BEICKS AND BEICKMAKING 11 



As the amount of this shrinkage varies for different brick earths, the 



contraction to be allowed for can only be determined experimentally, 



for the particular earth 



being used. The size of 



an ordinary brick is 9" 



by 4§" by 3". Eoughly Fig. 2. 



approximate allowances 



for contraction would be ^ incn on the leEgth, a full \ inch on the 



width, and a full \ inch on the thickness. 



The mould illustrated is triple, that is it moulds three bricks at 

 a time. The strip of wood which forms the bottom should be at least 

 \ inch narrower than the inside width of the mould, so as to leave an 

 opening at least \ inch wide along each side of the bottom. These 

 openings allow the air, which is displaced by the brick earth being 

 pressed into the mould, to escape. The mould illustrated in Fig. 2 is 

 drawn bottom upwards, to show this. 



Bricks moulded by hand in this way may easily be provided with 

 a frog, or indentation, on one face, by nailing a piece of wood of the 

 required shape and size to the bottom of the mould. The frog forms 

 a key for the mortar when the bricks are built in place. 



Bricks may be hand-moulded by either of two methods, called respec- 

 tively " slop moulding " and " sand moulding," according to the procedure 

 which is adopted in order to prevent the brick earth from adhering to the 

 mould. 



In Slop Moulding the mould is dipped in water before moulding each 

 set of three bricks. Tins method is open to the objection that it is apt 

 to cause the bricks to crack and twist while they are drying. 



Sand Moulding is the better method; the inside of the mould is 

 sprinkled with fine dry sand each time a set of three bricks is to be 

 moulded. 



In this connection it may be mentioned that lining the mould with 

 sheet zinc, or flat galvanised iron, allows the bricks to leave the mould 

 very cleanly and easily. 



The brick earth should be thoroughly pressed and kneaded into the 

 mould by hand, and then straightened, or struck off on the upper surface 

 with a " straight-edge " or " strike " till flush with the top of the mould. 



Drying. — The mould is then taken up in both hands and carried to 

 a level piece of ground, that has been previously prepared by clearing 



