Systems and methods for safely repairing potable water tanks when submerged within a tank. The barrier may be shield structure defining a cavity and having an aperture and valve for injecting the coating material into the cavity, or the barrier may be a sheet preloaded with coating material and stored within and delivered via a transfer shield, or the barrier may be a continuous sheet delivered over the top of the coating material at the same time it is applied. The barrier layer, be it a shield structure sheet or continuous sheet, becomes adhered to the substrate being repaired so post cure removal is not required. Methods of repair include pressing the sealing edge of a barrier shield over an area, injecting coating material between the barrier shield and area, removing the source of coating material, and permitting the coating material to cure.