Curbs and Gutters

The curb should be set with a uniform batter, in a straight line, and on a regular grade. To fulfill these conditions requires careful work in the first place, and to prevent the curb from subsequently getting displaced requires proper design and thorough workman ship. The trench in which the curb is to be set should be dug 4 to 6 inches below the base of the curb to allow for a layer of gravel on which to set the stone; and the width of the trench should be at least three times the thickness of the curb to allow room for ram ming the earth around the stone. The bottom of the trench should be made smooth and be thoroughly consolidated by ramming, and the gravel also should be compacted. Where gravel is expensive, it is dispensed with, the curb being set upon brick or stone. In filling the trench, the earth should be thoroughly rammed in layers not more than 4 inches thick. Where gravel is plentiful, it is sometimes specified that the trench shall be filled with gravel to 8 or 10 inches from the top.

In the past there has been so much trouble in keeping curbs in line, that within recent years there has been a general tendency to set the curb in a bed of concrete—particularly when concrete is used for the foundation of the pavement. A 6-inch layer of con crete is deposited in the trench and the curb set upon it, after which the trench is filled with concrete on the street side up to the base of the proposed pavement and on the back side nearly up to the top of the curb. When set in concrete, the curb does not need to be as

deep as otherwise, since the concrete then practically becomes a part of the curb.

Cost.In most localities, split sandstone or limestone curbing 4 to 5 inches thick can be had for 20 to 25 cents per square foot f. o. b. cars at the destination; and often sawed stone can be had at about the same price. The additional cost of a bush-ham mered or axed surface will vary with the hardness of the stone and the degree of the finish, and curves will cost 30 to 50 per cent more than straight pieces. Hudson River bluestone (sandstone) curbing costs from 20 to 40 cents per square foot.

Granite curb costs from 25 to 50 cents per square foot, de pending upon locality and thickness.

Concrete

Curb. In some sections where suitable stone for curbing is not readily available, curbs have been made of Port land-cement concrete. Owing to the decreasing price of cement, this form of curb will doubtless come into more common use. It is usually made about 6 inches thick and 18 or 20 inches deep. If well made, it does excellently for residence streets.

For suggestions concerning the construction of concrete curb, see § 523-27.