BRICKS AND BMCKMAKING 



17 



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which form in the dagga plaster as it dries, in fact it may be necessary 

 to plaster up some of these cracks so as to control the combustion. 



The clamp is allowed to burn for four or five days, by which time the 

 bricks should be sufficiently fired. Combustion is then stopped by com- 

 pletely closing the ends of the kindling fire-places, and plastering all 

 cracks, and also the top of the 

 clamp, with dagga to exclude air. 

 The clamp is then allowed to stand 

 for about ten days, to cool off, 

 before the bricks are removed. 



Wood-firing. — In cases when 

 coal is not available as a fuel, 

 wood may be substituted. Since, 

 when wood is used, the fires must 

 be replenished frequently during 

 the burning of a clamp, it would not 

 be suitable to distribute the fuel 

 throughout the clamp, as has been 

 described for coal. The wood must 

 be concentrated in fuel chambers. 

 A clamp suitable for wood-firing 

 is shown in Fig. 9. The bricks 

 composing it are built close-packed 

 on edge, the lengths of the bricks 

 in any one course crossing the 

 lengths of bricks in adjacent 

 courses at right angles. Two fuel 

 chambers, F, running from end to 

 end of the clamp, are left, being 

 closed over on top by corbelling 

 the bricks. These fuel chambers 

 are packed carefully with fuel, 

 while the clamp is being built. The fuel should consist of logs, not 

 less than 4 inches in diameter, with chips underneath for kindling. 

 The sides of the clamp are plastered with dagga and a layer of ashes 

 is laid on top. The fires are then ignited, and the ends of the fuel 

 chambers bricked up and smeared with dagga, as for coal-firing. The 

 fires must be stoked, at least three times every 24 hours, with logs 



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Fia. 9. — Clamp for wood firing. 



