SPECIFICATIONS FOR WATERPROOFING CONCRETE IN SUBWAYS After concrete is in place and firmly set, surface should be brushed so as to be free from dust, then painted with primer paint, manufactured by (or any paint equal thereto) ; this should beapplied cold with a brush. After paint has become dry, surface should be coated with hot water proofing asphalt, manufactured by (or any asphalt equal thereto) ; this should be applied at a tempera ture of about 450°F. with ordinary roofers' mops. Be fore this coating has cooled, and while still in a "sticky" condition, a layer of asphalt-saturated felt or asphalt saturated burlap should be laid lengthwise with the tunnel; these strips of felt or burlap should be laid so that no more than two rolls end at any one place.
After one layer of felt or burlap has been laid com pletely around the tunnel, the surface of same shall be mopped with the hot waterproofing and the second layer of felt or burlap shall be spread so as to break joints with the first layer. The second strips of
felt or burlap should also be laid lengthwise with the tunnel, and in such a manner that the surface of the tun nel shall have two thicknesses of felt or burlap all over.
The second surface of the second layer of felt or burlap shall be thoroughly mopped with the hot water proofing asphalt to a thickness of about one-eighth inch.
After the asphalt has become cool, an inner ring of Portland cement plaster (1 part cement to 2 parts sand), reinforced with expanded metal, shall be placed over it to a thickness of 2 inches. In this way the tunnel has a complete ring of waterproofing material surrounding it, and is protected by the inner ring of cement plaster.