Holiday Testing of High Performance Coatings,

SP0188-2006 Standard and Best Practices:

Executive Summary

This white paper examines the NACE SP0188-2006 standard for holiday testing of protective coatings on steel and concrete substrates, with specific focus on water and wastewater tank applications. It provides a comprehensive analysis of high and low voltage holiday detection methods, their differences, and appropriate applications. Additionally, it explores how epoxy surfacers can significantly reduce holiday occurrence, thereby enhancing coating system performance and extending service life of critical water infrastructure.

1. Introduction to SP0188-2006

The NACE SP0188-2006 standard, "Discontinuity (Holiday) Testing of New Protective Coatings on Conductive Substrates," establishes the industry guidelines for detecting coating discontinuities (holidays) in protective coating systems. Originally published by NACE International (now AMPP - Association for Materials Protection and Performance), this standard provides critical methodology for ensuring coating integrity in various industrial applications.

For water and wastewater infrastructure, where coating failures can lead to contamination, structural degradation, and costly repairs, proper holiday detection is particularly crucial. The SP0188-2006 standard offers a systematic approach to identifying pinhole defects, thin spots, and other discontinuities that might not be visible to the naked eye but could compromise coating performance.

The standard covers:

• Inspection procedures for newly applied coatings
• Equipment specifications and calibration requirements
• Testing parameters based on coating thickness and substrate type
• Documentation and reporting requirements
• Safety considerations

When properly implemented, these procedures help ensure that water and wastewater containment structures maintain their structural integrity, meet regulatory requirements, and achieve their expected service life.

2. Overview of Holiday Testing

Holiday testing (also known as discontinuity testing or porosity testing) is a non-destructive evaluation method used to identify defects in protective coating systems that might otherwise go undetected through visual inspection alone. These defects, called holidays, include:

• Pinholes
• Thin spots
• Cracks
• Misses
• Contamination inclusions
• Mechanical damage

In water and wastewater applications, where coating systems protect both steel and concrete substrates from aggressive chemical environments, holiday detection is essential. Even microscopic breaches in the coating can allow water penetration, leading to:

• Corrosion of steel substrates
• Chemical attack of concrete
• Microbial influenced corrosion
• Structural deterioration
• Contamination risks
• Premature coating failure

Holiday testing should be performed after the coating has sufficiently cured according to manufacturer specifications but before the structure is placed into service. This timing allows for remediation of any identified defects before the system faces operational stresses.

There are two primary methodologies for holiday detection:

1. Low Voltage Testing (Wet Sponge Method) - Generally used for coatings less than 20 mils (500 μm) thick
2. High Voltage Testing (Spark Testing Method) - Used for coatings greater than 20 mils (500 μm) thick

Each method has distinct applications, advantages, and limitations particularly relevant to water and wastewater infrastructure, which we will explore in detail in subsequent sections.

3. High Voltage Holiday Testing

Principles and Methodology

High voltage holiday testing, also known as spark testing or jeeping, operates on the principle of electrical conductivity differences between the coating system and the substrate. The method applies a high voltage (typically DC) to a conductive brush, probe, or electrode that is moved across the coated surface. When the electrode passes over a holiday, the electrical circuit is completed through the substrate, triggering an audible alarm, visible spark, or both.

The SP0188-2006 standard establishes specific voltage requirements based on coating thickness:

• For coatings between 20-50 mils (500-1,270 μm): 100-150 volts per mil
• For coatings thicker than 50 mils (1,270 μm): 80-100 volts per mil

For water and wastewater tanks, where coating systems on concrete substrates may exceed 60-125 mils in thickness, proper voltage selection is critical for effective holiday detection without damaging the coating.

Equipment and Techniques

High voltage holiday detection equipment typically consists of:

1. Power Source - Usually battery-powered DC voltage
2. Control Unit - Allows adjustment of voltage output
3. Detector Wand - Conductive brush, sponge, or spring electrode
4. Ground Wire - Connects to substrate to complete the circuit
5. Signal Device - Visual and/or audible alarm indicators

For water and wastewater tank applications:

• Steel Tanks: The ground wire connects directly to the tank structure
• Concrete Tanks: Grounding requires embedded conducting elements or saturating the concrete to provide conductivity

Testing techniques vary based on tank configuration:

• For flat surfaces: Straight-line sweeping motions with 3-6 inch wide electrodes
• For corners and edges: Specialized narrow brushes or spring electrodes
• For complex geometries: Custom-shaped electrodes may be required

The speed of inspection should be maintained at approximately 1 ft/second (30 cm/second) to ensure thorough coverage without compromising detection sensitivity.

