AirSprayTech Academy Certificate Program

Water and Wastewater Protective Coating Systems

Article 21 of 24

Inspection, Testing, and Quality-Control Documentation

Verifying that the installed coating system meets the specification before the structure returns to service

Inspection Is Part of the Installation

Inspection is not something performed only after the coating work is complete. Effective quality control begins before surface preparation, continues through mixing and application, and ends only after the completed system has been tested, repaired, documented, and accepted.

The purpose of inspection is not to create paperwork or find fault with the crew. It is to identify conditions that could reduce service life while corrective action is still practical. The contractor, inspector, manufacturer, engineer, and facility owner should understand the acceptance criteria before work begins.

Establish the Inspection Plan Before Mobilization

The project specification and approved coating-system documents should define what will be inspected, how measurements will be taken, how frequently testing will occur, who will perform it, and what results constitute acceptance.

A practical inspection plan should identify:

• The coating-system components and required thickness of each coat.
• Specified surface cleanliness, profile, moisture, and substrate condition.
• Environmental limitations and required measurement frequency.
• Wet-film and dry-film thickness requirements.
• Visual acceptance criteria for runs, sags, pinholes, overspray, contamination, and other defects.
• Holiday-detection voltage, equipment, procedures, and acceptance limits.
• Adhesion, cure, hardness, or other testing required by the specification.
• Hold points that require approval before the next operation begins.
• Repair, retesting, documentation, and final-acceptance procedures.

Testing should not be invented after the coating has been installed. Some tests are destructive, and some require test panels, witness areas, embedded instruments, or access that must be planned before application.

Contractor Quality Control and Independent Inspection

Contractor quality control and owner inspection are related, but they are not identical. The contractor remains responsible for controlling the work whether or not an independent inspector is present.

• Quality control is performed by the contractor to keep the work within specification.
• Quality assurance is performed for the owner or responsible authority to verify that the contractor's controls and completed work satisfy the contract.
• Manufacturer observation may provide product-specific technical guidance but does not automatically replace the contractor's responsibility or the owner's inspection program.

Inspection responsibilities, authority, notification requirements, and reporting relationships should be defined in writing. An inspector should not direct unsafe work or make unauthorized changes to the coating system.

Verify Instruments Before Use

A reading is only useful when the instrument is appropriate for the test, functioning correctly, and used by a trained person. Before work begins, confirm the instrument's range, resolution, condition, calibration status, adjustment procedure, and compatibility with the substrate and coating.

• Inspect probes, leads, batteries, cables, connectors, electrodes, and contact surfaces.
• Use certified standards, shims, reference plates, or verification devices required by the test procedure.
• Verify instruments at the required frequency and after suspected damage or abnormal readings.
• Record the instrument manufacturer, model, serial number, calibration status, and verification results.
• Protect instruments from contamination, moisture, impact, excessive heat, and improper storage.

Calibration, verification, and adjustment are not interchangeable terms. Follow the instrument manufacturer and referenced standard for the specific procedure being performed.

Environmental Inspection During Application

Environmental conditions can change rapidly inside tanks, clarifiers, galleries, process buildings, and outdoor structures. Readings taken only at the beginning of a shift may not represent the conditions present during the entire application.

Record, as applicable:

• Air temperature.
• Substrate temperature.
• Relative humidity.
• Calculated or instrument-reported dew-point temperature.
• The difference between substrate temperature and dew point.
• Ventilation status, airflow, weather conditions, and evidence of condensation.

Readings should be taken near the actual work surface and repeated at the frequency required by the specification, whenever conditions change, and before application resumes after an interruption.

Visual Inspection

Visual inspection should be performed after each coat and before the next coat conceals the work. Adequate lighting and access are essential. Inspectors should view the surface from multiple directions because low-angle lighting can reveal defects that are difficult to see under general illumination.

Look for:

• Pinholes, holidays, voids, craters, fisheyes, and porosity.
• Runs, sags, curtains, puddles, and excessive buildup.
• Dry spray, overspray, rough texture, poor flow, or insufficient coverage.
• Blisters, bubbles, swelling, lifting, wrinkling, checking, or cracking.
• Contamination, insects, debris, water marks, or foreign material.
• Incomplete stripe coating at welds, edges, bolts, penetrations, and difficult geometry.
• Missed areas, thin areas, color variation, or incomplete hiding.
• Poorly formed terminations, transitions, coves, seams, and repair boundaries.

Mark defects using a method that does not damage or contaminate the coating. Solvent markers, wax crayons, and incompatible tapes should not be used unless approved.

Wet-Film Thickness

Wet-film thickness measurements give the applicator immediate information while the coating can still be adjusted. A wet-film gauge is pressed into the freshly applied material, and the reading is interpreted according to the gauge instructions.

The theoretical relationship between wet-film thickness and dry-film thickness depends on the coating's volume solids:

For example, a coating with 80 percent volume solids applied at 20 mils wet would theoretically produce approximately 16 mils dry before considering thinning, surface profile, transfer loss, measurement variation, or other field factors.

