In wastewater infrastructure rehabilitation, improper installation will cause even the most advanced coating system to fail prematurely. Quality assurance and quality control form the foundation of long-term performance, yet crews often treat them as an afterthought.
Industry experience shows that surface preparation and QA/QC account for roughly 90% of an installed coating system’s success — and 90% of failures when they are not done correctly.
In municipal rehab projects, coating systems act as structural reinforcement corrosion barriers and, in high-infiltration areas, seals that keep groundwater out. To achieve that performance, utilities and contractors need a clear QA/QC road map that covers preparation, application and post-cure inspection.
The Case for QA/QC
Skipping QA/QC steps costs municipalities money and shortens asset life. One common scenario involves patching a structure, stopping infiltration and then leaving it unprotected. Without a bonded, chemical-resistant coating, the repaired substrate begins to deteriorate again. In some cases, the asset needs another round of cleaning, patching and sealing within a decade.
The coating protects all the work underneath. In wastewater environments, it acts as a barrier that ensures repairs last.
Stage 1: Pre-Installation QA
Before applying any coating, crews need to evaluate the substrate and prepare it according to recognized industry standards. At this stage, QA focuses on identifying problems, defining goals and establishing baselines.
1. Follow industry standards
Project specifications should reference guidelines from organizations such as ASTM, AMPP and ICRI. These resources define the minimum acceptable methods, means and conditions for QA/QC, surface preparation, coating application and inspection testing. All QA/QC requirements should be detailed in the specification, including who will perform the test, where and how it will be conducted, and how it will be recorded/reported.
2. Prepare the surface
Bond strength depends on a clean surface with the right profile. The International Concrete Repair Institute provides surface profile comparators. Wastewater specifications often call for CSP 3 to CSP 5 for cementitious substrates. Crews should remove all contamination, laitance and loose material by pressure washing, abrasive blasting or other mechanical methods.
3. Stop leaks
Technicians must eliminate active leaks before coating installation. They can inject hydrophobic or hydrophilic grouts into cracks or joints to seal water entry points. Hydraulic cement can stop small weeps, but injection grouts usually last longer in high-infiltration areas.
4. Check pH
Concrete surfaces should be neutral at a minimum before coating. Acidic residues from cleaning or ongoing corrosion can reduce adhesion if they remain.
Stage 2: QA/QC During Installation
During installation, QC verifies that the work meets the specification and that the coating will perform in service.
1. Handle materials correctly
Crews must store and mix coating materials according to the manufacturer’s requirements. They should document batch numbers and mixing times.
2. Apply coating properly
Trained applicators produce the best results. High-build epoxy linings, for example, require even, consistent passes to achieve uniform thickness without pinholes.
3. Measure thickness
Installers or Inspectors should measure wet film thickness according to ASTM D4414 during application by Notched Gages. Measurements shall be taken and documented for submission to the owner. Then, after the coating has cured, dry film thickness testing can be done using calibrated gauges. This confirms the coating meets the minimum thickness needed for chemical resistance and, in structural linings, for added mechanical strength.
4. Monitor environmental conditions
QA pros should log ambient and substrate temperatures, humidity and dew point throughout the application. These factors affect curing and adhesion.
Stage 3: Post-Installation QA/QC
After curing, post-installation checks confirm that the system will perform under actual service conditions.
1. Perform holiday testing
Concrete wastewater structures can release moisture vapor or air during curing, which may create pinholes in the coating. Holiday testing detects these flaws so crews can repair them before the structure returns to service.
2. Test adhesion
Pull-off adhesion tests measure the force required to detach the coating from the substrate and identify the mode of failure. This process verifies that the bond meets specified minimum requirements. A well-bonded coating reinforces a structure and prevents groundwater from seeping behind it and displacing it under hydrostatic pressure.
3. Document everything
QA/QC files should include surface preparation photos, pH readings, profile measurements, WFT & DFT logs, environmental records, holiday test results and adhesion test data. This record proves compliance and provides a baseline for future inspections.
Techniques That Support QA/QC Success
Use composite systems
When a structure needs both physical rebuilding and chemical protection, crews can combine cementitious repairs with a polymeric coating. The cement restores structural integrity and shape, while the coating seals against corrosion and infiltration.
Match thickness to conditions
In high-hydrostatic-pressure situations, engineers can calculate coating thickness based on depth, diameter and material strength to ensure it can resist external loads. Many wastewater linings are applied at 125 mils or more to provide both protection and structural reinforcement.
Train crews and certify skills
Industry and manufacturer trained coating technicians and inspectors understand the aggressive conditions these systems face and how to apply coatings that withstand them. A trained crew reduces rework and extends service life.
The Cost of Skipping Steps
Premature coating failure almost always results from preventable mistakes.
- Verification that the proper coating system has been specified for use within the intended service environment.
- Delamination usually comes from poor surface preparation or from coating overactive leaks.
- Blistering often results from infiltrating or trapped moisture or gases in the substrate, which proper moisture measurement and environmental monitoring can prevent. Also, the use of surface penetrating primers can assist in lessening blisters and pinholes due to off-gassing.
- Pinhole corrosion starts at small discontinuities that holiday testing could have identified.
Skipping QA/QC on a coating project removes all means of verification that the job is done right. Although it might save a little time and money up front, this can be a very expensive mistake down the road. Rework costs will be far more than following the correct QA/QC process the first time.
The Supplier’s Role
Coating suppliers should actively support QA/QC efforts. This includes reviewing specifications, providing technical service during surface preparation and application, training applicators and assisting with inspections. When suppliers act as technical partners instead of just material providers, the odds of long-term success increase.
Act Now: Prioritize QA/QC
In wastewater rehabilitation, QA/QC ensures that the project delivers on its objectives. When utilities and contractors make QA/QC an integral part of their work, they reduce the risk of premature failure, protect investments in structural repairs and extend asset service life.
From well-written specifications, proper coating recommendations, leak elimination and surface profiling, coating system installation to adhesion testing and documentation, every step plays a crucial role in achieving long-term performance.
Matt Wierzchowski is an account manager with PPG’s Protective and Marine Coatings business, focusing on water and wastewater infrastructure.
