344 WATERPROOFING 



is added in the usual manner. Ordinary precautions should 

 be taken to make the concrete dense, and as a rule it is 

 mixed rather wet. 



Metallic Stearates and Other Compounds. Besides the 

 materials mentioned, various other chemicals are used to 

 make concrete waterproof. One of the most successful of 

 these is calcium stearate, which is a salt of a fatty acid. 

 Usually, the quantity of finely ground metallic stearate 

 added to the cement to make the concrete waterproof is 

 about 2% of the weight of the cement. 



Besides the metallic stearates, other substances are used 

 more or less to waterproof concrete by the integral method. 

 A mixture of oil and water has been used with some success, 

 as has also chloride of lime. The purpose of the chemicals 

 is in every case to fill the voids, and, in addition, some of 

 them are water repellants. 



SUPERFICIAL METHOD 



Waxes. To make concrete waterproof, it is sometimes 

 coated with wax. The wax sinks into the pores of the con- 

 crete, filling the voids therein and thus preventing the per- 

 colation of water. 



Paraffin is used for waterproofing with considerable suc- 

 cess. A paraffin especially hardened to resist the sun's rays 

 is used. The concrete surface on which the paraffin is to be 

 applied should be thoroughly dry and not very cold. In fact, 

 it is better to warm the surface with a torch if possible. The 

 paraffin is heated and then applied with a brush. The hot 

 paraffin is absorbed by the concrete, into which it penetrates 

 for a short distance. Paraffin will resist the action of acids 

 and alkalies. 



Instead of applying paraffin while hot, it may be dissolved 

 in some volatile carrier, such as benzine. The dry wall is 

 painted with this solution, which is readily absorbed. The 

 carrier then evaporates and leaves the paraffin to fill the pores 

 in the surface of the wall. If the carrier is inflammable, care 

 must be taken in using it. 



Cements. A common method of waterproofing concrete is 

 to coat the surface of the concrete with an impervious cement 



