30 BULLETIN 246, U. S. DEPARTMENT OF AGRICULTURE. 
The specification already given for concrete curbs constructed in combination 
with the foundation shall also apply to curbs constructed separate from the 
foundation as regards proportioning, mixing, and placing the concrete, con- 
structing the forms, and all other features of construction which are not 
covered on the plans or in this specification. 
STONE CUEBS. 
Where stone curbs are required, they shall be hauled and set before the 
subgrade is finally completed. The curbs shall be set true to line and grade 
and shall be securely bedded in broken stone, gravel, or firm earth. In pre- 
paring the trenches for the curbs great care shall be exercised to see that the 
material upon which the curb is to be set is well compacted, firm, and hard. 
Stone curbing shall be quarried from hard, tough, homogeneous stone. The 
individual blocks shall have the cross section shown on the plans and shall 
be not less than four (4) feet in length. Each block shall be free from seams and 
all other imperfections and shall be neatly dressed and finished on all exposed 
faces. 
CRUSHED-STONE BASE. 
Where a crushed-stone base is called for on the plans it shall be constructed 
after the curbs are set and in two (2) courses of such thickness that the finished 
base will have the required depth shown on the plans. 
The first course of stone shall consist of a single layer of No. 1 stone spread 
uniformly to a depth of not more than eight (8) inches before compacting. The 
stone shall be spread by hand from dumping boards or from dump wagons of a 
type that will distribute each load of stone evenly over that part of the sub- 
grade to be covered by the load. 
After the crushed stone of the first course has been spread to the required 
depth, it shall be rolled until it is thoroughly compacted and firm with a power 
roller of the macadam type, weighing not less than ten (10) tons and not more 
than fifteen (15) tons. The rolling shall begin at the curbs and progress gradu- 
ally toward the crown. All irregularities and depressions that may develop 
shall be immediately corrected with No. 1 stone, and the rolling shall continue 
until the stone is well compacted and the surface is uniform in grade and 
cross section. 
The second course of stone shall consist of a single layer of No. 2 stone 
spread uniformly to a depth not exceeding four (4) inches. The stone shall be 
spread and rolled in the manner prescribed for the first course. When completed 
the surface of the second course of crushed stone shall be smooth, firm, well 
compacted, and continuous, and shall have the cross section and grade indicated 
by the drawings. 
After the second course of stone has been spread, rolled, and completed as 
above specified, screenings shall be spread uniformly over the surface to a depth 
of approximately one-half (!) inch. The spreading shall be done with shovels 
from piles along the road, from dumping boards, or from carts. In no case shall 
an entire load of screenings be dumped directly upon the second course. 
After the screenings are spread they shall be dry rolled until the voids of the 
second course are filled. The foundation shall then be sprinkled with water 
from properly constructed sprinkling wagons and rolled with a power roller of 
the type and weight specified for the first course. The amount of water used 
shall be sufficient to wet the stone thoroughly, but shall be put on in such quan- 
tity and manner as not to wet and soften the subgrade. Screenings shall be 
added and the sprinkling and rolling continued until the surface ceases to show 
