Failure of epoxy linings were identified within newly built sewage wet well pumping structures, located on the foreshore of McLeod’s Bay. These structures service both gravity reticulated and pumped raw sewage from the residential catchments of McLeod’s and Urquhart’s Bay on the Whangarei Headlands.

The epoxy linings were originally applied to protect the steel reinforced concrete chambers from inherently corrosive conditions that exist within live sewers. A visual inspection of the coatings indicated early signs of Hydrogen Sulphide (H₂S) attack. If left, the on-set of H₂S within would have corroded and deteriorated the integrity of the steel reinforced concrete structures, drastically reducing the life expectancy of the Council owned asset.

BBR Contech was contracted by United Civil Ltd to reline both structures using Kerneos Aluminates’ Sewpercoat, developed to resist the effects of H₂S corrosion. The product is a blend of calcium aluminate cements (CAC) and CAC aggregates. The product was applied using dry-spray gunite techniques, which was particularly suited to working within this challenging environment.

The benefits of using Sewpercoat for this project were; enabling fast turn-around times working within the live sewer using the products high and early strength gain characteristics and enabling Contech to work with existing damp surface conditions found within both structures. Prior to the application of the new coatings, the existing epoxy linings were removed and the concrete surface of the wet wells were prepared by low volume, high pressure water jetting.