A good thing to try are commercial nonshrink mortars for all patch jobs. If the hole extends through the section or if large volume of patching material is needed use concrete for replacement only, rather than mortar. Also, include some white cement in the patching mix because most patches appear darker than the surrounding concrete. Prepare only as much patching material as you can use in about 20 minutes at 70 degrees F. If possible, use an electric saw to square cut or slightly undercut edges. And use gad points and saw-tooth bits rather than chisel points to remove unsound material. Remember the six basic requirements for a lasting concrete patch: (1) good bond; (2) no cracks; (3) impermeable patching material; (4) freeze-thaw resistance, where needed; (5) high early strength, where required; and (6) color and texture matching that of surrounding concrete. Remember also to throughly cure all patches and carefully inspect repair work. Some precautions: don't try short-cuts; don't start patching work on structures in use before determining the reason for deterioration and correcting it, if possible; when using an epoxy to patch concrete, be careful to avoid its toxic effects on certain people when touched or inhaled; don't strike off ordinary patching materials (other than the commercial nonshrink types) level with surrounding concrete. Use a shim to raise the strike-off board slightly above the surface. Also, don't retemper patching materials.