← Construction Technology, Equipment, Planning & Management · AAI Manager (Civil)

Chapter 1 of 9

Engineering Materials

In the AAI Manager (Civil) syllabus under Construction Technology, Equipment, Planning & Management · 4 parts

Building Stones · Bricks, Tiles & Clay Products · Building Lime · Timber & Wood Products

CIVILGYAN TEST SERIES · civilgyantests.com — free study notes for civil engineering exams

📑 Contents (49 sections)

Part 1 of 4

Building Stones

Last reviewed 16 Sept 2026 · 9 min read

Classification of rocks

Geological classification

Type	Formation	Examples
Igneous rocks	Cooling and solidification of molten magma — intrusive (plutonic), coarse-grained (cooled slowly deep inside) or extrusive (volcanic), fine-grained (cooled quickly at the surface)	Granite (plutonic), basalt and trap (volcanic), dolerite (hypabyssal), syenite, diorite
Sedimentary rocks	Deposition and consolidation of sediments by water, wind or ice — usually stratified	Sandstone, limestone, shale, laterite, conglomerate, gypsum
Metamorphic rocks	Alteration of igneous or sedimentary rocks by heat and pressure	Marble (from limestone), quartzite (from sandstone), slate (from shale), gneiss (from granite), schist

Physical classification

Stratified rocks — in layers (sedimentary rocks such as sandstone, limestone); can be split along bedding planes.
Unstratified rocks — no layers; compact crystalline structure (igneous rocks such as granite, trap).
Foliated rocks — tend to split along a definite direction (metamorphic rocks such as slate, gneiss, schist).

Chemical classification

Class	Main constituent	Examples	Remarks
Siliceous	Silica (SiO₂)	Granite, quartzite, sandstone (silica-cemented)	Hard, durable, resist weathering
Argillaceous	Clay (alumina)	Slate, laterite, shale	Dense and compact or soft and brittle depending on type
Calcareous	Calcium carbonate	Limestone, marble	Affected by acids and polluted (industrial) atmospheres

Common building stones and uses

Stone	Characteristics	Uses
Granite	Igneous, hard, strong, durable, takes a good polish; high crushing strength; poor fire resistance (cracks on heating)	Bridge piers, docks, retaining walls, steps, kerbs, facing, flooring, road aggregate
Basalt and trap	Igneous, hard, tough, dark, difficult to dress	Road metal, rubble masonry, railway ballast, aggregates
Sandstone	Sedimentary, stratified, porous; strength depends on cementing material (siliceous best)	Walling, ashlar work, flooring, ornamental work
Limestone	Sedimentary, calcareous; varieties include compact and oolitic	Flooring, walling, manufacture of lime and cement, road metal (hard varieties)
Marble	Metamorphic, crystalline, takes a high polish, variety of colours	Flooring, facing, decorative and ornamental work, statues
Slate	Metamorphic, splits into thin non-absorbent sheets	Roofing, damp-proof courses, sills, cisterns
Quartzite	Metamorphic, very hard, durable, difficult to work	Rubble masonry, road metal, concrete aggregate
Gneiss	Metamorphic, banded, strong	Street paving, rough stone work
Laterite	Residual (weathered) rock rich in iron and aluminium oxides; soft when quarried, hardens on exposure	Building blocks in coastal areas (e.g. Kerala, Konkan), road metal
Kankar	Impure limestone nodules	Lime manufacture, road metal for low-traffic roads

Qualities of a good building stone

Crushing strength — adequate for loads; good structural stones commonly have high strength (e.g. granite and trap rank highest; many sandstones and limestones are lower).
Appearance — uniform colour and texture for face work; free from clay holes, spots and cracks.
Durability — resistance to weathering (rain, frost, wind, temperature changes, chemicals).
Hardness — resistance to abrasion (important for floors, pavements, steps); measured by Mohs' scale.
Toughness — resistance to impact (road metal).
Low porosity and water absorption — porous stones absorb water and deteriorate by frost and chemical action (water absorption for good stones is low, commonly below about 5%).
Specific gravity — heavier stones (specific gravity above about 2.7) are generally more compact and durable, suited to dams and retaining walls.
Fire resistance — stones with minerals of different expansion (e.g. granite with quartz) crack in fire; argillaceous stones resist fire better.
Workability and dressing — ease of cutting and dressing (economy).
Texture — fine, compact, crystalline structure is desirable.
Seasoning — freshly quarried stones contain quarry sap and should be seasoned (allowed to dry) before use, commonly for several months.
Availability and cost.

