Complete restoration, waterproofing and chemical protection of extremely deteriorated digesters. The structure before repair is shown in Figure 1.The existing digester walls were used as forms with reinforcing mesh being mechanically fastened to the exterior and interior of the tank. An additional 10 cm (4”) of Spray-Con WS ST wet shotcrete, mixed on site was applied to the interior and exterior of the tanks, shown in Figure 2.The interior of tanks was coated with two coats of Cem-Kote Flex CR as protection against the sulfuric acid generated by micro-biological conversion of H2S.The exterior of the structure was coated with Cem-Kote ST White. The project was carried out in 1999 and several inspections have shown no deterioration of the protective Cem-Kote Flex CR coating.