VillageLevel Brickmaking 
Appendices 

Before beginning to make the hinge mould you must determine two things. First, what will be the final fired brick size and second, how much does the soil shrink from its moulded to its fired brick state.
Read the chapter on Standardization for information on the best sizes for bricks. Once the fired brick size has been decided, the interior dimensions of the mould can be calculated.
Remember that all brick clays shrink between 5% and 11% when dried and fired. Therefore to arrive at the correct size of brick, the moulds must be 5% to 11% larger than the final size of the brick.
The best way to determine the shrinkage rate for a particular clay is to have a soils laboratory do the testing. This is important especially if the bricks must be produced to a specific dimension. If the final size is not that critical and an error of 5 to 10mm in overall length is not a problem, then the following method can be used to determine the shrinkage rate for a particular brick clay.
1. Make an experimental hinge mould and follow test 4 in Appendix 1. Make 50 or more bricks and fire them in a small kiln.
2. Once fired, randomly select 10 unbroken bricks.
3. Lay the 10 bricks butted up tight against each other, end to end, on a smooth level floor.
4. Measure the overall length of the bricks in millimetres and divide that length by ten. This will give the average length of the bricks.
5. Measure exactly in millimetres the inside length of the mould used to make the bricks.
6. Use the following formula to determine shrinkage rate.
% of Shrinkage =((length of mould in mm)  (average length of bricks)) x 100/(length of the mould in mm)
For example: length of the mould = 258mm average length of bricks = 240mm
% of Shrinkage =(258 mm240 mm)x100/258mm= 18x100/258= 1800/258=7
Shrinkage = 7%
The following table shows, the interior mould sizes for various shrinkage rates to make four different sizes of fired bricks. For example, a village would like to produce a fired brick 240mm x 115mm x 73mm in size and knows that their clay has a shrinkage rate of 8%. In order to obtain that final size, the interior of the mould must be 261 mm x 125 mm x 80 mm.
Table For Interior Mould Sizes 

Fired Brick Size: 240 mm x 115 mm x 73 mm 

Interior Mould Size 

Shrinkage 
length 
width 
height 
5% 
253 mm 
121 mm 
77 mm 
6% 
256 mm 
122 mm 
78 mm 
7% 
258 mm 
123 mm 
79 mm 
8% 
261 mm 
125 mm 
80 mm 
9% 
264 mm 
126 mm 
81 mm 
10% 
267 mm 
128 mm 
81 mm 
11% 
270 mm 
129 mm 
82 mm 
12% 
273 mm 
131 mm 
83 mm 
Fired Brick Size: 230 mm x 110 mm x 70 mm 

Interior Mould Size 

Shrinkage 
length 
width 
height 
5% 
242 mm 
116 mm 
74 mm 
6% 
244 mm 
117 mm 
75 mm 
7% 
247 mm 
118 mm 
76 mm 
8% 
249 mm 
120 mm 
77 mm 
9% 
252 mm 
121 mm 
78 mm 
10% 
255 mm 
122 mm 
78 mm 
11% 
259 mm 
124 mm 
79 mm 
12% 
262 mm 
125 mm 
80 mm 
Fired Brick Size: 220 mm x 105 mm x 66 mm 

Interior Mould Size 

Shrinkage 
length 
width 
height 
5% 
232 mm 
110 mm 
69 mm 
6% 
234 mm 
112 mm 
70 mm 
7% 
236 mm 
113 mm 
71 mm 
8% 
239 mm 
114 mm 
72 mm 
9% 
242 mm 
115 mm 
73 mm 
10% 
244 mm 
117 mm 
73 mm 
11% 
247 mm 
118 mm 
74 mm 
12% 
250 mm 
119 mm 
75 mm 
Fired Brick Size: 210 mm x 100 mm x 63 mm 

Interior Mould Size 

Shrinkage 
length 
width 
height 
5% 
221 mm 
106 mm 
66 mm 
6% 
223 mm 
107 mm 
67 mm 
7% 
225 mm 
108 mm 
68 mm 
8% 
228 mm 
109 mm 
69 mm 
9% 
231 mm 
110 mm 
69 mm 
10% 
233 mm 
111 mm 
70 mm 
11% 
236 mm 
113 mm 
71 mm 
12% 
239 mm 
114 mm 
72 mm 