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
