WBCHSE HS Vocational Construction cheat sheet

Standard brick (modular): 190 × 90 × 90 mm; conventional Indian brick: 230 × 110 × 70 mm including mortar joint; weight about 3.0–3.5 kg.

Good brick tests: water absorption ≤ 20% by weight (1st class ≤ 15% after 24 h immersion), compressive strength ≥ 3.5 N/mm² (1st class ≥ 10 N/mm²), free from efflorescence and salt deposits.

OPC grades in India: 33, 43, 53 (28-day compressive strength in N/mm²); initial setting time ≥ 30 min, final setting time ≤ 600 min.

Aggregate sizes: fine aggregate (sand) passes 4.75 mm IS sieve; coarse aggregate 20 mm for RCC, 40 mm for mass concrete; sand should have silt ≤ 3% by volume for good concrete.

Timber moisture content for carpentry: 8–12% for interior work; shrinkage is greatest along the tangential direction, least along the longitudinal.

Thermal conductivity (k) order: copper > steel > concrete > brick > timber > thermocol; lower k means better insulation.

Sound insulation improves with mass (heavy walls) and with air gaps or resilient layers; porous materials absorb sound but do not block it.

Paint coverage rule: 1 litre covers about 10 m² per coat on smooth plaster; primer coat needed before putty and finish coats.

Masonry tools: trowel (brick/gauging), plumb bob (verticality), spirit level (levelness), mason's square (right angles), line and pins (course alignment).

Carpentry tools: try square (90° checking), marking gauge (parallel lines), rip saw (along grain), cross-cut saw (across grain), chisel (mortise work).

Concrete equipment: concrete mixer (drum or pan), vibrator (needle for RCC, surface for slabs), batching plant, transit mixer, concrete pump.

Earthmoving equipment: excavator (digging), backhoe loader (trenching), bulldozer (pushing/levelling), grader (finishing subgrade), roller (compaction).

Lifting equipment: chain pulley block, crane, hoist; safe working load (SWL) must be marked and never exceeded.

Personal protective equipment (PPE): helmet, safety shoes, goggles, gloves, ear plugs, dust mask, full-body harness for work above 1.8 m.

Scaffolding rule: working platform width ≥ 1 m, guardrail 900–1000 mm high, toe board 150 mm; never use damaged planks or bamboo without lashing.

Fire safety: keep extinguishers near hot work, no open flame near solvent paints; electrical tools must be earthed and use ELCB/RCCB.

Scale meaning: 1:100 means 1 unit on paper = 100 units on ground; 1:50 gives twice the drawing size of 1:100 for the same object.

Line types: continuous thick (visible outline), continuous thin (dimension, hatching), dashed (hidden), chain/dash-dot (centre line), wavy (break line).

Plan is a horizontal section cut at about 1.2 m above floor level; section shows vertical cut; elevation shows outside face.

Dimension convention: dimensions in mm on structural drawings; arrowheads or oblique strokes at ends; do not repeat dimensions on both plan and section.

North direction and scale must appear on every drawing sheet; title block carries project name, drawing number, scale, date, and initials.

Symbols: door swing as quarter circle, window as double line in wall, sanitary fixtures as standard plan symbols, electrical points as circles with letters.

Staircase drawing rule: riser × 2 + tread ≈ 600–640 mm (comfort formula); minimum riser 150 mm, maximum 190 mm for residential.

Site plan scale typically 1:500 to 1:1000; detail drawing 1:20 or 1:10; use appropriate scale so the drawing is readable.

Brick bonds: stretcher (all stretchers on face), header (all headers), English (alternating header and stretcher courses), Flemish (header and stretcher alternating in same course).

English bond is strongest for walls; Flemish bond gives better appearance; rat-trap bond saves about 25% bricks and improves thermal insulation.

Mortar mixes: 1:3 (1 cement : 3 sand) for load-bearing masonry, 1:4 for general work, 1:6 for non-load-bearing partitions.

Standard mortar joint thickness: 10 mm; brickwork should be soaked before laying and cured for at least 7 days.

Quoins are corner stones/bricks; a queen closer is a brick cut in half along its length; a king closer is cut diagonally.

Stone masonry: rubble (random or coursed) and ashlar (dressed, square, fine joints 3–6 mm); ashlar is stronger and more expensive.

Plumb and level checks: each course must be checked with plumb bob and spirit level; maximum permissible deviation 5 mm per storey.

Toothing and raking back: walls left for future extension must be toothed at 1/4 brick depth; do not leave straight vertical joints.

Nominal concrete mixes: M15 (1:2:4), M20 (1:1.5:3), M25 (1:1:2) by volume; M20 is the minimum grade for RCC in normal exposure.

Water-cement ratio: 0.5 for M20 typical; lower w/c gives higher strength and durability; excess water reduces strength by about 15–20% per 0.1 increase.

Workability tests: slump (typical 25–75 mm for RCC), compaction factor, Vee-Bee; slump is not a measure of strength.

Curing: minimum 7 days for OPC concrete, 10–14 days for blended cement or hot weather; keep surface moist.

Formwork removal: sides of beams/columns after 24–48 h; soffit of slab after 7 days (props retained); beams after 14 days; full props after 21 days.

Reinforcement: main bars in tension zone, distribution/stirrups in the perpendicular direction; cover 40 mm for columns, 25–30 mm for slabs, 50 mm for footings.

Steel grades: Fe415 and Fe500 (yield strength in N/mm²); lap length typically 50d in tension and 45d in compression for Fe415.

Compaction: needle vibrator for beams/columns, surface vibrator for slabs; over-vibration causes segregation, under-vibration causes honeycombing.

Joint types: butt, lap, mortise-and-tenon, dovetail, dowel, tongue-and-groove, halving; mortise-and-tenon is strong for frames.

