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BULLETIN 246, U. S. DEPARTMENT OF AGRICULTURE. 



granite and sandstone are probably more used for curbs than any 

 other kind of stone. 



All stone curbing should be hauled, distributed, and set before the 

 subgrade is completed. The individual blocks should be not less 

 than about 4 feet long, except at closures, and should ordinarily have 

 a depth of from 16 to 24 inches, depending on soil conditions and on 

 whether the curb is to project above the surface, forming one side 

 of the gutter. The neat thickness need never be greater than 8 

 inches and, where the traffic conditions are not severe and the quality 

 of the stone is good, a thickness of 6 inches will ordinarily prove 

 satisfactory. Stone curb should always be set on a firm bed of 

 gravel, slag, or broken stone, not less than 3 inches thick, or on 

 unusually firm earth, and should be provided with a backing of the 



WW/7£0 Bft/C/f-) 



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Fig. 1. — Proper method of constructing stone curb. 



same material on the shoulder or sidewalk side. Figure 1 shows a 

 t} r pical stone curb in place. 



Where suitable stone is not readily available or when from any 

 cause the cost of stone curbing would prove excessive, a curb con- 

 structed of Portland cement concrete may frequently be advan- 

 tageously used. Concrete curbs may be constructed alone or in com- 

 bination with either a concrete gutter or a concrete foundation. 

 When constructed alone they should have approximately the same 

 cross-sectional dimensions as stone curbs and should be constructed 

 in sections about 8 to 10 feet in length. Figures 2 and 3 and Plate I 

 show the three common types of concrete curbs. 



Vitrified clay curbing should be set in much the same manner as 

 that described for stone curbing. The principal additional require- 

 ment is that, since vitrified clay is a lighter material than stone and 



