24 
BULLETIN 949, IT. S. DEPARTMENT OE AGRICULTURE. 
(41) The consistency of standard mortar shall depend on the amount of water 
required to produce a paste of normal consistency from the same sample of cement. 
Having determined the normal consistency of the sample, the consistency of standard 
mortar made from the same sample shall be as indicated in the following table, the 
values being in percentage of the combined dry weights of the cement and standard 
sand. 
Percentage of water for standard mortars. 
For 1 to 
| 
For 1 to 
Fori to 
Fori to 
For 
3 mor- 
For 
3 mor- 
For 
3 mor- 
For 
3 mor- 
neat 
tars of 
neat 
tars of 
neat 
tars of 
neat 
tars of 
ce- 
stand- 
ce- 
stand- 
ce- 
stand- 
ce- 
stand- 
ment 
ard Ot- 
: ment 
ard Ot- 
ment 
am Ot- 
ment 
ard Ot- 
paste. 
tawa 
1 paste. 
tawa 
paste. 
tawa 
paste. 
tawa 
sand. 
sand. 
sand. 
sand. 
18 
9.5 
21 
22 
10.0 
10.2 
24 
25 
10.5 
10.7 
27 
28 
11.0 
19 
9.7 
11.2 
20 
9.8 
23 
10.3 
26 
10.8 
29 
11.3 
DETERMINATION* OF SOUNDNESS. 
(42) A steam apparatus, which can be maintained at a temperature between 98° 
and 100° C, or one similar to that shown in figure 11, is recommended. The capacity 
of this apparatus may be increased by using a rack for holding the pats in a vertical 
or inclined position. 
(43) A pat from cement paste of normal consistency about 3 inches in diameter, 
one-half inch thick at the center, and tapering to a thin edge, shall be made on clean 
glass plates about 4 inches square, and stored in moist air for 24 hours. In molding 
the pat, the cement paste shall first be flattened on the glass and the pat then formed 
by drawing the trowel from the outer edge toward the center. 
(44) The pat shall then be placed in an atmosphere of steam at a temperature 
between 98° and 100° C. upon a suitable support 1 inch above boiling water for 5 hours. 
(45) Should the pat leave the plate, distortion may be detected best with a straight- 
edge applied to the surface which was in contact with the plate. 
DETERMINATION OF TIME OF SETTING. 
(46) The following are alternate methods, either of which may be used as ordered : 
(47) The time of setting shall be determined with the Vicat apparatus described 
in paragraph 39 (see fig. 10). 
(48) A paste of normal consistency shall be molded in the hard-rubber ring G as 
described in paragraph 40, and placed under the rod B, the smaller end of which 
shall then be carefully brought in contact with the surface of the paste, and the rod 
quickly released. The initial set shall be said to have occurred when the needle 
ceases to pass a point 5 mm. above the glass plate in one-half minute after being re 
leased; and the final set when the needle does not sink visibly into the paste. The 
test pieces shall be kept in moist air during the test. This may be accomplished by 
placing them on a rack over water contained in a pan and covered by a damp cloth, 
kept from contact with them by means of a wire screen; or they may be stored in a 
moist closet. Care shall be taken to keep the needle clean, as the collection of cement 
on the sides of the needle retards the penetration, while cement on the point may 
increase the penetration. The time of setting is affected not only by the percentage 
and temperature of the water used and the amount of kneading the paste receives, 
but by the temperature and humidity of the air, and its determination is therefore 
only approximate. 