Tests on stones

Test	Purpose / procedure
Crushing strength test	Cube specimens tested in a compression testing machine; strength = failure load ÷ area
Water absorption test	Dry specimen immersed in water (24 hours or boiling); absorption $= \frac{W _{2} - W _{1}}{W _{1}} \times 100$
Specific gravity	$G = \frac{W _{1}}{W _{1} - W _{3}}$ ( $W_{1}$ dry weight, $W_{3}$ weight in water) — heavier stones more compact
Hardness test (Mohs' scale)	Scratching with minerals of known hardness; also Dorry's abrasion test
Impact (toughness) test	Resistance to repeated blows of a hammer (as in aggregate impact tests)
Attrition (Deval) test	Rate of wear of stone pieces rotated in a cylinder — for road stones
Acid test	Stone immersed in dilute hydrochloric (or sulphuric) acid — sharp edges and firm grains indicate resistance to acidic atmospheres; calcareous stones effervesce
Crystalline test	Microscopic examination of crystals
Freezing and thawing (frost) test	Repeated cycles in a freezing mixture — weathering resistance; Brard's test uses sodium sulphate crystallisation
Smith's test	Stone chips shaken in water — clear water indicates absence of soluble or earthy matter

Mohs' scale of hardness

Hardness	Mineral	Hardness	Mineral
1	Talc	6	Orthoclase (feldspar)
2	Gypsum	7	Quartz
3	Calcite	8	Topaz
4	Fluorite	9	Corundum
5	Apatite	10	Diamond

Part 2 of 4

Bricks, Tiles & Clay Products

Last reviewed 16 Sept 2026 · 10 min read

Brick earth

Composition of good brick earth

Constituent	Proportion (approx.)	Role
Alumina (clay)	20–30%	Gives plasticity for moulding; excess causes shrinkage, warping and cracking on drying and burning
Silica	50–60%	Prevents cracking, shrinkage and warping; gives uniform shape and durability; excess makes bricks brittle
Lime	Less than about 5%	In fine powder, reduces shrinkage and helps silica to fuse slightly (binding); excess causes melting and loss of shape; lumps of lime cause splitting
Magnesia	Less than about 1%	Gives a yellow tint; reduces shrinkage; excess causes decay
Iron oxide	About 5–6%	Gives red colour and helps fusion; improves strength and impermeability

Harmful ingredients

Lime lumps — expand on slaking after burning, causing bricks to split (lime bursting).
Iron pyrites — cause crystallisation, discolouration and splitting.
Alkalis (salts of sodium, potassium) — cause efflorescence (white patches) and melting.
Pebbles and gravel — prevent uniform mixing and weaken bricks.
Organic matter and vegetation — leave pores after burning, making bricks porous.

Manufacture of bricks

1. Preparation of clay

Unsoiling (removal of top soil), digging, cleaning (removing stones, roots), weathering (exposure to atmosphere to soften and mature the clay), blending (mixing ingredients) and tempering (mixing with water and kneading — in a pug mill for large-scale production) to obtain a homogeneous plastic mass.

2. Moulding

Method	Description
Hand moulding — ground moulding	Moulds filled on levelled ground; bricks left on the ground
Hand moulding — table moulding	Moulding on a table; bricks carried to drying area
Slop moulding	Mould dipped in water before filling — smooth surface
Sand moulding	Mould sprinkled with sand — prevents sticking
Machine moulding — plastic clay (wire-cut) method	Clay extruded as a column and cut by wires — uniform, many bricks
Machine moulding — dry press method	Nearly dry clay pressed in moulds under high pressure — dense, accurate bricks

A frog — a shallow depression on one face of a hand-moulded brick — provides a key for mortar, reduces weight and may carry the manufacturer's mark. Bricks with frogs are laid frog upward.

