Repair or rebuild a concrete block wall?
Broken coping, a few damaged blocks or a gate post that's worked loose can usually be repaired without touching the rest of the wall. A wall that leans, has slid or has cracks running through the block itself usually points back to the footing, and no patch on the face fixes that. In that case I'll tell you plainly that rebuilding, starting with a proper footing, is the better spend, because I'd rather fix what caused it than the part you can see.

