Is shotcrete applied to hardened cast-in-place concrete considered monolithic by the American Concrete Institute (ACI)? Is shotcrete-to-shotcrete considered monolithic by ACI? Can either of these connections be made watertight? Or at least as watertight as the concrete? Is shotcrete without admixtures truly watertight or waterproof? (My definition of “watertight” would be a measurable amount or more than leaching of moisture and calcium.)

Shotcrete properly applied to a well-prepared existing concrete surface will create an excellent bond and structurally act as a monolithic system without joints or layers. Pulloff testing of shotcrete applied to concrete will often fail in the underlying concrete substrate, and not at the bond interface or within the shotcrete section.
Shotcrete is a method of placing concrete and should have similar watertightness characteristics. These characteristics can be enhanced with admixtures and supplementary cementitious materials such as silica fume. Please refer to the images of cores from shotcrete applied to existing concrete.