12 BULLETIN 691^ U. S. DEPAETMENT OF AGRICULTURE. 



by the kind and quality of rock used. The application should be 

 followed by a sufficient amount of clean small-sized broken stone 

 to fill the surface voids when thoroughly rolled. A seal coat of 

 the hot asphalt 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 char- 

 acter 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 maintenance treat- 

 ments should be applied whenever the wear comes directly upon 

 the wearing course rock. 