3. Drying

Green bricks are dried (naturally in the shade/open air, or artificially in drying chambers) to reduce moisture before burning, preventing cracks and distortion. Natural drying commonly takes one to two weeks depending on weather.

4. Burning

Burning gives strength, hardness and durability through dehydration and partial vitrification of clay; bricks are commonly burnt at around 900–1100 °C.

Kiln / clamp	Type	Features
Clamp	Intermittent, temporary	Bricks and fuel stacked in alternate layers and burnt; cheap, but uneven burning, many under- and over-burnt bricks
Intermittent kilns (e.g. Scotch kiln)	Loaded, fired, cooled and unloaded batch by batch	Better control than clamps; fuel waste in reheating
Bull's trench kiln (BTK)	Continuous, trench in ground (circular or oval); fire moves round the trench	Widely used in India; large output; traditional fixed-chimney kilns cause air pollution
Zigzag kiln	Continuous, air flows in a zigzag path through the bricks	Better fuel efficiency and lower emissions — promoted as an improvement over conventional BTKs
Hoffman's kiln	Continuous, permanent (circular, with chambers and roof)	Burning even in rain; good-quality bricks; high initial cost
Tunnel kiln	Continuous; bricks on cars move through a tunnel with fixed preheating, firing and cooling zones	High quality and output; mechanised factories

Sizes of bricks

Brick	Size (mm)
Modular (IS) brick	190 × 90 × 90 (nominal with 10 mm mortar joint: 200 × 100 × 100)
Modular brick (thinner variant)	190 × 90 × 40
Conventional (traditional) brick	About 230 × 110 × 70 (9″ × 4½″ × 3″)

For modular bricks, about 500 bricks make one cubic metre of masonry (including mortar joints).

Classification of bricks

Traditional (field) classification

Class	Description	Use
First-class bricks	Table-moulded, well burnt in kilns, uniform red colour, sharp edges, metallic ringing sound, no scratch with finger nail, low water absorption	Exposed masonry, important structures
Second-class bricks	Ground-moulded, kiln burnt, slightly irregular shape or colour, fine cracks	Plastered masonry
Third-class bricks	Ground-moulded, burnt in clamps, soft, light-red, dull sound	Temporary structures, sheltered areas
Fourth-class (over-burnt) bricks — jhama	Over-burnt, distorted, very hard, dark	Broken as aggregate (brick ballast) for foundations, floors, lime concrete
Under-burnt bricks	Soft, yellowish, absorbent	Not used for masonry

IS classification (IS 1077)

Common burnt clay bricks are classified by average compressive strength into classes (designations in N/mm²) such as 35, 30, 25, 20, 17.5, 15, 12.5, 10, 7.5, 5 and 3.5 — the class designation is the minimum average compressive strength.

Tests on bricks

Laboratory tests (IS 3495)

Test	Procedure / requirement
Compressive strength	Frog filled with mortar, specimens immersed in water, capped and tested; strength = load ÷ bed area
Water absorption	Dry bricks immersed in cold water for 24 hours (or boiled for 5 hours); absorption = (wet − dry)/dry × 100; for common bricks it should generally not exceed about 20% by weight for lower classes (lower limits for higher classes)
Efflorescence	Bricks placed on end in distilled water in a dish until water is absorbed and evaporated; deposit of white salts rated as nil, slight (up to about 10% of exposed area covered by a thin deposit), moderate (about 10–50%), heavy (more than 50%) and serious (heavy deposit with powdering/flaking)
Dimensional tolerance	Twenty bricks placed in contact in a row along length, width and height; total dimensions must be within specified limits
Warpage	Measurement of distortion of faces

Field tests

Sound test — two bricks struck together should give a clear metallic ringing sound.
Hardness test — no impression when scratched with a finger nail.
Soundness/strength test — a good brick should not break when dropped flat on hard ground from a height of about 1 m.
Shape, size and colour — uniform, with sharp straight edges and uniform colour.
Structure — a broken brick shows a homogeneous, compact structure without holes or lumps.

