I just drywalled my bathroom and placed durock around my tub surround. In the process of getting to room ready for the tile I primed the walls and primed the durock, not knowing I wasn't supposed to. I used a wire brush and attempted to grind off the primer without luck. What can I do to salvage the durock and still be able to tile it?

If you wire brushed it you are ok. Just use a modified thinset when setting the tiles. If you cant get a no-sag mortar you might need a ledger board along the bottom to support the first full row of tile while the thinset sets up overnight. You can keep on tiling by using spacers to support the rest of the rows.