26 BULLETIN 230, U. S. DEPARTMENT OF AGRICULTURE. 



bars is not seriously weakened by the addition of oil in amounts up to 

 10 per cent. 



Note. — A public 'patent has been granted for mixing oil with Port- 

 land cement concrete and hydraulic cements giving an alkaline reaction, 

 and therefore anyone is at liberty to use this process without the pay- 

 ment of royalties. 



Caution. — The addition of any waterproofing or damp-proofing agent to cement mortar or concrete is 

 valueless unless extreme care is exercised in proportioning, in mixing, and in placing the concrete. 



o 



