Laying and Bonding of Masonry Units
This domain tests laying concrete hollow blocks or other masonry units to line, level, and plumb, with correct bond, joint thickness, and opening preparation. The exam looks for full joints, staggered units, consistent coursing, and checking as the wall rises.
Core rules
- Set out and build the corners first, then run a string line between them.
- Lay units on a full mortar bed and fill head joints fully; nominal joint thickness is usually 10 mm unless specified otherwise.
- Stagger vertical joints in running bond by half a unit; avoid continuous vertical joints unless the design calls for stack bond.
- Check level, plumb, and line every course, not only at the top.
- Cut units neatly at openings and corners; do not use broken units in exposed faces.
- Leave openings, chases, and control joints as detailed, and do not overload a green wall.
Worked example
A 200 mm high concrete hollow block with a 10 mm joint gives a course height of 210 mm. Ten courses therefore reach 2.10 m. If a window sill is scheduled at 2.10 m, the sill course can be set after ten courses, provided the first course is level and joint thickness is controlled. The reasoning is that coursing is cumulative: a joint that is consistently 15 mm instead of 10 mm adds 50 mm over ten courses and throws out the sill height.
Traps
- Thick bed joints used to correct an uneven first course.
- Head joints left hollow or partly filled.
- Checking plumb only at the end of the wall.
- Using broken blocks in the face work.
Key points
- Build corners first and run a string line.
- Fill bed and head joints fully.
- Stagger joints by half a unit in running bond.
- Check level and plumb every course.
- Control joint thickness to keep coursing accurate.