Rain damaged concrete causing dusting

Hi all,

We had concrete included around the perimeter of our house as part of our new build, including paths and a patio under pergola.

The patio slab is dusting and parts of the cove finish can be rubbed of with just my hand.

We have received conflicting advice about how to remedy it. Independent concretor says surface needs to be gound down before any resurfacing or rectification. Concretor who did the job wants to use hardener and then resurface (product looks a bit like render).

Any suggestions on how to remedy this? We are overall really unhappy with the job. It's rough all round and we already compromised with the contractor as our drveway ended up two different colours!

Thanks heaps!