WBBSE Madhyamik Vocational Construction cheat sheet

Brick earth (good brick): free from lime nodules, uniform colour, ringing sound when struck, water absorption ≤ 20% by mass after 24 h soaking, compressive strength ≥ 3.5 N/mm² for common burnt clay bricks (Class designation per IS 1077).

Cement: OPC 33/43/53 grades denote 28-day compressive strength in N/mm² of mortar cubes; initial setting time ≥ 30 min, final setting time ≤ 600 min; soundness by Le Chatelier or autoclave test.

Mortar mix 1:6 (cement:sand) for brickwork in general walls, 1:4 for load-bearing/rich work; sand should be clean, well graded, silt content ≤ 5% for plastering and ≤ 8% for concrete.

Concrete nominal mixes: M15 (1:2:4), M20 (1:1.5:3), M25 (1:1:2); water-cement ratio controls strength and workability - lower w/c gives higher strength but lower slump.

Aggregate: coarse aggregate size 20 mm for normal RCC, 10–12 mm for thin sections; flakiness and elongation indices should be low; bulking of sand up to 20–30% with moisture affects volume batching.

Timber: seasoning reduces moisture and shrinkage; defects include knots, shakes, warping and decay; teak and sal are strong, durable hardwoods, while softwoods need treatment.

Steel: mild steel (Fe 250) has yield strength 250 N/mm²; HYSD/TMT bars Fe 415 and Fe 500 give higher yield strength; steel is ductile and bonds well with concrete, and must be free from rust and oil before use.

Lime: fat lime (pure, slakes readily, used for whitewashing) versus hydraulic lime (sets under water, used in mortar); lime mortar gains strength slowly by carbonation.

Substructure (foundation, plinth) transmits loads to soil; superstructure includes walls, columns, beams, slabs, roof, floors, doors, windows and stairs.

Foundation types: shallow (isolated footing, combined footing, raft) for firm soil at shallow depth; deep (pile, well/caisson) for weak or deep-bearing soil. Width of footing increases with load and decreases with soil bearing capacity.

Brick bonds: stretcher (½ brick thick, all stretchers), header (all headers), English bond (alternate header and stretcher courses, strongest), Flemish bond (headers and stretchers alternate in each course).

Walls: 230 mm (one brick) and 115 mm (half brick) nominal thickness; mortar joints 10 mm; toothing and quoin are used when joining old and new walls.

RCC slab and beam: formwork removed after 7 days for slabs/beams up to 4.5 m span and 14 days for longer spans (per IS 456 guidance for OPC); props and centering must be stable.

Doors and windows: lintel/sunshade above openings; sill level and chajja details; standard door sizes commonly 900 × 2100 mm, window 1200 × 1200 mm.

Stairs: riser 150–190 mm, tread 250–300 mm, width ≥ 900 mm; headroom ≥ 2100 mm; number of risers per flight limited for comfort.

Damp proof course (DPC) at plinth level, usually 40–50 mm cement concrete 1:2:4 with waterproofing compound, prevents rising dampness; damp-proofing also via plinth protection and cavity walls.

Masonry tools: trowel (gauging and laying mortar), plumb bob and spirit level (checking verticality and level), mason's square, line and pins, bolster and chisel for cutting bricks.

Carpentry tools: try square (90° checking), marking gauge, rip saw and cross-cut saw, plane, chisel, mallet, claw hammer; sharpening angle for chisels typically 25–30°.

Measuring and layout: measuring tape (steel tape for accuracy), folding rule, chalk line, pegs and string for setting out; tape must be held taut and read at eye level to avoid parallax.

Concrete equipment: concrete mixer (drum type), vibrator (needle for internal compaction), wheelbarrow, tamping rod; vibrator should be inserted vertically and withdrawn slowly to avoid segregation.

Excavation and lifting: spade, pickaxe, crowbar, shovel; hoist or crane for lifting; never exceed safe working load (SWL) marked on slings and chains.

