Abstract: To permit monitoring of tightness of a tank, particularly buried tanks for highly flammable or explosive liquids such as gasoline, flammable hydrocarbon solvents, acids, alkaline solutions and the like, and prevent formation of sparks due to electric charge of an inner liner, the inner surface of the tank has an embossed aluminum foil applied thereagainst, the inner surface of which has an epoxy layer (19) applied thereto by spraying, so that the depressions opposite the corrugations or projections (17) of the foil (15) will be filled with the epoxy. After curing, the epoxy layer (19), preferably fiber-reinforced, is tested for freedom from pores and proper thickness by standard spark induction and eddy current testing methods, and then has another resin layer, preferably epoxy, applied thereto which is made electrically conductive by additives of metal, or carbonaceous granules, flakes or fibers, such as aluminum, nickel, copper brass or of graphite.