AirSprayTech Academy Certificate Program
Secondary Containment Coating Systems for Industrial Contractors
Article 21 of 24
Common Defects, Failure Analysis, and Repairs
Finding the cause, defining the extent, and making a repair that restores the containment system
Repair the Cause—not Just the Visible Damage
A coating defect is the visible result of something that happened during design, substrate preparation, material storage, mixing, application, curing, service, or maintenance. Covering the visible damage without identifying the cause can trap contamination, moisture, uncured material, or poor adhesion beneath the repair.
A professional repair restores the required continuity, adhesion, thickness, chemical resistance, and physical performance of the containment system. It begins with investigation—not with opening a can of coating.
Learning Objectives
After completing this article, the reader should be able to:
- Recognize common containment-lining defects and their possible causes.
- Distinguish a defect symptom from its root cause.
- Preserve evidence before destructive investigation or repair begins.
- Determine whether a localized repair or broader replacement may be required.
- Develop a written repair procedure with defined acceptance requirements.
- Document and retest completed repairs.
First Protect People and the Facility
Before examining a failed containment area, determine what chemicals were present, whether residues remain, and whether the area has been released for entry. A surface that looks dry may still contain hazardous or reactive material.
Follow the facility’s spill-response, decontamination, confined-space, lockout/tagout, ventilation, respiratory-protection, hot-work, and waste-handling procedures. Obtain the applicable safety data sheets and confirm that sampling, grinding, cutting, heating, or solvent cleaning will not create an additional hazard.
Defect, Damage, and Failure
These terms are often used as though they mean the same thing, but they describe different conditions.
A defect is an imperfection or condition that differs from the specified requirement. A pinhole, thin area, sag, missed termination, or incomplete fabric wet-out may be classified as a defect.
Damage results from an outside event such as impact, dragging equipment, dropped tools, welding, traffic, thermal exposure, or chemical spillage beyond the system’s resistance.
Failure occurs when the system can no longer perform its required function. A lining may fail through loss of adhesion, chemical attack, cracking, permeation, loss of continuity, or deterioration of the underlying substrate.
The Visible Condition Is a Clue
Blistering is not a complete diagnosis. Neither are cracking, peeling, discoloration, pinholes, or softening. Each describes what can be observed. The cause must be determined by examining the system, substrate, installation history, exposure, and failure plane.
Pinholes, Holidays, Voids, and Porosity
Discontinuities can provide a direct path for liquid to reach the substrate. Possible causes include:
- Air or gas escaping from porous concrete.
- Incomplete wetting of a rough or contaminated substrate.
- Air entrained during aggressive mixing.
- Incorrect spray pressure, tip size, atomization, or application technique.
- Material applied below the required thickness.
- Poor wet-out of fiberglass reinforcement.
- Solvent or volatile material escaping from an overly thick coat.
- Failure to stripe-coat corners, welds, edges, penetrations, and other difficult areas.
A repair normally requires cleaning and preparing the discontinuity and enough surrounding sound lining to provide a secure bond. Smearing material over a contaminated pinhole without preparation may conceal the opening without sealing it.
Blistering
Blisters are raised areas produced by pressure or loss of adhesion beneath or within the lining. Possible contributors include:
- Moisture vapor moving through concrete.
- Osmotic pressure caused by soluble contamination.
- Air or gas released from porous concrete during application.
- Application over condensation, moisture, oil, dust, or chemical residue.
- Chemical permeation or absorption.
- Solvent entrapment or application above the permitted thickness.
- Thermal exposure or rapid temperature change.
- Loss of adhesion between layers or at the substrate.
Record blister size, frequency, distribution, location, and relationship to cracks, joints, drains, wet areas, heat sources, spills, and vapor pathways. Opening a representative blister can reveal the failure plane, but this should be done only after the condition has been photographed and a sampling plan established.
Delamination, Peeling, and Loss of Adhesion
Adhesion loss may occur at the substrate, between coating layers, within a weak layer, or within the substrate itself. The failure plane is one of the most important pieces of evidence.
Common causes include:
- Insufficient surface preparation or surface profile.
- Dust, oil, salts, moisture, laitance, corrosion products, or chemical contamination.
- Application outside the recoat window.
- Amine blush or contamination between coats.
- Incompatible materials or an unapproved tie coat.
- Improper mixing ratio or incomplete mixing.
- Application to a weak or deteriorated substrate.