Wet-film testing may not be practical for extremely fast-reacting materials, heavily textured coatings, aggregate-filled systems, or surfaces where contact would disturb the film. Follow the product and project requirements.

Dry-Film Thickness on Steel

Nondestructive dry-film thickness gauges are commonly used on coated steel. ASTM D7091 addresses the use of magnetic and eddy-current gauges, while AMPP/SSPC-PA 2 establishes procedures for determining conformance with specified thickness ranges on metal substrates.

The inspector must understand the difference between an individual gauge reading, a spot measurement, and an area measurement. Acceptance is normally based on the sampling plan and permitted ranges established by the specification—not on selecting only the highest or lowest readings.

• Verify the gauge on an uncoated substrate or an approved reference surface.
• Account for the effect of abrasive-blast surface profile.
• Take readings at the specified number and distribution of locations.
• Include difficult geometry, edges, welds, repairs, and suspected thin areas when appropriate.
• Record individual readings and required calculated averages.

Thickness on Concrete Requires a Defined Method

Conventional magnetic dry-film gauges do not measure coating thickness directly on concrete. Thickness may instead be controlled through wet-film measurements, material consumption, depth gauges, test panels, embedded references, drilled or cut samples, ultrasonic methods approved for the system, or other specified procedures.

Concrete texture, porosity, bugholes, repairs, high spots, and profile variation make thickness interpretation more difficult. The measurement method and acceptance criteria must be agreed upon before application.

Material Consumption as a Quality-Control Tool

Material usage should be compared with the coated area and the manufacturer's theoretical coverage. This comparison cannot replace direct thickness measurements, but it can reveal a significant discrepancy that deserves investigation.

The calculation should consider:

• Actual surface area, including structural details and difficult geometry.
• Specified thickness and product volume solids.
• Surface profile and concrete porosity.
• Material remaining in containers, hoses, pumps, filters, and mixing equipment.
• Overspray, waste, spillage, test spraying, and discarded mixed material.
• Material used for stripe coats, repairs, and reinforcement.

Unexpectedly low consumption may indicate insufficient thickness or missed areas. Unexpectedly high consumption may indicate excessive buildup, inaccurate area calculations, abnormal waste, or poor transfer efficiency.

Holiday Detection on Conductive Substrates

Holiday detection locates discontinuities in a nonconductive coating applied over an electrically conductive substrate. ASTM D5162 provides procedures for discontinuity testing on metallic substrates. Depending on coating thickness and system requirements, testing may use low-voltage wet-sponge equipment or high-voltage spark testing.

• Confirm that the coating has cured sufficiently for testing.
• Verify that the coating and substrate are suitable for the selected method.
• Use the voltage or test settings required by the specification and coating manufacturer.
• Establish a reliable electrical ground or return connection.
• Verify instrument operation before, during, and after testing.
• Move the electrode at a controlled rate while maintaining proper contact.
• Mark each discontinuity without damaging or contaminating the lining.
• Repair and retest every identified holiday.

Excessive Test Voltage Can Damage the Coating

A high-voltage holiday detector is not simply turned up until a spark appears. Excessive voltage can puncture or carbonize an otherwise sound coating, create new defects, damage thin films, and expose personnel to unnecessary electrical hazards.

Test voltage must be established from the approved standard, actual coating thickness, manufacturer instructions, and project specification. Operators must be trained in the equipment and the hazards of its use.

Holiday Detection on Concrete

Holiday testing over concrete can be more difficult because concrete conductivity varies with moisture content, density, thickness, temperature, and contact with ground or reinforcing steel. Dry concrete may not provide a reliable electrical return path.

Some projects use conductive primers, conductive underlayers, grounded metal mesh, or other manufacturer-approved systems to make electrical discontinuity testing possible. These components must be included in the original system design; they should not be improvised after application.

Before testing the entire structure, confirm that the proposed method can reliably detect a known discontinuity in a representative area without damaging the lining.

Adhesion Testing

Pull-off adhesion testing applies a perpendicular tensile force through a bonded loading fixture. ASTM D4541 addresses pull-off testing of coatings on metal substrates. ASTM D7234 addresses pull-off strength of coatings on concrete.

Adhesion testing is normally destructive. Test locations, frequency, loading-fixture size, adhesive, cutting procedure, cure time, test equipment, loading rate, acceptance value, and repair method should be specified before testing begins.

Record both the measured value and the failure location:

• Adhesive failure between the coating and substrate.
• Adhesive failure between individual coating layers.
• Cohesive failure within a coating layer.
• Cohesive failure within the concrete substrate or repair material.
• Glue failure between the test fixture and coating.

A numerical value without the failure mode can be misleading. Concrete may fail internally before the bond between the coating and concrete is fully challenged.

Cure and Hardness Verification

A coating may appear dry at the surface before it has developed the cure required for immersion, chemical exposure, disinfection, mechanical service, adhesion testing, or holiday detection.

Cure may be evaluated using one or more approved methods:

• Elapsed time at documented air and substrate temperatures.
• Manufacturer-approved hardness testing.
• Solvent-rub or chemical-resistance testing when appropriate for the chemistry.
• Shore hardness testing for elastomeric or thick-film systems.
• Test coupons or retained cure samples produced during application.
• Product-specific analytical testing when required.

