The foundations for walls are laid in a concrete mix of 1 : 2 ½ : 4 which is placed in layers about 75 mm thick and tamped with a piece of wood about 50 mm square. There is no need to make a neat finish, but the concrete must be levelled off to the tops of the pegs which have been driven into the bottom of the trench. When this has been done the pegs can be pulled out and the holes made good.
Walls built with broken slabs, in order to give a rough stone-like appearance, can be difficult to plumb and much depends on the ability of the operator. Small pieces of wood can be built into the joints so that they project clear of the rough surface of the blocks, each piece projecting by the same amount so that a plumb level can be placed against them to assist the eye in keeping the wall vertical. These building blocks are cast like other blocks, but twice the required width so that they can be broken in two while they are still ‘green’. Proprietary blocks are made in shaped moulds and often have a walling pattern cast on the face so that when they are laid it is difficult to see that they are really rectangular blocks, all of the same size. Ordinary plain building blocks are laid in the same way as bricks, but it is advisable when using blocks under 75 mm 98 thick, not to take the wall higher than about 1220 mm without leaving the mortar to set for a day otherwise the wall may buckle.
Where large decorative blocks are used, the mortar mix should be a little stiffer than that generally used for building with bricks, because these blocks are heavier than bricks and will squeeze more mortar out of the joints. Care must be taken to prevent mortar staining the face of decorative work.
The main tools needed for concreting are shovels for mixing and laying, trowels for patching, steel and wooden floats for finishing surfaces. Bending equipment may be needed where reinforcing is involved, and of course, mechanical mixers and vibrators are needed where a lot of concreting is to be undertaken. A strong wheelbarrow will be needed to transport the concrete from the mixing point to the site where it is to be placed. All the tools must be washed in clean water as soon as possible after use to keep them in good condition and ready for future use.