58 



CEMENTS, LIMES, AND PLASTERS. 



Slosson and Moudy on Laramie plaster, a bushel weighed 64 Ibs., and 

 a block composed of 50 parts sand and 100 parts plaster, after being set 

 and dried, gave a specific gravity of 1.5, corresponding to a weight of 

 93^ Ibs. per cubic foot. 



Fineness of calcined plasters. A number of cement plasters, wall- 

 plasters, and allied products from Iowa, Kansas, Texas, and Oklahoma 

 were tested for fineness by Prof. Marston in 1900. The results* of these 

 tests are given in the following table. The tests were made on mate- 

 rial purchased in the open market. 



TABLE 12. 



FINENESS OF CALCINED PLASTERS. 

 Per cent passing sieve. 



Tensile and Compressive Strength. 



Methods of testing plasters and similar products have never been 

 standardized, and the result is that each investigator applies such 

 tests as he may deem advisable. In general the practice has followed 

 closely along the lines of cement-testing. 



Tensile strength of plasters. In making the experiments discussed 

 below, Professor Marston "mixed the plaster or stucco thoroughly, 

 by hand, with water. The mortar was then placed in standard (Am. 

 Soc. C. E.) cement briquette molds and packed with the finger. The 

 surface of the briquette was smoothed with a trowel. As soon as the 



* Iowa Geological Survey, vol. 12, p. 162 



