20 BULLETIN 691, U. S. DEPARTMENT OF AGEICULTUEE. 



hot sand and followed by the asphalt. The mixture should con- 

 tain from 9 per cent to 12 per cent bitumen and will vary within 

 these limits with the exact grading of the aggregate. After 

 thorough mixing the hot mixture should be deposited in a 

 uniform layer on a binder course which has been previously 

 laid over a concrete base. It should be laid to such depth that 

 it will yield a uniform layer IJ or 2 inches in thickness as may 

 be required after thorough rolling. 



As a seal coat for tar macadam or tar concrete roads it is 

 applied during construction of the road at a temperature of 

 from 300° F. to 350° F. It is used as a substitute for tar seal 

 coat and may be applied at the same rate and covered in the 

 same manner as described under Specifications TP-2 and TP-3. 



