Blocklaying and Masonry Construction
Blocklaying questions test bond, gauge, plumb, level, joint thickness and how you organise the work so corners lead and the line follows. Answers must use the trade’s own words: quoin, rack back, toothing, perpend, bed joint, line, gauge rod.
Bonds and gauge
- Stretcher (half-block) bond: the everyday bond; each block overlaps the one below by half a block.
- English bond: alternating header and stretcher courses; strongest.
- Flemish bond: header and stretcher alternate within the same course; decorative.
- Stack bond: no overlap, weak - only with reinforcement or ties. With 450 × 225 × 150 mm blocks and a 10 mm joint the module is 460 × 235 mm, giving about 9.25 blocks per m² of wall face (allow 10 per m² or add 5% for waste). Course height is 235 mm.
Laying sequence
- Lay the damp-proof course on a levelled footing.
- Build the quoins (corners) first, checking plumb and level on every course, and rack them back one half-block per course.
- Stretch a line between corners and lay to it, face to the line.
- Full bed and full perpend joints, 10 mm thick - no dry joints and no shiners (blocks laid on their sides to show a wide face).
- Check level and plumb each course; the gauge rod controls height and openings.
- Tooth the day joint; do not raise more than about 1.2–1.5 m of wall in a day.
- Rake out and point, or finish the joint as specified.
- Protect and cure the wall against fast drying and rain.
Mortar
1:4 or 1:5 cement:sand for load-bearing blockwork; 1:6 for internal non-load-bearing work. Mix on a board, use within about two hours (one hour in hot weather), and never revive a stiffened mix with water. Do not soak sandcrete blocks; damp very dry ones only.
Worked example
A wall 6.0 m long × 2.7 m high has a 1.2 × 2.1 m opening. Gross area = 16.20 m²; opening = 2.52 m²; net = 13.68 m². At 9.25 blocks/m²: 13.68 × 9.25 = 126.5, say 127 blocks. Add 5% for cutting and breakage: 127 × 1.05 = 133. Order 133–140 blocks.
Traps that cost marks
Joints thicker than 12 mm, which weakens the wall; over-strong 1:3 mortar causing shrinkage cracks; laying blocks hollow-face up when the specification says otherwise; leaving perpends unfilled; building too far ahead without toothing; checking plumb only at the end of the day.