- Chemical, thermal, mechanical, or moisture exposure beyond the system’s capability.
The boundary of a visible delamination may not be the boundary of the actual loss of adhesion. Sounding, probing, adhesion testing, removal of representative sections, or other approved investigation may reveal a substantially larger affected area.
Cracking and Joint-Related Failure
Cracks may occur within the lining or may reflect movement in the underlying substrate. Possible causes include:
- Movement of concrete cracks or construction joints.
- Structural settlement, vibration, loading, or thermal movement.
- A rigid lining bridging an active crack.
- Excessive coating thickness or shrinkage during cure.
- Incorrect mixing ratio or incomplete cure.
- Thermal shock or impact.
- Chemical embrittlement or aging.
A moving joint should not be filled rigidly simply to make it look continuous. The repair must respect the joint’s purpose and anticipated movement. Structural cracks, recurring cracks, or unexplained movement should be evaluated by the responsible engineer before the lining is repaired.
Softness, Tackiness, and Incomplete Cure
A lining that remains soft, tacky, or easily marked may result from:
- Incorrect resin-to-hardener ratio.
- Incomplete mixing or unmixed material from the container walls or bottom.
- Application after usable pot life expired.
- Low substrate or ambient temperature.
- Chemical contamination or incompatible cleaning products.
- Incorrect solvent addition or unauthorized thinning.
- Premature exposure to water, chemicals, cleaning, or traffic.
Uncured thermoset material should not be buried beneath another coat unless the manufacturer provides a specific written corrective procedure. Applying more material does not correct an incorrect mix ratio or incomplete chemical reaction.
Chemical Attack
Chemical attack may appear as:
- Softening, swelling, blistering, or loss of adhesion.
- Cracking, embrittlement, erosion, or loss of thickness.
- Discoloration, staining, loss of gloss, or surface etching.
- Permeation through an apparently intact lining.
- Failure concentrated at seams, repairs, pinholes, penetrations, or thin areas.
Investigation should identify the actual chemical, concentration, temperature, exposure duration, frequency, mixtures, contaminants, cleaning agents, and whether the spill was allowed to evaporate and become more concentrated.
A statement that a lining is “chemical resistant” is incomplete. Resistance depends on the specific exposure and operating conditions. Obtain written guidance from the lining manufacturer before selecting repair materials or returning the area to service.
Rusting and Corrosion Beneath the Lining
Rust staining, underfilm corrosion, lifting at welds, or corrosion spreading from a holiday indicates that the protective barrier has been breached or that the steel was not adequately prepared before application.
Corrosion products occupy more volume than the original steel and can force the lining away from the surface. The repair must extend beyond visibly rusted material to sound, well-adhered lining and properly prepared steel.
Where section loss, pitting, structural damage, or corrosion at welds is found, the owner or responsible engineer should determine whether metal repair or replacement is required before the lining is restored.
Preserve the Evidence
Before scraping, grinding, pressure washing, solvent cleaning, or removing failed material:
- Restrict access and identify the affected area.
- Photograph overall conditions and close-up details with a scale reference.
- Mark locations on a drawing or area map.
- Record the date, environmental conditions, exposure history, and recent operations.
- Collect batch records, daily reports, thickness readings, inspection reports, and repair history.
- Document the size, density, pattern, and boundaries of the condition.
- Identify representative areas for examination and sampling.
- Maintain sample identification and chain-of-custody records when laboratory analysis may be required.
Once the area has been mechanically cleaned, much of the evidence needed to determine the cause may be permanently lost.
A Practical Failure-Analysis Sequence
- Define the problem: Describe what is observed without assigning a cause.
- Establish the extent: Determine whether the condition is isolated, repeated, or widespread.
- Review the history: Examine specifications, product records, application reports, exposure, maintenance, and repairs.
- Examine the failure plane: Identify where separation or deterioration occurred.
- Develop possible causes: Consider design, substrate, materials, workmanship, cure, environment, and service.
- Test the explanations: Use appropriate field observations, measurements, sampling, or laboratory analysis.
- Identify the most supported cause: Base the conclusion on evidence rather than appearance alone.
- Correct the cause: Develop a repair that prevents the same condition from returning.
Determine the Full Repair Boundary
The repair must extend to sound substrate and sound, firmly bonded lining. The visible edge of a blister, crack, stain, or delamination should not automatically be used as the repair boundary.
