A method of manufacturing a plurality of secondary containment panels and assembling and installing the panels in a secondary containment system of an above-ground liquid storage tank or other retention facility includes forming a plurality of flexible substrate pieces. A liquid impermeable coating is applied to the upper surface of each piece such that an edge segment of the piece remains uncoated. The coating is applied to the substrate piece in an indoor enclosure using a computer controlled robotic sprayer that applies a uniform coating. A system for coating secondary containment panels. An apparatus for spraying a coating on a secondary containment panels. The apparatus may be computer controlled and operate automatically to coat the surface of the panel.