Applications and Standards

For water and wastewater tanks, high voltage testing is particularly applicable for:

• Thick film epoxy linings (>20 mils)
• Polyurethane and polyurea coatings
• Multi-layer systems with aggregate reinforcement
• Glass flake-reinforced linings
• Plural-component spray-applied systems

The SP0188-2006 standard provides specific guidance for water infrastructure:

• Potable Water Applications: Compliance with NSF/ANSI 61 is required alongside holiday testing to ensure both structural integrity and water quality protection
• Wastewater Applications: Higher detection voltage may be required due to thicker coating systems designed to resist chemical attack

The standard recommends that test voltages for concrete substrates may need to be increased by 20-40% compared to steel substrates due to the semi-conductive nature of concrete, particularly when testing thick film linings in wastewater applications.

4. Low Voltage Holiday Testing

Principles and Methodology

Low voltage holiday testing, commonly known as the wet sponge method, employs a significantly lower voltage (typically 67.5 or 90 volts DC) compared to high voltage testing. The method uses moisture as a conductor to complete an electrical circuit when the testing apparatus encounters a coating discontinuity.

According to SP0188-2006, low voltage testing is generally limited to coating systems less than 20 mils (500 μm) in thickness. The method works on the principle that when a moistened sponge passes over a holiday, the water creates a conductive path through the defect to the substrate, completing the circuit and triggering an alarm.

For water and wastewater applications, low voltage testing is most relevant for:

• Thin film primer systems
• Single-coat thin film epoxies
• Intermediate coats before topcoat application
• Repair areas with thin film applications

Equipment and Techniques

Low voltage holiday detection equipment typically consists of:

1. Power Supply - Usually battery-powered (9V or similar) DC voltage source
2. Control Unit - Contains the electrical circuit and indicator systems
3. Wet Sponge Electrode - Typically a cellulose sponge saturated with wetting solution
4. Ground Connection - Wire connecting to the substrate
5. Signal Device - Audible buzzer and/or visual indicator

For water and wastewater tank applications:

• Wetting Solution: Generally water with a wetting agent (0.1-0.2% non-ionic surfactant) to reduce surface tension and improve conductivity
• Sponge Moisture Level: Should be damp but not dripping to prevent false positives
• Ground Connection: Must maintain consistent contact with the substrate

Testing techniques for tank surfaces include:

• Systematic overlapping patterns to ensure complete coverage
• Special attention to edges, corners, and geometric transitions
• Slower inspection speed (approximately 20 ft²/minute) than high voltage testing
• Regular rewetting of the sponge to maintain proper conductivity

Applications and Standards

For water and wastewater tanks, low voltage testing is particularly suitable for:

• Thin film primers (<5 mils)
• Intermediate coats in multi-coat systems
• Single coat systems under 20 mils
• Areas adjacent to equipment or instrumentation sensitive to high voltage
• Steel tank linings with thin film specifications

The SP0188-2006 standard provides specific guidance for low voltage testing in water infrastructure:

• Equipment must be verified daily using test plates with artificial holidays
• Wetting solution should not contain chemicals that might contaminate potable water systems
• Documentation should include holiday locations, testing parameters, and environmental conditions
• Testing should proceed only when surface temperature is at least 5°F above the dew point

For concrete substrates in water/wastewater applications, low voltage testing has limitations due to:

• Concrete's natural porosity and moisture content
• Varying electrical conductivity of concrete
• Difficulty in establishing consistent grounding

In these cases, the standard recommends considering alternative testing methods or modifications to standard procedures.

