Building Technology and Construction
Substructure and superstructure
This domain tests construction sequence and workmanship detail. Substructure: setting out from the site datum, excavation to the required depth, foundation type (strip, pad, raft or pile) matched to the soil, hardcore compacted in layers, damp-proof membrane, oversite concrete and a damp-proof course at least 150 mm above external ground level. Superstructure: masonry in stretcher or English bond, columns and beams cast to line and level, lintels over openings with adequate bearing, wall ties, movement joints, then roof structure and covering with ventilation and insulation.
Control points
Concrete: correct grade, controlled water-cement ratio, thorough compaction and curing for at least seven days. Masonry: blocks wetted as required, mortar 1:4 to 1:6, 10 mm joints, plumb and level checked course by course, controlled daily lift. Moisture: DPC continuous and not bridged by mortar droppings; damp-proof course under sills. Tolerances: about 10 mm on setting out and on plumb over a storey height.
Worked example
A 120 m² slab at 150 mm thick needs 18 m³ of concrete. A nominal 1:2:4 mix yields roughly 6.5 bags of 50 kg cement per cubic metre, so 18 x 6.5 = 117 bags, plus 5% wastage, about 123 bags, with sand and coarse aggregate ordered in the same volume ratio.
Traps
Treating 1:2:4 as a design mix suitable for every element; forgetting compaction and wastage in ordering; laying the DPC below finished ground level so it is bridged; casting a slab with no curing regime in harmattan heat.