12 BULLETIN 691, U. S. DEPARTMENT 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. 