The test method must be appropriate for the coating chemistry. A field method used for one epoxy, polyurethane, polyurea, or vinyl ester system should not automatically be applied to another product.

Repair and Retesting

Defects must be evaluated before repair. The repair procedure should address the cause—not merely cover the visible symptom.

1. Define and mark the complete defective area.
2. Determine whether the problem is isolated or evidence of a broader condition.
3. Remove unsound, contaminated, uncured, or poorly bonded material.
4. Feather, abrade, clean, and prepare the repair boundary as required.
5. Apply compatible repair materials within the permitted recoat conditions.
6. Allow the repair to cure for the specified period.
7. Repeat the visual, thickness, holiday, adhesion, cure, or other test that identified the defect.
8. Document the location, cause, procedure, materials, personnel, and retest results.

Repairs should be blended into the surrounding coating without creating abrupt edges, unsealed seams, entrapped contamination, or unverified overlap.

Safety During Inspection and Testing

Inspection inside tanks, wet wells, digesters, vessels, pipelines, and enclosed treatment structures may involve permit-required confined-space hazards. Coating cure does not eliminate atmospheric, engulfment, electrical, access, or process hazards.

Inspectors and testing personnel must be included in the entry permit, atmospheric monitoring, ventilation, communication, lockout, fall-protection, rescue, and personal-protective-equipment plans. Holiday detectors and other electrical instruments must be evaluated for safe use in the work environment.

Required Quality-Control Documentation

The final project record should allow another qualified person to understand what was installed, where it was installed, and how compliance was verified. Records may include:

• Approved product data sheets, safety data sheets, submittals, and specification sections.
• Material-delivery records, lot numbers, batch numbers, quantities, and shelf-life verification.
• Surface-preparation and substrate-condition reports.
• Environmental readings and ventilation records.
• Mixing, thinning, induction, pot-life, and plural-component ratio records.
• Daily production areas, crew assignments, and application times.
• Wet-film and dry-film thickness readings.
• Holiday-detection settings, locations, results, repairs, and retests.
• Adhesion, hardness, cure, and other test results.
• Nonconformance reports, written dispositions, and corrective actions.
• Photographs linked to identifiable locations and dates.
• Final punch-list completion and written acceptance.

Contractor's Field Standard

Inspect each stage before the next stage hides it. Use the correct instrument, follow the specified procedure, record the actual results, correct deficiencies, and retest repairs. A coating system is not complete merely because the final coat has been applied—it is complete when the installed system has been verified and accepted.

Knowledge Check

1. Why should inspection requirements be established before coating work begins?
2. What is the difference between contractor quality control and owner quality assurance?
3. Why are wet-film measurements valuable to the applicator?
4. Why can conventional magnetic dry-film gauges not be used directly on concrete?
5. Why must holiday-test voltage be based on the approved procedure and coating thickness?
6. Why must a pull-off adhesion report include the location and type of failure?
7. What information should be recorded when a coating defect is repaired?

Technical References

• AMPP/SSPC-PA 2-2022: Procedure for Determining Conformance to Dry Coating Thickness Requirements.
• ASTM D7091: Standard Practice for Nondestructive Measurement of Dry Film Thickness of Nonmagnetic Coatings Applied to Ferrous Metals and Nonmagnetic, Nonconductive Coatings Applied to Non-Ferrous Metals.
• ASTM D4414: Standard Practice for Measurement of Wet Film Thickness by Notch Gages.
• ASTM D5162-24: Standard Practice for Discontinuity Testing of Nonconductive Protective Coating on Metallic Substrates.
• ASTM D4541-22: Standard Test Method for Pull-Off Strength of Coatings Using Portable Adhesion Testers on metal substrates.
• ASTM D7234-22: Standard Test Method for Pull-Off Strength of Coatings on Concrete Using Portable Pull-Off Adhesion Testers.
• ASTM D3276: Standard Guide for Painting Inspectors on metal substrates.
• ASTM D6132: Standard Test Method for Nondestructive Measurement of Dry Film Thickness of Applied Organic Coatings Using an Ultrasonic Coating Thickness Gage.
• OSHA 29 CFR 1910.146: Permit-Required Confined Spaces.
• Manufacturer requirements: Current product data sheets, application instructions, inspection procedures, cure requirements, and equipment manuals for the installed system.

Standards may be revised, withdrawn, or replaced. Confirm the current edition required by the contract and obtain the complete standard before developing project procedures. A standard's title or summary is not a substitute for its full requirements.

Professional responsibility: Inspection results must be reported accurately and without selective omission. Do not change acceptance limits, testing frequency, instrument settings, or repair requirements without written authorization from the responsible project authority.

Copyright © 2026 Azimuth Spray Systems, LLC. All Rights Reserved.

No part of this material may be reproduced, copied, distributed, republished, transmitted, stored, or used in any form or by any means without prior written permission from Azimuth Spray Systems, LLC, except for brief quotations used with proper attribution.

AirSprayTech.com - The Finishing Authority®