MANUFACTURE OF PLASTERS. 



51 



Wall-plaster. An ordinary wall-plaster contains, in addition to 

 whatever retarder may be necessary, a certain percentage of finely picked 

 hair or other fiber. In order to insure thorough mixing with the plaster 

 the hair is first picked to pieces in a hair-picker, which is usually a device 

 of the toothed-drum type revolving at high speed. The hair is then 



FIG. 16. Broughton mixer. 

 (Des Moines Mfg. Co.) 



FIG. 17. Hair-picker. 



added to the plaster in the proportions of H to 3 Ibs. hair per ton of 

 plaster and the materials are fed to the mixer. 



The hair-picker shown in Fig. 1 7 is run at a speed of 600 revolutions 

 per minute and will disintegrate 5 to 6 bales of hair per hour. It is 

 listed at $75. 



Wood fiber is often used as a substitute for hair, the cottonwood 

 giving a particularly serviceable fiber for this use. The log is barked 

 by hand or machine and cut into sections 20 inches or so in length. 

 These are then placed in a fiber machine, which will usually take pieces 

 6 to 15 inches in diameter. The fiber is torn off by revolving toothed 