Methods used to establish the extent may include:
- Visual inspection under adequate lighting.
- Sounding, probing, scraping, or other approved examination.
- Dry-film-thickness or system-thickness measurements.
- Holiday testing where appropriate.
- Pull-off adhesion testing at approved locations.
- Concrete moisture testing or contamination testing.
- Removal of representative sections to examine the substrate and individual layers.
Local Repair or System Replacement?
A localized repair may be appropriate when the cause is understood, the affected area is limited, the surrounding lining is sound, the repair material is compatible, and the repair can restore the specified performance.
Broader removal or replacement may be necessary when adhesion is generally poor, the lining is chemically degraded, moisture pressure is widespread, the system is incompatible with the exposure, the substrate is deteriorated, or numerous repairs would create an unreliable patchwork.
The lowest-cost immediate repair is not always the lowest-cost solution. The decision should consider remaining service life, access, shutdown cost, chemical risk, repair reliability, warranty requirements, and consequences of another release.
The Written Repair Procedure
The repair procedure should be approved before work begins and should identify:
- The defect type, location, cause, and repair boundary.
- Required isolation, decontamination, and safety controls.
- Removal method and required condition of the exposed substrate.
- Surface-preparation standard and required surface profile.
- Preparation of the existing lining and required overlap into sound material.
- Compatible primer, filler, reinforcement, lining, and termination materials.
- Required number of coats and wet- and dry-film thicknesses.
- Environmental limitations, mixing requirements, recoat windows, and cure schedule.
- Inspection hold points and acceptance criteria.
- Required holiday, thickness, adhesion, or cure testing.
- Minimum cure time before cleaning, traffic, immersion, or chemical exposure.
Preparing the Repair Area
Remove failed material until firmly bonded lining and a suitable substrate are reached. Feathering an edge to a thin, weak film can leave an unreliable transition. The perimeter may require a defined cut or termination detail to prevent lifting during removal and preparation.
Existing lining that will receive the repair must be cleaned, decontaminated, roughened, and prepared as required by the manufacturer. Gloss removal alone may not be sufficient when the surface has absorbed chemicals or when the recoat window has been exceeded.
Steel must be prepared to the specified cleanliness and profile. Concrete must be sound, clean, dry to the extent required, and free of weak paste, laitance, curing compounds, contamination, and unsound repair material.
Dust and debris must be removed without introducing oil, moisture, or incompatible residue. The prepared area should be inspected and accepted before repair materials are applied.
Repair Transitions and Overlaps
A successful repair must tie into sound existing lining. The overlap width and preparation method should follow the manufacturer’s written repair instructions. Different layers may require staggered transitions so that all repair edges do not terminate at the same location.
Fiberglass-reinforced systems may require removal and replacement of damaged reinforcement with a specified overlap. The reinforcement must be completely wet out, free of trapped air, and covered to the required thickness.
Repair edges should not create an exposed ledge that can collect liquid or permit chemical entry. Terminations at joints, drains, penetrations, and equipment bases require the same attention as the original installation.
Inspect and Retest Every Repair
A repaired area should be evaluated using the same applicable requirements as the original lining. Depending on the system, this may include visual inspection, thickness measurement, holiday testing, adhesion testing, hardness or cure verification, and examination of transitions.
Mark the repair location on the final drawing and record the materials, batch numbers, installer, application date, environmental conditions, test results, and authorized return-to-service date.
Key Takeaways
- The visible defect is a symptom, not necessarily the cause.
- Protect personnel and confirm decontamination before investigating a failure.
- Preserve photographs, samples, records, and other evidence before cleaning or removal.
- Identify the failure plane and full extent of deterioration.
- Do not bury contamination, uncured material, or poor adhesion beneath a repair.
- Repairs must extend to sound substrate and sound, firmly bonded lining.
- Use a written, manufacturer-approved repair procedure.
- Inspect, test, document, and properly cure every repair before returning it to service.
Technical References
Consult the project specification and current edition of every referenced standard. Standards may be revised after publication of this article.
Professional responsibility:
Coating failure analysis can involve hazardous residues, destructive testing, structural concerns, environmental obligations, and contractual responsibility. Follow the facility’s safety and decontamination procedures, current project requirements, applicable regulations, and the coating manufacturer’s written instructions. Obtain qualified engineering, laboratory, manufacturer, or industrial-hygiene assistance when the cause or safe repair procedure is uncertain.
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