220 



POPULAR SCIENCE MONTHLY. 



to the surface, but also, when properly set and dried before the surface is 

 laid, keeps the surface as free as is possible under the circumstances 

 from ground water, and thus contributes to the longevity of the sur- 



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The concrete surface, having been laid as nearly as possible of the 

 proper contour, and having been thoroughly set, dried out and swept 

 clean, is covered with a binder course to fill the inequalities of the con- 

 crete and form a bond between the concrete and surface that will 



