60 



CEMENTS, LIMES, AND PLASTERS. 



The results of a later series of tests carried * out by Prof. Marston 

 are given below. Most of the tests were made on fresh plaster as mar- 

 keted. A few, however, noted in the table as "sifted", were made on 

 that portion of the plaster which passes through a 100-mesh sieve. 

 Plaster four years old was also tested, as noted in the table. All the 

 figures given are the averages of from 3 to 15 separate tests. 



500 Ibs. 



40011)8. 



FIG. 18. Effect of sand on tensile strength of plasters. (Marston.) 



These tests appear to show f that 



(a) Cement plasters and stuccos attain almost their full strength 

 at the end of one week, showing little further gain at three months. 



(&) The portion of the plaster which passes a 100-mesh sieve is 

 stronger than the coarser portions, and the higher strength of fine plaster 

 is shown better in sand mixtures than when tested neat. 



(c) The value of fine grinding is further emphasized by the high 

 results shown by the German stucco, which seems to have been the 

 most finely ground of all, though the values of fineness given are not 

 quite consistent. 



* Iowa Geol. Survey, vol. 12, pp. 232-235. 



t The conclusions here drawn from these tests are those of the writer. For 

 Professor Marston's conclusions, which do not entirely agree with mine, reference 

 should be made to the original work. 



