Pitted metal? I have many times used a big wire cup on my right angle grinder, to try to clean such best I can, I clean the rust dust off, and wipe it down good with Ospho , to be safe, wet again real good with the Ospho and neutralize it with water, air try to keep away flash rust, I give it a day to be sure it is dry in any crack or crevice, and epoxy prime. Never had a problem. Only other way to work that pitted metal would be blast with an abrasive that does not work it. Roofs would work pretty quick I bet.
