Abstract: A double wall, light-weight tank construction for the storage of flammable liquids is formed from two conventional steel tanks having flame proof, curable cementitious insulative material between the walls. Spacers preformed preferably of the same cementitious material are glued about the exterior surface of a conventional inner tank having ports. An exterior tank is formed with one end cover being detachable. Apertures are cut in the exterior tank to align with the ports of the inner tank when it is in its final nested position within the exterior tank. Stoppers and vents are placed in a sidewall of the exterior tank. Both tanks are oriented vertically, and the interior tank is then lowered into the exterior tank with concentric alignment provided by the spacers. Nipples are then attached to the ports, and rings are placed over the nipples and welded to the nipples and the exterior tank. The detached end cover is welded to the exterior tank.