When purchased/implemented the repair crew would systematically (albeit slowly) repair the walls and gates of the tower/keep/castle PROVIDED: 1) there is adequate supply, 2) there are no other upgrades in process, and 3) the tower/keep/castle is not currently ‘under attack’. Repairs would be on a “worst first” basis, meaning that each ‘tick’ the repair crew would work on the wall segment or gate that has taken the most % damage.