Masonry and Concreting Works
This domain tests brick and block laying to line, level and plumb, and the batching, placing, compacting and curing of concrete.
Brick masonry
Soak burnt clay bricks in clean water before laying so they do not draw water from the mortar. Use a 10 mm joint and 1:4 to 1:6 cement-sand mortar for load-bearing work, and lay to a tightened line checked with spirit level and plumb rule. Bonds: stretcher for half-brick walls, header for one-brick, English with alternate header and stretcher courses, Flemish with alternate headers in each course, and rat-trap for economy. Rake joints for a plaster key and do not raise a wall more than about 1 m a day.
Concrete
Nominal mixes: M15 is 1:2:4 and M20 is 1:1.5:3 by volume; design mixes are by weight. The water-cement ratio controls strength and durability, about 0.5 for normal work. Extra water gives workability but each 0.1 rise in w/c can cut strength by roughly 15 to 20%. The slump test measures workability. Compact with a vibrator to avoid honeycombing. Cure for at least 7 days, and 14 days in hot weather or for rich mixes, keeping the surface moist.
Worked example
50 kg of cement at w/c 0.50 needs 25 litres of water. If the sand carries 4% moisture and you use 100 kg of it, that sand already brings 4 litres, so add only 21 litres at the mixer. Ignoring aggregate moisture is how slabs end up weak and cracked.
Traps
Adding water on site to make the mix easier, curing for a single day, joints thicker than 10 mm, laying dry bricks, and striking formwork too early.