Seasoning of timber reduces moisture and prevents warping; kiln seasoning is faster than air seasoning.

Wood defects: knots (cut branch base), shakes (splits), warp (distortion), rot (fungal decay), sapwood is weaker than heartwood.

Common carpentry joints in doors: mortise-and-tenon for stiles and rails; dowel or loose tenon for panel doors.

Standard door sizes: 900 × 2100 mm (main), 750 × 2100 mm (bathroom); door frame section 100 × 63 mm typical.

Preservative treatment: creosote for exterior timber, copper-chrome-arsenate (CCA) for interior and exterior, paint or varnish for surface protection.

Plywood is made of odd number of veneers glued with grain at right angles; blockboard has a core of softwood strips.

Tools sharpening angle: plane iron 25°; chisel 25°; saw teeth set alternately to prevent binding.

Plumbing: GI (galvanised iron), CI (cast iron), PVC, CPVC, and PPR pipes; CPVC for hot water, PVC for soil waste; GI for cold water supply.

Water supply pressure: minimum residual pressure at fixture 0.5–1.0 m head; overhead tank bottom at least 2 m above the highest fixture.

Sanitary fittings: water closet (WC), wash basin, sink, floor trap, gully trap, inspection chamber, manhole; traps prevent sewer gas entry.

Slope of drain pipes: 1:40 to 1:60 for 100 mm soil pipe; 1:80 to 1:100 for 150 mm; minimum self-cleansing velocity 0.6 m/s.

Electrical: single-phase 230 V, three-phase 415 V, 50 Hz in India; earth wire green, live red/brown, neutral black/blue.

Circuit protection: MCB (miniature circuit breaker), ELCB/RCCB (earth leakage), fuse; MCB rating must match cable current capacity.

Lighting points: one light point per 10–15 m² of floor area; switch height 1.2 m, socket height 0.3 m or 1.2 m as per design.

Earthing: pipe earthing or plate earthing; earth resistance should be ≤ 1 ohm for sensitive equipment, ≤ 5 ohm general.

Types of estimate: preliminary (approximate), detailed (item-wise), revised, supplementary; detailed estimate uses measurement sheets and abstract of cost.

Units: earthwork in m³, brickwork in m³, plaster in m², painting in m², reinforcement in kg or quintal, pipes in running metre.

Brickwork quantity: length × height × thickness; deduct openings > 0.1 m²; no deduction for openings ≤ 0.1 m².

Plaster quantity: area = length × height; deduct openings > 0.5 m²; add 10% for grooves and edges if specified.

Concrete quantity: volume = L × B × D; add 2.5% for wastage; steel quantity = (mass per metre) × length; 1 m of 12 mm bar ≈ 0.888 kg.

Rate analysis: cost of materials + labour + plant + overheads + contractor's profit (typically 10–15%) + GST as applicable.

Centre line method: total centre line length × breadth × depth; for walls meeting at corners, subtract half breadth at each junction.

Contingency and work-charged establishment: 3–5% contingency, 1–2% work-charged establishment added to estimated cost.

Project phases: feasibility, planning/design, procurement, construction, commissioning, handover.

Bar chart (Gantt) shows activities against time; CPM shows critical path (longest path, zero float); PERT uses three time estimates (optimistic, most likely, pessimistic).

Float (slack) = LS − ES = LF − EF; critical activities have zero float; delaying them delays the project.

Cost control: S-curve of cumulative cost vs time; earned value = BCWP; cost variance = BCWP − ACWP; schedule variance = BCWP − BCWS.

Quality control: checklists, slump test, cube test (28-day), sieve analysis, level and plumb checks; non-conformance reports.

Safety management: induction training, toolbox talks, PPE enforcement, incident reporting, first aid, emergency exits.

Labour productivity: mason lays about 1.0–1.5 m³ of brickwork per day; a carpenter fixes about 3–5 m² of shuttering per day.

Contract types: lump sum, item rate, percentage rate, cost plus; item rate is common for public works in India.

Entrepreneur functions: idea generation, feasibility study, business plan, resource mobilisation, risk bearing, innovation.

Small business registration in India: Udyam registration (MSME), GST registration if turnover exceeds threshold (₹40 lakh for goods, ₹20 lakh for services).

Costing terms: fixed cost (rent, salaries), variable cost (materials, wages), break-even point = fixed cost / (selling price − variable cost per unit).

Marketing mix 4Ps: product, price, place, promotion; for construction services, credibility and past projects drive demand.

Communication skills: active listening, clear technical writing, drawing reading, site reporting, email etiquette.

Employability: resume, interview preparation, teamwork, time management, problem solving, digital literacy (MS Office, AutoCAD basics).

Financial literacy: maintain cash book, invoice, GST invoice format, quotation, and record of measurements for billing.

Government schemes: PMEGP, MUDRA loans, Stand-Up India, Skill India; subsidies and credit support for micro-enterprises.

Practical tasks: brick masonry in English bond, plastering, concrete cube casting, carpentry joint, plumbing layout, electrical wiring board.

Measurement and testing: slump test, cube compressive test, sieve analysis, water absorption of brick, level and plumb checks.

Project report structure: title, aim, materials, tools, procedure, observations, results, conclusion, references.

Viva preparation: know tool names and uses, material properties, standard sizes, mix ratios, and safety rules.

Site visit records: date, location, work observed, labour and equipment used, safety measures, photographs (if permitted), and notes.

Drawing sheet submission: plan, elevation, section to scale, with title block, dimensions, north arrow, and scale.

Estimation exercise: measure a small room, compute brickwork, plaster, concrete, and prepare an abstract of cost.

Common viva questions: difference between nominal and design mix, purpose of curing, why cover is provided to reinforcement, types of bonds.