The Bromley Wastewater Treatment Plant required a long-term protection solution for three silos (two dry, one wet). Existing coatings only covered around 15% of the lower internal surfaces. While the exposed steel was not in direct contact with biosolids, corrosion was increasing and the assets required a durable protective coating system to prevent further degradation.
Our team was mobilised on-site to carry out tank cleaning and apply protective coatings at Bromley Wastewater Treatment Plant.
What We Did
With limited time to prepare, all planning, resourcing and logistics were completed within two weeks. This included transferring staff from another region to meet the scale of the project.
We began with a low-pressure internal wash of all vessels. Once cleaning was completed, we waited for scaffolding to be erected and lifting operations from the silo tops to be finalised. Throughout this stage, we worked closely with engineers and crane operators to maintain a safe and coordinated work environment.
Our Industrial Services team then completed a hard strip, using a 40,000-psi water blasting unit operating at 26 litres per minute – removing most of the existing coating. This was followed by our coatings team delivering a sweep blast with garnet to remove remaining coating and surface corrosion.
Altex Coatings supplied the coating system and specification, which involved a three to four coat system including primer and stripe coats. During application, significant corrosion pitting was identified inside the vessels. This required extra time and care, including back-rolling during application, to ensure full coverage and avoid trapped air in the pitted areas.
Our team worked over a four-week period, completing the protective coatings under a tight 10-day programme.
Meeting complex Challenges
The project presented several challenges, including tight deadlines and overlapping site activities. We worked closely with the Head Contractor to maximise available work windows and maintain progress.
Adverse weather caused a two-day delay, which was accepted by the client as unavoidable. Through strong coordination and flexibility, we were able to deliver the project to the required standard.
Daily site audits conducted by a third-party HSEQ Advisor ensured consistent compliance with safety standards and reinforced our strong site capability throughout the project.
Despite the challenges faced, the project was completed within the required timeframe, with sufficient curing time allowed before silo recommissioning – true demonstration of InterGroup’s ability to mobilise quickly and respond effectively under pressure.
We cleaned and prepared the interior of a wastewater treatment silo for protective coating application
Project Results
The project was delivered on time with minimal issues, reinforcing our ability to meet strict deadlines without compromising quality. This success positioned us as the preferred coating supplier for the Christchurch Wastewater Treatment Plant and strengthened our partnership with the principal contractor, NZ MechTech, paving the way for future collaboration on similar projects.
Client Feedback
The client expressed appreciation for the quality of the finish achieved under a challenging timeframe and noted the professionalism shown in adapting the methodology to meet programme pressures. They also highlighted the proactive communication around substrate pitting and the additional work undertaken to ensure a durable outcome, reinforcing confidence in the coating system and the delivery team.
Internal view of a wastewater treatment silo during surface preparation for protective coating application