Walls, Masonry and Concrete Construction
What the domain tests
Walls, Masonry and Concrete Construction tests brick and block bonds, mortar, cavity walls, lintels, concrete mixes, reinforcement, formwork, placing, compaction and curing.
Core rules
- Standard brick size is 222 x 106 x 73 mm with 10 mm joints. Common bonds include stretcher, header, English and Flemish.
- Mortar is specified by mix, commonly 1:3 to 1:6 cement to sand. Use the specified mix and do not add water to improve workability.
- Keep walls plumb, level and straight; use a gauge line and quoin blocks; tooth or bond corners correctly.
- Cavity walls need wall ties, a clean cavity, DPC and weep holes.
- Concrete is specified by grade, such as 25 MPa. Control water-cement ratio, compact properly and cure for the specified period, often 7 days.
- Reinforcement needs correct cover, laps and chairs; do not walk on mesh.
Worked example
A slab is 5 m x 4 m x 0.1 m = 2.0 m³. For a 1:2:4 mix, use a dry-volume factor of 1.54. Total parts = 7. Cement volume = 2.0 x 1.54/7 = 0.44 m³. At 1440 kg/m³, cement = 634 kg, about 13 bags of 50 kg. Sand is 0.88 m³ and stone 1.76 m³. Reasoning: convert wet volume to dry, divide by parts, then convert cement volume to mass.
Traps
- Adding water to stiffen or soften concrete without approval.
- Curing for only one day.
- Poor bonding at corners.
- Insufficient cover to reinforcement.
- Using mortar that has begun to set.