hygroscopic and reaches an equilibrium moisture content that depends on the temperature and humidity of the surrounding air. At 20 °C and 65% relative humidity, a typical condition for heated interiors, the equilibrium moisture content is about 12%, the value used for interior joinery design.

Question 41Timber identification, classification, defects and material selection

Which statement correctly distinguishes hardwoods from softwoods in timber classification?

  1. Hardwoods come only from tropical trees, while softwoods come only from temperate trees.
  2. Hardwoods are angiosperms whose seeds are enclosed in an ovary, while softwoods are gymnosperms with naked seeds. Correct answer.
  3. Hardwoods are always denser than softwoods, while softwoods are always lighter.
  4. Hardwoods lack vessels, while softwoods contain vessels for water conduction.

Explanation

The hardwood/softwood division is botanical: hardwoods are flowering plants (angiosperms) and softwoods are conifers (gymnosperms). Density and geography vary widely within both groups, so neither is a reliable classifier. Hardwoods generally contain vessels, while softwoods conduct water mainly through tracheids.

Question 42Timber identification, classification, defects and material selection

In a freshly felled tree, which part of the stem is the light-coloured, sap-conducting zone that is generally less durable than the inner wood?

  1. Pith
  2. Inner bark
  3. Heartwood
  4. Sapwood Correct answer.

Explanation

Sapwood is the outer wood zone that conducts water and stores starch in the living tree. It lacks the extractive deposits that make heartwood more durable, so it is more susceptible to decay and insects. The pith is the small central core, and inner bark is phloem rather than wood.

Question 43Timber identification, classification, defects and material selection

A lengthwise separation of timber fibres along the grain, confined mainly to the end grain and caused by drying stresses, is called a:

  1. shake
  2. check Correct answer.
  3. knot
  4. waney edge

Explanation

A check is a drying crack that runs along the grain and commonly appears at the end grain as moisture leaves faster from the ends. It is distinct from a shake, which is a separation between growth rings or through the pith. Knots are branch bases, and wane is bark or rounded surface left on an edge.

Question 44Timber identification, classification, defects and material selection

Which statement about shrinkage of normal wood as it dries from green to oven-dry is correct?

  1. Radial shrinkage is greatest, followed by tangential, then longitudinal.
  2. Tangential shrinkage is greatest, followed by radial, then longitudinal. Correct answer.
  3. Shrinkage is approximately equal in all three directions.
  4. Longitudinal shrinkage is greatest, followed by radial, then tangential.

Explanation

Wood shrinks most across the growth rings (tangentially) and less in the radial direction, while longitudinal shrinkage is normally very small. This anisotropy is why boards distort and why grain orientation matters in material selection. The typical order is tangential greater than radial greater than longitudinal.

Question 45Timber identification, classification, defects and material selection

In a leaning hardwood stem, the wood formed on the upper side that can cause bowing and excessive longitudinal shrinkage after drying is:

  1. compression wood, recognised by dark colour and high lignin content
  2. heartwood, recognised by darker colour and extractive deposits
  3. juvenile wood, recognised by wider growth rings and lower density
  4. tension wood, recognised by a gelatinous fibre layer and associated with high longitudinal shrinkage Correct answer.

Explanation

Hardwoods form tension wood on the upper side of a lean; its gelatinous fibres are rich in cellulose and can shrink strongly along the grain. That longitudinal shrinkage is a common cause of bowing after sawing or drying. Compression wood is the equivalent reaction wood in softwoods and forms on the lower side.

Question 46Timber identification, classification, defects and material selection

Oak flooring is to be fixed with metal fasteners in a humid coastal building. Which fastener material is most appropriate?

  1. Galvanised steel, because the zinc coating is unaffected by timber extractives
  2. Stainless steel, because oak contains acids and tannins that corrode ferrous metals Correct answer.
  3. Mild steel, because it is strong and cheap
  4. Aluminium, because it is light and does not react with timber

Explanation

Oak contains acids and tannins that attack mild steel and can stain the timber, especially in damp conditions. Stainless steel is the usual specification where corrosion resistance and a long service life are required. Galvanising offers only limited protection and can be consumed at cut edges or in wet service.

Question 47Timber identification, classification, defects and material selection

A pale softwood sample shows distinct resin canals when a clean end-grain surface is examined with a hand lens. Which identification conclusion is best supported?

  1. The sample is likely to be a true fir or hemlock because both contain resin canals.
  2. The sample is likely to be pine, spruce, larch or Douglas fir because these softwoods normally contain resin canals. Correct answer.
  3. The sample cannot be identified further because resin canals occur in all softwoods.
  4. The sample must be a hardwood because resin canals occur only in angiosperms.

Explanation

Resin canals are a useful softwood identification feature, and several common genera such as pine, spruce, larch and Douglas fir normally possess them. True firs, hemlocks and many cedars generally lack normal resin canals, so their presence is a positive clue. Resin canals do not occur in hardwoods, which have vessels instead.

Question 48Timber identification, classification, defects and material selection

Compared with a flat-sawn board from the same log, a quarter-sawn board is generally:

  1. more prone to cupping and has greater width shrinkage
  2. more dimensionally stable across its width and less prone to cupping Correct answer.
  3. cut with growth rings parallel to the wide face and is less stable
  4. always stronger in bending because the grain runs at 90° to the span

Explanation

Quarter-sawing brings the growth rings at a high angle to the wide face, so width movement is dominated by the smaller radial shrinkage rather than the larger tangential shrinkage. The result is a board that is more stable across its width and less likely to cup. Quarter-sawn stock usually costs more because it produces narrower boards and more waste.

Question 49Timber identification, classification, defects and material selection

A piece of timber shows a lens-shaped pocket of corky bark enclosed within otherwise sound wood. This defect is best described as:

  1. a heart shake
  2. an ingrown bark pocket Correct answer.
  3. a resin pocket
  4. a live knot

Explanation

An ingrown bark pocket forms when a wound closes over bark, enclosing it inside later wood growth. It is a strength-reducing defect and can also trap moisture and encourage decay. A knot is branch wood, a heart shake is a radial separation near the pith, and a resin pocket contains resin rather than bark.

Question 50Timber identification, classification, defects and material selection

A softwood pole dries with a pronounced twist along its length, and the grain on the surface runs diagonally rather than parallel to the axis. Which defect and effect does this indicate?

  1. Ring shake, which separates the pole into concentric shells.
  2. Compression wood, which causes the pole to swell longitudinally.
  3. Spiral grain, which causes twisting on drying and reduces tensile strength. Correct answer.
  4. Case-hardening, which produces a hardened shell and a weak core.

Explanation

Spiral grain is a helical arrangement of fibres around the stem axis; the diagonal surface grain is the visible clue. On drying, the helical shrinkage pattern makes the pole twist, and the inclined fibres reduce tensile and bending strength. Compression wood, ring shake and case-hardening produce different visible features and effects.