Part 3 of 4

Building Lime

Last reviewed 16 Sept 2026 · 8 min read

Lime in construction

Lime was the principal binding material before Portland cement and remains useful in mortars, plasters, whitewash, soil stabilisation and restoration of heritage buildings.

Sources: limestone, chalk, kankar (impure nodular limestone), shells (sea shells), dolomite (for magnesian lime).

Terms

Term	Meaning
Calcination	Heating limestone to a high temperature (around 900 °C) to drive off CO₂
Quicklime (caustic lime)	Calcium oxide (CaO) obtained by calcination — white, amorphous, very reactive with water
Slaking	Chemical combination of quicklime with water, with heat, hissing and swelling
Slaked lime (hydrated lime)	Calcium hydroxide Ca(OH)₂ — a fine white powder
Milk of lime	Thin suspension of slaked lime in water — used for whitewash
Lime putty	Thick paste of slaked lime and water — for plaster and mortar
Setting	Hardening of lime — by carbonation (fat lime) or by hydration of silicates and aluminates (hydraulic lime)

Chemistry of lime

FormulaReactions

Calcination:

C a C O_{3} \approx 900 ° C C a O + C O_{2}

Slaking (exothermic, volume increases):

C a O + H_{2} O \to C a (O H)_{2} + heat

Setting by carbonation (slow; needs air):

C a (O H)_{2} + C O_{2} \to C a C O_{3} + H_{2} O

Hydraulic set: clay (silica and alumina) in limestone forms calcium silicates and aluminates on burning, which hydrate and harden like cement, even under water.

Molecular weights: CaCO₃ = 100, CaO = 56, CO₂ = 44, H₂O = 18, Ca(OH)₂ = 74.

Part 4 of 4

Timber & Wood Products

Last reviewed 16 Sept 2026 · 13 min read

Classification of trees

Class	Growth	Examples
Exogenous trees	Grow outward by adding annual rings under the bark — yield useful timber	Softwoods and hardwoods
Endogenous trees	Grow inward; fibrous mass, no annual rings	Bamboo, cane, palm — limited use as timber (bamboo widely used for scaffolding, structures)

Softwoods and hardwoods

Softwoods	Hardwoods
From conifers — needle-like leaves, mostly evergreen	From broad-leaved (deciduous) trees
Distinct annual rings	Annual rings less distinct
Generally light in colour and weight, resinous	Generally darker and heavier, non-resinous
Weaker, easier to work	Stronger, harder, more durable (with exceptions)
Examples: deodar, chir (pine), fir, spruce, kail	Examples: teak, sal, shisham (rosewood), oak, mahogany, babul, mango

Structure of a tree (cross-section)

Part	Description
Pith (medulla)	Innermost central core — dies and decays in old trees
Heartwood	Inner, dead portion — darker, harder, stronger and more durable; gives useful timber
Sapwood	Outer, living portion near the bark — lighter colour, carries sap, less durable, more prone to decay and insects
Cambium layer	Thin layer between sapwood and inner bark — where new wood cells form
Inner bark (bast) and outer bark	Protective coverings
Annual rings	Concentric rings of spring (light) and autumn (dark) wood — one ring per year indicates age
Medullary rays	Thin radial lines from pith towards bark — hold annual rings together, carry sap

Felling of trees

Trees are felled when mature (maturity varies from a few decades to over a century depending on species); immature timber has more sapwood, and over-mature timber may have decay.
Felling in a season when sap is at its minimum is preferred (to reduce decay and speed seasoning) — commonly mid-winter in plains and mid-summer in hilly regions.

Qualities of good timber

Sound (clear ringing sound when struck); uniform colour and straight, close grain; free from defects (knots, shakes, decay, insect attack); adequate strength, hardness, toughness and elasticity; durability against fungi and insects; well seasoned (appropriate moisture content, no warping); heavy for its species (denser timber is stronger); fibrous and not brittle; sweet smell (fresh cut); good workability and ability to hold nails and screws; fire resistance for large sections.

Seasoning of timber

Seasoning is the controlled drying of timber to reduce its moisture content to a level in equilibrium with the atmosphere where it will be used.

