342 WATERPROOFING 



is called to the fact that the spandrel wall cannot be carried 

 up at the time that the lintel and slab forms are filled, 

 especially if wet concrete is used. Therefore, the concrete 

 must first be deposited to the level of the top of the slab, 

 and when this has its initial set, the balance of the wall 

 may be filled. If this precaution is not taken, the hydro- 

 static pressure of the wet concrete in the spandrel wall will 

 force the concrete from underneath the form at the slab and 

 prevent the filling of the wall form. 



Cornice Construction. In Fig. 16 is shown a typical form 

 construction for a reinforced -concrete cornice. The cornice 

 work is carefully constructed of If -in. -dressed material. 

 In filling the form, the concrete is carried to the level A A, 

 and the parapet wall is afterwards constructed above this 

 point. 



WATERPROOFING OF CONCRETE 



CLASSIFICATION OF SYSTEMS 



There are three principal methods, or systems, employed 

 in the waterproofing of concrete. They may be termed the 

 integral, the superficial, and the membrane method. 



The integral method consists in adding something to the 

 concrete when it is placed, or in mixing the concrete in cer- 

 tain proportions, so as to make it waterproof throughout. 

 The superficial method consists in coating the concrete with 

 paint or some other material. This material adheres to the 

 concrete and hardens, or dries, on it. The membrane 

 method consists in putting on the concrete a coating that is 

 distinct from it. While the coating may adhere to the con- 

 crete, it does not crack when the concrete cracks, but is in 

 a distinct membrane usually strengthened by felt or some 

 other fiber cloth. 



INTEGRAL METHOD 



Mixing of Concrete. According to some authorities, if 

 concrete is properly mixed, it will be impervious to water. 

 The exact mixture to use will depend on the quality of sand 



