Masonry: Trade Theory and Practical Fundamentals
Materials and Units
Masonry work depends on understanding the materials you handle daily. Bricks are classified by quality and use: first-class bricks are well burnt, uniform in colour, sharp-edged, and give a clear ringing sound when struck together; second-class bricks are slightly irregular and used where less finish is needed; third-class (picked) bricks are over-burnt or under-burnt and reserved for temporary or foundation work. Mortar binds units into a monolithic mass. Cement mortar (cement:sand, commonly 1:3 to 1:6) is strong and quick-setting; lime mortar is more workable and flexible; gauged mortar adds cement to lime mortar for economy and workability. Mortar should be used within about 30 minutes of mixing to avoid loss of strength.
Bonds and Joints
A bond is the pattern of arranging units so that vertical joints do not align from course to course. Key bonds: stretcher (all stretchers, half-brick thick), header (all headers, one-brick thick), English (alternate courses of headers and stretchers), Flemish (headers and stretchers alternate within each course), and rat-trap (used for economy and insulation). Joints should be about 10 mm thick and uniform; thicker joints reduce strength. The mortar joint is the weakest plane, so good bond prevents continuous vertical joints.
Setting Out and Levelling
Practical questions often test setting out: establish a datum, use a builder's square (3-4-5 method) to set a right angle, and check courses with a spirit level and plumb rule. Quoins (corner stones) are raised first and act as guides. Line and pins control course alignment.
Traps to Watch
Questions may confuse stretcher with header dimensions, or ask which bond is used for a one-brick wall (English or Flemish). Another common trap: assuming thicker mortar is stronger - it is weaker. Also, do not confuse curing (keeping masonry moist after laying) with setting.
Worked Rule of Thumb
For a 1:6 cement mortar, mix 1 part cement to 6 parts sand by volume; add only enough water for a workable, buttery consistency. As a rule, one brick plus one 10 mm joint gives a nominal module of 200 × 100 × 75 mm; use this to estimate brick quantity: about 500 bricks per cubic metre of brickwork.