Objectives

Reduces shrinkage, warping and cracking in service.
Increases strength, hardness, stiffness and durability (more resistance to decay).
Reduces weight (economical transport).
Makes timber easier to work, paint, glue and treat with preservatives.
Improves resistance to fungi and insects.

Freshly felled (green) timber may contain moisture exceeding its dry weight; well-seasoned timber commonly has about 10–15% moisture content (lower for furniture in dry interiors, somewhat higher for outdoor/structural use).

FormulaMoisture content of timber

M C (%) = \frac{W _{w e t} - W _{d r y}}{W _{d r y}} \times 100

( $W_{d r y}$ = oven-dry weight.) The fibre saturation point (about 25–30%) is the moisture content at which cell cavities are empty but cell walls saturated — shrinkage and strength changes occur only below it.

Methods

Method	Description	Remarks
Natural (air) seasoning	Stacks of timber with spacers (sticks) under a shed, allowing air circulation	Cheap, slow (months to years), no control, possible defects
Water seasoning	Logs immersed in running water (removes sap), then air dried	Reduces sap; timber may lose some strength and elasticity
Kiln seasoning	Drying in kilns with controlled temperature, humidity and air circulation — compartment kilns and progressive kilns	Quick, well-controlled, uniform — most common commercially; costly
Boiling	Boiling/steaming timber — kills fungi and insects, removes sap	Quick; reduces strength and elasticity; costly for large quantities
Chemical (salt) seasoning	Timber treated with hygroscopic salts (e.g. urea) that slow surface drying relative to the interior	Reduces surface checking
Electrical seasoning	High-frequency current heats the timber	Rapid; expensive
Solar kilns	Use solar heat	Low-cost controlled drying

Conversion (sawing) of timber

Conversion is sawing logs into marketable sizes (planks, battens, scantlings).

Method	Features
Ordinary (flat/through-and-through) sawing	Parallel cuts through the log — simple, economical, least waste; boards prone to warping
Quarter sawing	Log quartered, then sawn roughly radially — attractive figure, less warping and shrinkage, more waste
Tangential sawing	Cuts tangential to annual rings — shows grain figure; shrinks more in width
Radial sawing	Cuts along medullary rays — best quality boards, least warping; most wasteful and costly

Defects in timber

Defects due to natural forces

Defect	Description
Knots	Bases of branches embedded in the trunk — live (sound, tight) knots, dead/loose knots (fall out); reduce strength (especially in tension zones)
Shakes	Cracks separating fibres — heart shakes (from the pith, due to shrinkage of heartwood), cup/ring shakes (along annual rings, due to frost or uneven growth), star shakes (from bark inward, due to extreme heat or frost), radial shakes
Twisted fibres (wandering heart)	Fibres twisted spirally due to wind action — difficult to work
Upsets (ruptures)	Crushed fibres due to felling or strong wind
Rind galls	Curved swellings where branches were improperly cut
Burls, callus, foxiness, dote, wind cracks	Other growth irregularities and early decay signs

Defects due to fungi

Dry rot — fungi attack timber in damp, poorly ventilated, warm conditions (e.g. floor boards on damp walls); timber becomes dry, brittle and powdery; can spread through masonry.
Wet rot — decay under alternate wetting and drying (e.g. posts at ground level); timber becomes soft and spongy.
Brown rot, white rot, heart rot, sap stain, blue stain.

Defects due to insects

Termites (white ants) — hollow out timber internally; beetles (powder-post beetles) — reduce sapwood to powder; marine borers (shipworms) — attack timber in sea water.

Defects due to seasoning

Defect	Description
Bow	Curvature along the length in the direction of thickness
Cup	Curvature across the width
Twist (wind)	Spiral distortion along the length
Spring (crook)	Curvature along the length in the plane of the wide face
Checks and splits	Surface cracks (checks) and cracks through thickness at ends (splits) due to rapid drying
Honeycombing	Internal cracks due to case hardening
Case hardening	Outer layers dry and set in a stretched condition while the core is wet — internal stresses
Warp	General distortion

Defects due to conversion

Chip mark, diagonal grain (improper sawing), torn grain (tool action), wane (original rounded surface/bark on the edge of a sawn piece).

Preservation of timber

Objectives: increase durability and life; protect from fungi, insects and marine borers; reduce fire hazard (with fire retardants).