Power tool safety: check insulation and earthing, use residual current device (RCD), keep guards in place, wear goggles and dust mask when cutting or grinding, and disconnect before changing blades.

Hand tool care: store tools clean and dry, oil metal parts to prevent rust, replace split handles, and never use a chisel as a lever or a wrench as a hammer.

Ladder and scaffold handling: ladder set at about 75° (1 in 4 rule), extend 1 m above landing; scaffold must have guardrails, toe boards and base plates on firm ground.

Scale = drawing distance / ground distance; representative fraction (RF) e.g. 1:1000 means 1 unit on paper = 1000 units on ground.

Chain survey: 20 m or 30 m chain, arrows, ranging rods, pegs; survey lines include base line, tie line and check line; check line verifies the framework.

Ranging: direct ranging by eye between two points when intervisible; indirect ranging when obstacles intervene; offsets are perpendicular (right) or oblique distances from survey line to object.

Pythagorean rule 3-4-5 sets a right angle; used to erect perpendiculars and set out corners accurately on site.

Leveling: dumpy or auto level with tripod and staff; reduced level (RL) = height of instrument (HI) − staff reading; HI = RL of benchmark + backsight.

Rise and fall method: rise = previous staff reading − next staff reading (positive rise, negative fall); arithmetic check: Σ backsight − Σ foresight = Σ rise − Σ fall = last RL − first RL.

Height of collimation method: HI = RL + backsight; RL of point = HI − intermediate/foresight; arithmetic check: Σ BS − Σ FS = last RL − first RL.

Contouring: contour lines join points of equal elevation; closer contours indicate steeper ground; contours never cross except at an overhanging cliff, and form V shapes pointing upstream at valleys.

Setting out a building: establish two reference lines (base lines) at right angles, mark corners with pegs, and verify diagonals are equal for a rectangular layout.

3-4-5 method: if sides are in ratio 3:4:5 (e.g. 3 m, 4 m, 5 m), the angle between the 3 and 4 sides is exactly 90°, used to set out perpendicular corners.

Diagonal check: for a rectangle of sides a and b, diagonal d = √(a² + b²); equal diagonals confirm squareness of the setting out.

Centre line method and long wall–short wall method are the two standard take-off methods for walls; long wall length measured out-to-out, short wall in-to-in.

Measurements in running metre for linear items (skirting, cornice), square metre for areas (plaster, painting, flooring), cubic metre for volumes (earthwork, concrete, brickwork).

Deductions: for openings in brickwork deduct area of opening × wall thickness; for plaster deduct openings exceeding 0.3 m²; for painting, deduct openings and add jambs.

Levels and datums: fix a site benchmark, transfer levels with a level or water level; plinth level, sill level, lintel level and roof level are recorded on a level sheet.

Tolerances: verticality within about 5 mm per storey, and line/level checked with spirit level and plumb; measurements recorded to nearest 5 mm or 10 mm as per practice.

Drawing sheet layout: title block (project, scale, date, drawing number), plan, elevation, section, and notes/specifications; north arrow indicates orientation.

Plan is a top view cut horizontally; elevation shows external face; section shows internal cut with hatch patterns for materials (brick hatching, concrete dots, timber grain).

Line types: continuous thick for visible outlines, dashed for hidden edges, chain/dash-dot for centre lines and grid lines, and thin lines for dimension and extension lines.

Dimensioning: dimension line with arrowheads, extension lines, and figures above the line; all dimensions in millimetres unless noted; overall and sub-dimensions must agree.

Scales: 1:100 for plans, 1:50 for detailed plans, 1:20 or 1:10 for sections and details; graphic scale remains valid if the drawing is photocopied at a different size.

Symbols: door swing arc, window double lines, staircase arrow showing direction of ascent, section cut line with arrows showing viewing direction, and abbreviations like FFL (finished floor level), GL (ground level).

