STATE GEOLOGIST. 37 
b 
“Directory of American Cement Industries ;’ and number three is taken 
from Professor J]. O. Baker’s “Roads and Pavements.” They seem to 
have the same general origin. 
TABLE 7. 
Materials used in Coloring Mortars. 
| (Pounds Color 
Pounds of Color to 
| 100 Pounds Cement. to Barrels 
' Color. | Mineral. _ Oemneiat. 
Grayge i ca Germantown Lamp Black....... le eee ye | 2 
BIaCki he eee Manganese Dioxide.............. fx! BORD at Eat a aa | 48 
Blacker ti xcelsion@arbon black=.) ..25 >. Meter 2 seers Renesas 
BlUCwe ae. heap Wiltramarine i fen. oa oes sehr: 5 5 to 6 | 20 
Greeny. OX. Ultramarine Green.............. 6 6 | 24. 
EVO GG ere cone: ron Oxi erty yer. treany ese 6 6 to 10 | 24 
Bright Red....| Pompeian or English Red........ 6 6 | 24 
Sandstone Red. | Purple Oxide of Iron ............ 6 preety ele ice 24 
Wioletin.. fe. . WioletOxide of iron arene Grose | 24 
IBIROMVL. gba gocn Roasted IronOxide or Brown Ochre 6 6 al 24 
Yellow or Buff | Yellow Ochre ................ 6 6 to 10 | 24 
Wives Lime, White Sand and Marble, also a Mixture of Lead and 
Re se een Zinc Salts with Calc Spar will give very light surfaces. 
The color is mixed in various ways. In concrete walks it is some- 
times sprinkled on the top and troweled into the surface. This does not 
give an even color nor does it last as well as when thoroughly incor- 
porated with the sand and cement. It is sometimes added to the sand and 
thoroughly mixed dry, then the cement and finally the water is added. 
The best method is to mix the coloring matter and cement dry, and use it 
thereafter as so much cement. Strength is gained and expense saved by 
using the colored cement for the surface coating only, not exceeding one 
inch in depth with the colored mortar used. 
The effects in the red and brown sandstones are imitated so perfectly 
that it requires close inspection to detect the artificial from the natural 
stone. The artificial stone, however, is more durable and stronger than 
the natural stone. 
HAIR CRACKS OR SUN CRACKS. 
The surface of concrete sidewalks, and the smooth finished surfaces 
of other cement or concrete structures, frequently exhibit a network of 
fine cracks variously called sun-cracks, hair-cracks, veins and crazed work. 
There appears to be a variety of opinions as to the cause of these 
veins or cracks. A summary of the answers received to the question 
“What causes sun-cracks or hair-cracks?” may not be out of place. These 
answers were received from experienced cement workers, engineers and 
cement manufacturers. Twelve gave as a reason, that the surface coating 
Was too rich in cement. One, that too fine sand caused the trouble, bring- 
ing too much cement to the surface. Three, that over troweling was 
