Polyurea Coating for Digester Tank

Introduction

A water utility client's anaerobic digester tank had developed water and gas leakage alongside chemical degradation to the interior lining. External walls showed active carbonation-induced corrosion. Full removal of the existing coating system was required, with replacement by a chemical-resistant, gas-tight lining across both internal and external surfaces.

Our Solution

Surface preparation was carried out to NACE/SSPC-SP13 standard. Tank internals were high-pressure water jetted at 18,000+ psi to remove laitance and debris, followed by abrasive blasting to eliminate residual coating, a water-based degreaser application, and a final high-pressure wash. New concrete casting had introduced surface voids; these were addressed using a rotary diamond wheel to grind high spots, followed by spray-applied polymer resurfacing compound to restore a uniform substrate profile.

Internally, a monolithic pure polyurea coating was spray-applied, providing a flexible, chemical-resistant, gas-tight membrane. Externally, a three-layer anti-carbonation system — primer plus two heavy topcoats — was applied at 5,000 psi post-jet, delivering waterproofing, elongation capacity, and long-term resistance to carbonation-driven degradation.

Key Benefits

• Gas-tight integrity restored — monolithic polyurea eliminates water and gas permeation pathways
• Chemical resistance — pure polyurea provides robust protection against aggressive digester chemistry
• Surface voids eliminated — polymer resurfacing compound ensured a continuous, defect-free bond surface
• Carbonation protection — three-layer exterior system prevents further concrete degradation
• Elongation capacity — coating flexes with structural movement, reducing risk of cracking or delamination
• Preparation to NACE/SSPC-SP13 — verified surface cleanliness for maximum adhesion performance
• Extended service life — system designed to significantly reduce maintenance frequency and tank downtime

Conclusion

UCL Ltd returned the digester tank to full operational integrity through a correctly specified, rigorously prepared polyurea coating system. This project demonstrates our capability to specify and apply high-performance protective coatings in demanding wastewater environments to recognised international standards.