26 BULLETIN 691, U. S. DEPARTMENT OF AGRICULTURE. 
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 same bituminous material should then be ap- 
plied 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 the methods given 
under specifications OC-2 or OH-1. The latter is usually to be 
preferred. Such maintenance treatments should be applied when- 
ever the wear comes directly upon the wearing course rock. 
