Moulded bricks – These bricks start with raw clay, preferably in a mix with 25–30% sand to reduce shrinkage. The clay is first ground and mixed with water to the desired consistency. The clay is then pressed into steel moulds with a hydraulic press. The shaped clay is then fired at to achieve strength. Dry-pressed bricks – The dry-press method is similar to the soft-mud moulded method, but starts with a much thicker clay mix, so it forms more accurate, sharper-edged bricks. The greater force in pressing and the longer firing time make this method more expensive. Extruded bricks – For extruded bricks the clay is mixed with 10–15% water (stiff extrusion) or 20–25% water (soft extrusion) in a pugmill. This mixture is forced through a die to create a long cable of material of the desired width and depth. This mass is then cut into bricks of the desired length by a wall of wires. Most structural bricks are made by this method as it produces hard, dense bricks, and suitable dies can produce perforations as well. The introduction of such holes reduces the volume of clay needed, and hence the cost. Hollow bricks are lighter and easier to handle, and have different thermal properties from solid bricks. The cut bricks are hardened by drying for 20 to 40 hours at before being fired. The heat for drying is often waste heat from the kiln.
Moulded bricks – These bricks start with raw clay preferably in a mix with 25–30% sand to reduce shrinkage The clay is first ground and mixed with water to the desired consistency The clay is then pressed into steel moulds with a hydraulic press The shaped clay is then fired at to achieve strength Dry-pressed bricks – The dry-press method is similar to the soft-mud moulded method but starts with a much thicker clay mix so it forms more accurate sharper-edged bricks The greater force in pressing and the longer firing time make this method more expensive Extruded bricks – For extruded bricks the clay is mixed with 10–15% water (stiff extrusion) or 20–25% water (soft extrusion) in a pugmill This mixture is forced through a die to create a long cable of material of the desired width and depth This mass is then cut into bricks of the desired length by a wall of wires Most structural bricks are made by this method as it produces hard dense bricks and suitable dies can produce perforations as well The introduction of such holes reduces the volume of clay needed and hence the cost Hollow bricks are lighter and easier to handle and have different thermal properties from solid bricks The cut bricks are hardened by drying for 20 to 40 hours at before being fired The heat for drying is often waste heat from the kiln