Can this be used to repair a large gap in an old basement retaining wall? It's about 2 feet in width, 1 foot high, and varying from 1/2 inch to 4 inches in depth.

Polymer Modified Structural Repair can work for your application but it can only go to 2" deep at one time. Please wait 6 hours and then you can do a second 2" layer to reach 4". For further assistance please call 1-800-282-5828