Worksite Preparation, Setting Out and Levelling
Worksite Preparation
Core concepts
Good preparation decides whether the masonry goes up straight and fast. Before the first brick is laid you must plan: site clearance, access routes, storage areas, the mortar mixing platform, water and power points, temporary fencing and security, drainage so the site does not flood, and a spoil area for stripped topsoil (stockpile it, because it will be needed for reinstatement).
Setting up the storage yard
- Cement goes on a raised, dry platform at least 150 mm off the ground, under cover, in date order, first in first out. Never stack more than about 10 bags high, and never against a damp wall.
- Bricks and blocks are stacked on firm level ground or pallets, kept square and stable, usually no higher than about 1.8 m. Never stack within about 600 mm of a trench edge.
- Sand goes on a hard standing, kept clean of clay, leaves and rubbish; aggregate is stockpiled separately so the two do not mix.
- Reinforcement, lintels and timber are kept off the ground on bearers and covered.
Work area and services
Provide a level mixing platform with a mortar board or mixing tray, a water drum with a tap, and a route for the wheelbarrow that does not cross freshly laid work. Mark out material delivery zones so lorries do not churn the access road. Protect trees, drains and existing services, and confirm where underground cables and pipes run before any excavation.
Traps in questions
Look out for cement stored directly on the ground, sand containing clay or salt, blocks stacked against a trench, and a mixing platform placed uphill from a drain with no silt control. Also remember that ordering and storing must match the programme: excess stock means waste and double handling.
Worked rule of thumb
Order with a wastage allowance: about 5 percent for cement, blocks and bricks; 5 to 10 percent for sand and aggregate. For a 1,000-block wall, order about 1,050 blocks.
Setting Out and Levelling
Core concepts
Setting out transfers the drawing to the ground; levelling fixes heights. Both must be checked before masonry starts, because an error of 20 mm at the base becomes a serious problem at roof level.
Horizontal setting out
Work from the approved plan and the site boundary or building line. Establish a baseline, then set out corners using the 3-4-5 method: a triangle with sides in the ratio 3:4:5 has a right angle between the two shorter sides. Push pegs accurately, protect them with profile boards and nails, and run string lines between them. Always verify with the diagonals: for a true rectangle, both diagonals must be equal. Allow for the wall thickness and for the mortar joint when calculating positions.
Levelling
Use an automatic or dumpy level on a firm tripod, set up roughly equidistant from backsight and foresight to cancel collimation error. The method is fixed: Height of Instrument (HI) = Reduced Level of benchmark + backsight reading then RL of new point = HI minus foresight reading. Check the level at the end of the day by taking a closing reading back to the benchmark; any discrepancy means the instrument moved.
Vertical control
Use a plumb bob or spirit level on each face, a storey rod for course heights, and a water level or laser for transferring a datum into rooms where a tripod cannot stand. Mark the finished floor level and the damp-proof course line on the setting-out profiles.
Traps in questions
Reading a staff from too far away (readings blur beyond about 30 m), parallax, a bent staff, string line sag over long spans, and forgetting to check the diagonals. Also common: setting out to grid lines without checking them against the architect's dimensions.
Worked example
Benchmark RL = 12.500 m; backsight = 1.320 m, so HI = 13.820 m. A foresight of 2.045 m gives RL = 13.820 - 2.045 = 11.775 m.