Preservatives

Type	Examples	Remarks
Oil-type	Creosote (coal tar distillate), coal tar	Very effective, especially for outdoor timber (poles, sleepers, piles); dark colour, odour, not paintable
Water-borne (salt) preservatives	Copper–chromium–arsenic (CCA / ASCU), copper–chromium–boron (CCB), zinc chloride, sodium fluoride, boric acid–borax	Clean, odourless, paintable; fixed salts resist leaching (CCA); arsenic-containing preservatives require careful handling
Solvent-type (organic solvent)	Pentachlorophenol (restricted), copper naphthenate, synthetic insecticides in solvents	Good penetration, quick drying

Methods of application

Brushing and spraying — surface treatment; limited penetration; maintenance treatments.
Dipping and steeping — immersion for minutes to days.
Charring — surface burnt to form a protective charcoal layer (e.g. ends of posts in the ground).
Hot and cold open tank process — timber heated in preservative, then cooled so that preservative is drawn in.
Pressure impregnation — in closed cylinders:
- Full-cell (Bethell) process — vacuum then pressure — maximum retention (marine piles).
- Empty-cell processes (Rueping and Lowry) — deep penetration with less retention (economical).
Boucherie process — sap displacement in green poles.

Fire resistance

Timber is combustible, but large sections perform relatively well in fire: the surface chars, and the char layer insulates the inner wood, which retains strength. Fire resistance is improved by fire-retardant chemicals (e.g. ammonium phosphate, ammonium sulphate, borax, boric acid), fire-retardant paints, larger sections, and protection with plaster or boards.

Properties of timber

Anisotropic — properties differ parallel and perpendicular to the grain: compressive and tensile strengths parallel to grain are much higher than perpendicular to grain.
Strength decreases with increasing moisture (below fibre saturation point) and with defects (knots, sloping grain).
Density — denser timber is generally stronger and harder.
Good strength-to-weight ratio, low thermal conductivity (good insulator), good sound absorption, easy to work.
Shrinkage: tangential shrinkage > radial shrinkage > longitudinal shrinkage (negligible).

Common Indian timbers

Timber	Type	Features / uses
Teak	Hardwood	Highly durable, termite resistant, stable, easy to work, takes good polish — doors, windows, furniture, ship building, panelling
Sal	Hardwood	Hard, strong, heavy, durable — railway sleepers, beams, trusses, piles
Shisham (Indian rosewood)	Hardwood	Strong, durable, attractive — furniture, carving, cabinet work
Deodar	Softwood	Durable, aromatic, easy to work — doors, windows, beams in hill buildings, sleepers
Chir (pine)	Softwood	Light, less durable — packing boxes, cheap furniture, temporary work
Babul	Hardwood	Hard, tough — tool handles, cart wheels, agricultural implements
Mango	Hardwood	Cheap, not durable — packing cases, cheap furniture
Jackfruit, haldu, mahogany, oak, walnut	Hardwood	Furniture, decorative work
Bamboo	Endogenous	High tensile strength — scaffolding, low-cost structures, reinforcement in some rural works, mats and boards

Wood-based products

Product	Description / use
Veneers	Thin sheets of wood (commonly about 0.4–6 mm) obtained by rotary cutting, slicing or sawing — for plywood and decorative facing
Plywood	Odd number of veneers glued with grains of adjacent layers at right angles — strong in both directions, resists splitting and warping; types: commercial (interior), BWR/BWP (boiling water resistant/proof), marine plywood — panelling, furniture, formwork (shuttering plywood)
Blockboard	Core of wooden strips (blocks) glued edge to edge between veneers — doors, shelves, tabletops
Laminboard	Core of thin strips (laminae) — more stable than blockboard
Particle board (chipboard)	Wood chips/particles bonded with resin under heat and pressure — cheap furniture, partitions (low moisture resistance)
Fibreboards	Wood fibres bonded — hardboard (high density), insulation board (low density), medium density fibreboard (MDF) — smooth, machinable — furniture, panelling
Glued laminated timber (glulam)	Several layers of dimensioned timber glued together with grains parallel — large beams, arches, portal frames
Laminated veneer lumber (LVL)	Veneers glued with grains parallel — structural beams, headers
Cross-laminated timber (CLT)	Layers of lumber glued with alternating grain directions — structural wall and floor panels for mass timber buildings
Impreg timber	Wood impregnated with resin (e.g. phenol formaldehyde) and cured — improved dimensional stability and durability
Compreg timber	Impreg timber compressed under heat and pressure — very dense, strong — tool handles, bearings
Flush doors	Core (blockboard/particle board) faced with plywood or veneers
Bamboo mat board, bamboo composites	Eco-friendly alternatives