Reading a blueprint: identify grid lines and column centres, check wall thickness, opening sizes, beam/slab depths, and cross-check plan with section for consistency.

Working drawings include foundation plan, floor plan, structural layout, electrical and plumbing layouts; bar bending schedule (BBS) gives bar mark, diameter, shape, length and number.

Personal protective equipment (PPE): helmet, safety shoes, goggles, gloves, ear plugs, dust mask and high-visibility vest; PPE is the last line of defence after eliminating hazards.

Head protection: helmets replaced after impact or about 3–5 years of use; chin strap fastened when working at height.

Falls are a leading site hazard: use guardrails, safety nets, harness anchored to a lifeline, and cover or barricade floor openings.

Electrical safety: use 110 V or RCD-protected supply on wet sites, keep cables off the ground, lock out/tag out before maintenance, and never touch live parts.

Excavation safety: shore or slope trenches deeper than 1.5 m, keep spoil at least 1 m from the edge, provide ladders for access, and check for underground services before digging.

Hazardous substances: cement dust is alkaline and can cause dermatitis and eye injury; wet cement burns skin, so wear gloves and wash exposed skin; silica dust from cutting concrete can cause silicosis.

Housekeeping and environment: segregate waste, control dust by sprinkling water, prevent oil spillage, and follow noise limits and working-hour rules near residential areas.

First aid and emergency: know the location of first-aid box, fire extinguisher and emergency numbers; report all incidents; a near miss should be recorded and investigated.

Estimate types: approximate (plinth area, cubical content, unit rate) versus detailed estimate based on measured quantities and item rates; detailed estimate = quantity × rate plus overheads and contingency.

Plinth area estimate: cost = plinth area × plinth area rate; cubical content method: cost = volume (L × B × H) × unit cubic rate.

Earthwork in excavation = length × breadth × depth; for foundation trenches, measure centre-line or long wall–short wall lengths and multiply by trench width and depth.

Brickwork volume = length × height × thickness − volume of openings; use nominal wall thickness (230 mm for one brick) and deduct DPC, lintels and openings as per rules.

Plaster quantity = surface area × thickness; mortar volume converted to dry volume by multiplying by 1.30–1.35 to account for voids in sand.

Concrete volume = L × B × D; dry volume of concrete = wet volume × 1.52–1.54; cement bags = cement volume × 1440 kg/m³ ÷ 50 kg per bag.

Steel reinforcement take-off from bar bending schedule: weight (kg) = (d²/162) × length in m, where d is bar diameter in mm; add lap and hook lengths as specified.

Rate analysis: rate per unit = (cost of materials + labour + plant + overheads + profit) ÷ quantity; wastage allowances commonly 3–5% for cement, sand and bricks.

Brickwork practice: lay the first course on a level mortar bed, check line and level, keep vertical joints 10 mm and staggered; fill joints fully and strike them neatly.

Plastering practice: prepare surface, apply 12 mm thick mortar in one or two coats, use screeds and floats, check with straight edge, and cure for at least 7 days.

Concreting practice: measure materials by volume or weight, mix to uniform colour, place in layers, compact with a tamping rod or vibrator, and cure for 7–14 days.

Carpentry practice: measure and mark with try square and marking gauge, saw on the waste side of the line, chisel with the bevel side down, and check squareness before assembly.

Plumbing and electrical project work: cut threads squarely, apply jointing compound, pressure-test for leaks; for wiring use correct colour code and terminate firmly in junction boxes.

Measurement and record keeping: maintain a work diary of dates, labour, materials used and progress; take site measurements jointly and record in a measurement book (MB).

Quality checks: check brick alignment with plumb and line, concrete slump, plaster thickness, and level of finished surfaces; reject work that fails tolerance before proceeding.

Project work sequence: study drawing, prepare material list and estimate, plan sequence of operations, execute with safety checks, then inspect, measure and hand over.