Disclosed is a method, process and system for sealing cracks in concrete substrates such as walls and floors. A plurality of holes are drilled through the concrete substrate, with at least one hole on each opposing side of the crack. Then a polymer rubber gel that is thick enough to not flow at room temperature (e.g. comprising 99% solids) is heated in a tank to an elevated temperature (e.g. 120-200° F.). Next, the heated polymer rubber gel is pumped in the heated state through one of the holes in the concrete. The pumping continues until the polymer rubber gel is observed exiting a second drilled hole that is spaced apart from the injecting hole. The polymer rubber gel rapidly cools and solidifies, thereby forming a waterproofing membrane that seals the crack(s).