Polyurethane grouting contractor, Sub-Technical, Inc., injects a dense polyurethane grout into the roof of a hard rock mine. This process solidifies and secures the roof to prevent collapse when less than ideal conditions are encountered. The polyurethane used was Purock 70, which is a dual component, high density, ground control grout. It has a compressive strength of over 12000 psi and a shear strength of over 6000 psi, which is achieved in minutes.