CHAPTER II 



BRICKS AND BRICKMAKING 



On nearly all farms earth suitable for the manufacture of bricks can 

 be found. 



In South Africa the sun-dried brick is employed to a great extent, 

 but it is much better to make and use the burnt brick; the extra 

 cost of the burning process amounts to only a few shillings per 

 thousand bricks. 



Brick Earth. — This is the name given to the earth from which 

 good burnt bricks can be made. A suitable earth has been found to 

 be a loam (i.e. a mixture of clay and sand) consisting of about 4 parts 

 clay to 1 part sand. Pure clay is not suitable for brickmaking. It 

 shrinks, cracks, and twists too much while the bricks are being dried 

 and burned. The presence of sand, in about the above proportion, 

 prevents twisting and cracking and lessens the amount of shrinkage ; 

 on the other hand, the presence of too much sand makes the bricks 

 weak and easily broken. 



In addition to clay and sand, a good brick earth should contain 

 materials which promote partial fusion of the brick earth, and which 

 are therefore called Jinxes. Lime, iron oxide, and magnesia, are all 

 fluxes. Fluxes increase the tendency to vitrify, thus partially fusing 

 the particles of brick earth together, and producing a stronger brick. 

 Lime, however, must not be present in too large quantities, or it will 

 cause the bricks to fuse and run out of shape. Most brick earths 

 contain magnesia and iron oxide. The latter is the more favourable 

 to the quality of the bricks produced. The presence of iron is indi- 

 cated by a dark grayish blue colour, in the interior of the finished 

 brick, changing to red at or near the surface. 



Earth containing carbonate of lime (limestone, chalk) should be 

 avoided, because this impurity burns to quicklime, which afterwards 

 tends to absorb moisture and so cause disintegration of the brick. 



