In making briquets by hand, the mortar may well be packed into the molds by the fingers, which should be protected by rubber tips. When the mold is filled and slightly heaped, the trowel should be placed on top, and the molder put about 60 pounds pressure on the trowel. The excess mortar is then cut off by the trowel and the top of the briquet is smoothed by drawing the trowel across the face. The results obtained by four molders using this method in the same laboratory are given in Table 33.

188. The recent progress report of the Committee of the American Society of Civil Engineers on uniform tests of cement contains the following, under "Molding":

"Having worked the paste or mortar to the proper consistency, it is at once placed in the molds by hand.

"The Committee has been unable to secure satisfactory results with the present molding machines; the operation of machine-molding is very slow, and the present types permit of molding but one briquet at a time, and are not practicable with the pastes or mortars herein recommended.

Table 33. Results Obtained By Different Molders When Using Similar Mortar

Ref.

Sand-Parts to One Cement.

water

(63° to 66° F).

per cent dry ingredients.

Temperature of Air where Gaged.

Age.

Mean

Tensile

Strength.

Molder N.

Mean

Tensile

Strength.

Molder M.

Mean

Tensile

Strength.

Molder T.

Number Averaged for Each Molder

Date.

Weather.

a

b

c

d

e

f

g

h

i

1

2 3 4 5 6 7 8 9 10 11

12 13 14 15 16 17 18 19

0 0 1 1 1 1 2 2 3 3

Sum of Means

0 0 1 1 1 1 2

Sum of Means

31.6 "

18.7

" "

15.2 "

13.3

"

31.6

"

18.7

"

" "

15.2

62-65

"

67-62

63-68 "

70-65 "

65-61 "

62-65

"

65 "

" "

67

7 days 28 "

7 " 28 "

3 mo.

1 year 28 days

3 mo.

3 mo.

1 year

7 days 28 "

7 " 28 "

3 mo.

1 year 28 days

81 197 79

235 515 558 196 423 253 260 2797

92 213

91 257 541 569 186 383 263 232 2827

Molder s.

60 145

67 223 435 504 182 1616

89 220

89 259 519 555 197 406 239 236 2809

Molder T.

60 167

71 211 449 491 179 1628

5 5 5 5 5 5 5 5 5 5

5 5 5 5 5 5 5

10-22 10-28

Clear Cloudy

Cement, Brand Gn, Sample 21 R. Sand, Crushed Quartz 20 to 40. All briquets in same line received same treatment after made and were immersed in same tank until broken. 1 Mean of ten specimens.

"method. The molds should be filled at once, the material pressed in firmly with the fingers and smoothed off with a trowel without ramming; the material should be heaped up on the upper surface of the mold, and, in smoothing off, the trowel should be drawn over the mold in such a manner as to exert a moderate pressure on the excess material. The mold should be turned over and the operation repeated.

"A check upon the uniformity of the mixing and molding is afforded by weighing the briquets just prior to immersion, or upon removal from the moist closet. Briquets which vary in weight more than 3 per cent, from the average should not be tested".

189. Marking The Briquets

The briquets made in a given laboratory should be numbered consecutively, so that no confusion can arise, and this one number is all that should be placed on the briquet. The record of the brand of cement, the proportions used, etc., should be placed in a book opposite the briquet number. The briquets should be numbered on the face, near the end. Steel stamps furnish a ready means of numbering, and when mortar contains more than two parts of sand to one of cement a thin strip of neat cement paste plastered across one end of the briquet will aid in making the numbers legible.