28 BULLETIN 691, U. S. DEPARTMENT OF AGEICULTURE. 



form layer over a concrete or well compacted broken stone or 

 gravel foundation to such depth that it will yield a uniform layer 

 2 inches in thickness after thorough rolling. A seal coat of the 

 same bituminous material should then be applied at the rate of 

 0.4 to 0.6 gallon per square yard and covered with a sufficient 

 amount of stone chips to just absorb the excess bitumen. Roads 

 of this character may be maintained with oil surface treatments 

 using the materials and methods given under Specifications OC-2 

 or OH-1. The latter is usually to be preferred. Such mainte- 

 nance treatments should be applied whenever the wear comes 

 directly upon the wearing course rock. 



