102 Bulletin 86 



waterproofing 



Machine-made cement pipe is impervious at ordinary pressures ; 

 no waterproofing is necessary for it. 



Hand-made pipe usually leaks when first put into use, but the 

 leakage decreases gradually and finally ceases. The original leak- 

 age depends upon the proportions of the mortar, the consistency, 

 and the thoroughness of mixing and tamping. It is customary to 

 paint the inside of the pipe with a w^ash made of cement and water 

 to reduce the seepage. 



Hydrated lime is effective in waterproofing concrete but is sel- 

 dom used in pipe manufacture. The Cement Pipe Company of 

 Phoenix have used it in both machine and hand-made pipe. They 

 use 10 pounds per sack of cement. In case the pipe will be under 

 considerable pressure this amount should not be exceeded, and per- 

 haps 8 pounds is a safer limit. In the tests of 1907 the author made 

 pipe with mixtures in which a heavy percentage of lime was de- 

 pended upon in part for the strength of the pipe. At present prices 

 there is no economy, however, in the substitution of lime for cement. 

 There is another advantage in the use of hydrated lime in hot 

 weather, in that the mortar holds water better and the pipe is more 

 readily cured. Tar compounds have not been used for waterproof- 

 ing cement pipe. 



