I have seen this done on older farm homes in MO. All they did was to power wash the existing wall to remove all the dirt and grime, then float on concrete.
Now, this will crack and fall off in areas, so this is something that will have to have periodic maintenance done. Temp changes will cause this and water getting in there and emploding the concrete.
You might consider installing some metal lathe on the rocks and spray cement on this then trowel or float it out and have a done deal.
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