Structural cracks are repaired by filling the cracks with a high strength epoxy injection resin that bonds fractured concrete back together. The most appropriate injection resin is determined by the width of the crack and its location. Lower viscosity injection resins are best for filling narrow cracksu0097higher viscosity injection resins are better for filling wide cracks. Vertical or overhead cracks usually require sealing the surface with an epoxy gel to insure that the resin doesnu0092t run out before it cures. Some cracks in horizontal surfaces can be filled by gravity feeding epoxy into the cracks.