30 ANNUAL REPORT 
The following table taken from the “Directory of American Cement 
Industries,” being the result of a series of tests made at the Holyoke 
Dam, Massachusetts, and supplemented by some of the writer’s tests,- 
shows the effect of adding sand to cement in reducing the strength of the 
mortar. All tests were tensile tests upon mortar briquettes 28 days old, 
made from high grade American Portland cements. 
The results of the Holyoke test are given in column number 3 and 
the writer’s tests in column number 4. 
TABLE 6. 
Strength of Various Grades of Mortar. 
Cement. Sand. Tensile Strength. 
Pounds per square inch. 
1 2 3 4 
neat 0 889 73 
1 1 805 581 
I ie: 589 428 
i 3 348 275 
1 4 204 211 
1 5 133 161 
1 6 121 
! 7 val 
1 8 53 
l 9 44 
EFFECT OF WATER UPON THE STRENGTH OF MORTAR. 
Another feature plainly noticeable in mortars is the effect of the 
proportion of water used upon the strength of the mortar. Too much 
or too little water greatly reduces the strength of the mortar. Each 
sand and each cement influences the amount of water necessary to make 
the strongest mortars. In general, fine sands and loamy sands require 
more water than coarser and cleaner sands. Natural cements require 
more water than Portland cements. Mortars of 1 sand to 1 cement re- 
quire more water than mortars having greater proportions of sand. Too 
little water making a stiff mortar, will increase the cost of working with 
it during construction and will decrease the perfect crystallization, 
thus decreasing the strength. Too much water acts as a dilutant, leaving 
the mortar porous when hardened and consequently not so strong as 
dense mortar. When mortar is placed where it will get very little ad- 
ditional moisture over that used in mixing it, sufficient water should be 
used to thoroughly hydrate the cement. 
The writer in making laboratory tests found that a set of briquettes 
made from standard sand and Portland cement with 12% per cent. of 
water, lost one-sixth of the water in the 24 hours that the briquettes 
remained in the air, although they were covered with a dampened cloth. 
