Punjab PSEB Matric NSQF Construction cheat sheet

Standard brick size in India is 190 × 90 × 90 mm (modular) with a 10 mm mortar joint giving 200 × 100 × 100 mm nominal; traditional brick is 230 × 110 × 70 mm.

Mortar mixes by volume: 1:3 (cement:sand) for load-bearing masonry and plaster of high strength, 1:4 for general brickwork, 1:6 for internal plaster and non-structural work.

Concrete nominal mixes per IS 456: M5 = 1:5:10, M7.5 = 1:4:8, M10 = 1:3:6, M15 = 1:2:4, M20 = 1:1.5:3, M25 = 1:1:2 (cement:sand:coarse aggregate).

Cement setting: initial setting time must not be less than 30 minutes and final setting time not more than 600 minutes; cement older than 3 months should be retested before structural use.

Plaster thickness: 12 mm for brick masonry internal walls, 15–20 mm for external walls and rough surfaces; mortar 1:4 to 1:6 is typical for internal plaster.

Slump test measures workability of fresh concrete; typical slump for normal RCC work is 25–75 mm, and for heavily reinforced sections 75–125 mm.

Bearing capacity of soil is expressed in kN/m²; safe bearing capacity (SBC) is the ultimate bearing capacity divided by a factor of safety, commonly 2.5 to 3.

Levelling instruments: a dumpy level uses a fixed telescope with a bubble tube; an auto level uses a compensator to keep the line of sight horizontal automatically.

Setting out a right angle: 3-4-5 method - measure 3 m along one line, 4 m along the other, and adjust until the diagonal reads 5 m.

Plumb of a masonry wall is checked with a plumb bob or spirit level; a 600 mm spirit level detects vertical deviation along its length, and a mason's square checks corners.

Mortar estimation example: 1 m³ of 1:6 mortar needs about 0.30 m³ cement (about 9 bags at 50 kg) and 1.8 m³ sand, allowing 30% bulking of sand and 33% dry-volume factor.

Brickwork quantity: a 230 mm thick wall of 1 m² area needs about 500 bricks per m³; for 1 m³ of brickwork allow roughly 500 bricks plus 0.30 m³ mortar.

Curing: concrete must be kept moist for at least 7 days for ordinary Portland cement and 10 days in hot, dry weather; ponding, wet gunny bags, or sprinkling are accepted methods.

Plastering sequence: clean and wet the surface, apply a 1:3 to 1:4 cement mortar backing coat, roughen it, then apply the finishing coat; curing follows for at least 7 days.

Safety on site: a helmet, safety shoes, and high-visibility vest are mandatory; scaffold working platforms must be at least 600 mm wide with guardrails at 900 mm and 1800 mm height.

Level booking: reduce level (RL) of a point = height of instrument (HI) minus staff reading; HI = known RL + backsight reading.