=Surface Method.=--The surface method is one in which the gravel is placed on the graded earth road surface without earth shoulders to hold the gravel in place. It is also sometimes called the feather-edge method. Except for the manner of placing as just mentioned, the several operations are conducted in the same general manner as for the trench method. The gravel does not compact as quickly as in the trench method and a considerable loss of material is likely to result from the effect of automobile traffic while the gravel is loose. But it has the advantage of being free from difficulties in wet weather and in some locations is therefore preferable to the trench method. It is particularly applicable to those projects on which the placing of gravel continues throughout the winter, the gravel being dumped and spread, to be finally smoothed and finished in the early summer. =Bonding.=--Where gravels deficient in binder are utilized, clay for binder is sometimes added as the gravel is placed on the road. This may be done by spreading the clay on top of the lower course of gravel, placing the upper layer and sprinkling and rolling until the clay squeezes up through the surface layer. It may also be accomplished by spreading dry clay on the upper course before it is harrowed and then harrowing to mix it with the gravel. Both methods are practiced, but the former is believed to be preferable. A third method is to separate the sand and pebbles and to mix the clay binder with the sand and then spread the sand on top of the pebbles and mix by harrowing. =Maintenance.=--Gravel surfaces require careful maintenance, especially during the first season the road is used. The gravel will compact slowly and during the process will be rutted and otherwise disturbed by traffic. It is important during this period to restore the shape once a week or at least twice a month. The light blade grader is usually employed for the purpose so long as the gravel is somewhat loose. Later a drag of the type known as the planer will prove to be the most effective. Figure 16 shows a type of drag that is very satisfactory for use on gravel roads. [Illustration: Fig. 16.--Road Planer] CHAPTER VII BROKEN STONE ROAD SURFACES The broken stone road surface, or macadam road as it is usually termed, consists of a layer of broken stone, bonded or cemented together by means of stone dust and water. The surface may or may not be coated with some bituminous material. =Design.=--It has been an accepted assumption that the macadam road surface is somewhat more stable than the gravel road surface of equal thickness, and since this is probably the consensus of opinion of engineers familiar with both types, it may be accepted until experimental data are available on the subject.