Measurement of timber

FormulaVolume of timber

Sawn timber: $V = L \times B \times T$

Round logs — quarter girth formula (commonly used in trade):

V = (\frac{G}{4})^{2} L

( $G$ = mean girth; $L$ = length.) It underestimates the true volume of a circular log (allowing for waste in squaring).

Worked examples

Worked ExampleExample 1 — moisture content

A timber sample weighs 5.00 kg when green and 4.20 kg when oven-dry. Find its moisture content.

Solution. $M C = \frac{5.00 - 4.20}{4.20} \times 100 = 19.0%$

Worked ExampleExample 2 — volume of a log

Find the volume of a log 5 m long with a mean girth of 2.0 m by the quarter girth formula, and compare with the true cylindrical volume.

Solution. Quarter girth: $V = (2.0/4)^{2} \times 5 = 1.25 m^{3}$ True volume: radius $= 2.0/ (2 π) = 0.318$ m → $π \times 0.31 8^{2} \times 5 = 1.59 m^{3}$ (quarter girth gives about 78.5%)

Worked ExampleExample 3 — plywood layers

Why is plywood made with an odd number of veneers with adjacent grains at right angles?

Solution. Cross-graining equalises strength and shrinkage in both directions, preventing splitting and warping; an odd number keeps the construction symmetrical about the central ply so that stresses balance and the board stays flat.

Frequently tested points

Exogenous (softwoods, hardwoods) vs endogenous (bamboo, palm).
Softwoods: conifers, distinct rings, resinous, light (deodar, pine); hardwoods: broad-leaved, strong (teak, sal, shisham).
Heartwood — dead, durable; sapwood — living, less durable; cambium forms new wood; medullary rays radial.
Seasoning reduces moisture (well-seasoned about 10–15%); fibre saturation point ~25–30%.
Kiln seasoning — quick and controlled (compartment and progressive kilns).
Quarter and radial sawing reduce warping; flat sawing is economical.
Shakes: heart, cup (ring), star, radial; knots reduce strength.
Dry rot — damp unventilated conditions; wet rot — alternate wetting and drying.
Seasoning defects: bow, cup, twist, checks, splits, honeycombing, case hardening.
Preservatives: creosote (oil type), CCA/ASCU (water-borne); pressure impregnation — Bethell (full-cell), Rueping and Lowry (empty-cell).
Large timber sections char and retain strength in fire.
Strength much higher parallel to grain; tangential shrinkage > radial > longitudinal.
Plywood: odd number of veneers, cross-grained; glulam, LVL (parallel grains), CLT (cross layers); compreg = compressed impreg.
Quarter girth formula $V = (G /4)^{2} L$ .

Common MistakeCommon mistakes

Calling all softwoods physically soft and all hardwoods hard (the terms are botanical).
Confusing dry rot (occurs in damp, unventilated places) with decay caused by dryness.
Assuming timber strength is the same in all directions.

Revision SummaryChapter summary

Timber comes mainly from exogenous trees, classified as softwoods and hardwoods; heartwood is the useful durable part.
Good timber is sound, straight-grained, defect-free, dense and well seasoned by natural or artificial methods.
Conversion methods affect appearance and stability; natural, fungal, insect, seasoning and conversion defects reduce quality.
Preservatives (creosote, CCA) applied by surface or pressure methods protect timber from decay and insects; large sections resist fire by charring.
Indian timbers such as teak, sal, shisham and deodar have characteristic uses, and engineered wood products (plywood, MDF, glulam, LVL, CLT) extend timber applications.

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