5. Comparative Analysis: High vs. Low Voltage Holiday Testing

Key Differences

Selection Criteria for Water/Wastewater Tank Applications

The choice between high and low voltage testing for water and wastewater tanks depends on several factors:

1. Coating System Characteristics:

• Tank Lining Thickness: Dictates the primary selection criterion (>20 mils = high voltage)
• Coating Type: Some coatings (like certain polyurethanes) may be more susceptible to damage from high voltage
• Application Method: Spray-applied systems often require different testing protocols than trowel-applied systems

2. Substrate Considerations:

• Steel Tanks: Both methods are effective with proper grounding
• Concrete Tanks: High voltage typically more effective, but requires specialized grounding approaches
• Hybrid Structures: May require both methods in different areas

3. Environmental Factors:

• Ambient Humidity: Can affect low voltage test reliability
• Surface Moisture: May require extended drying periods before testing
• Temperature Gradients: Can affect both test methods differently

4. Application-Specific Requirements:

• Potable Water Storage: May favor less invasive low voltage testing where applicable
• Wastewater Treatment: Often requires high voltage due to thicker, chemical-resistant linings
• Municipal Water Systems: May have specific regulatory requirements governing testing methods

According to SP0188-2006, the final selection should be made based on the coating manufacturer's recommendations, project specifications, and the specific protection requirements of the water/wastewater system.

6. Role of Epoxy Surfacers in Holiday Reduction

Epoxy surfacers play a crucial role in minimizing holiday occurrence in protective coating systems for water and wastewater tanks, particularly on concrete substrates. These specialized materials are applied before the primary coating system to address inherent substrate irregularities that frequently lead to holidays.

How Epoxy Surfacers Reduce Holidays

1. Surface Profile Improvement

Concrete substrates often present numerous challenges that contribute to holiday formation:

• Bug holes and air voids
• Honeycombing
• Cold joints
• Form tie holes
• Surface laitance
• Aggregate exposure

Epoxy surfacers effectively:

• Fill surface irregularities, creating a more uniform substrate
• Reduce sharp peaks and valleys that can cause coating thin spots
• Address porosity issues that might otherwise lead to outgassing and pinholes
• Create a smoother transition at joints, corners, and penetrations

2. Enhanced Coating Application

By providing an improved substrate, epoxy surfacers allow for more consistent application of subsequent coating layers:

• More uniform coating thickness
• Reduced tendency for sags and runs
• Better flow and leveling characteristics
• Fewer application-related defects

3. Reduced Substrate-Related Holiday Mechanisms

Epoxy surfacers address several concrete-specific mechanisms that cause holidays:

• Outgassing Mitigation: By sealing concrete porosity, surfacers significantly reduce air and moisture vapor release during coating cure that often causes pinholes
• Alkalinity Buffering: Creates a barrier between high-pH concrete and pH-sensitive coatings that might otherwise develop holidays due to chemical incompatibility
• Moisture Control: Helps regulate moisture movement through concrete that can disrupt coating adhesion and integrity

Application Considerations for Water/Wastewater Tanks

For optimal holiday reduction in water and wastewater applications:

1. Selection Criteria:

• Chemical Compatibility: Must be compatible with both the substrate and subsequent coating layers
• Water Resistance: Should provide excellent resistance to constant immersion
• Viscosity Properties: Should match the substrate condition (lower viscosity for hairline cracks, higher viscosity/thixotropy for larger voids)
• Moisture Tolerance: Many water/wastewater structures have inherent moisture issues requiring moisture-tolerant surfacers

2. Application Methods:

• Steel Substrates: Typically applied by trowel or spray to address pitting and irregularities
• Concrete Substrates: Applied by trowel, squeegee, or specialized spray equipment depending on formulation

3. Thickness Considerations:

• Thin Film Surfacers: 10-20 mils for minor irregularities
• High-Build Surfacers: 40-125+ mils for significant surface defects
• Aggregate-Extended Systems: Up to 1/4 inch for severe cases of surface deterioration

Holiday Testing After Surfacer Application

SP0188-2006 provides guidance for holiday testing of surfacer layers:

• The surfacer should be tested as an independent layer before primary coating application
• Testing method should match the surfacer thickness (low voltage for thin applications, high voltage for thicker applications)
• Grounding considerations may differ from those of the final coating system
• Repair procedures should be performed before proceeding with the primary coating application

By incorporating properly selected and applied epoxy surfacers into water and wastewater tank coating specifications, holiday incidence can be reduced by 60-85% according to industry case studies, resulting in more reliable protection systems and extended service life.

7. Industry Best Practices for Holiday Testing in Water/Wastewater Applications

Successful holiday detection for water and wastewater tank coatings requires adherence to established best practices aligned with SP0188-2006 while addressing industry-specific challenges.

Pre-Testing Preparations

1. Environmental Conditions:

• Verify temperature is within specified range (typically 50-100°F)
• Confirm relative humidity is below maximum threshold (generally <85%)
• Ensure surface temperature is at least 5°F above dew point
• Document environmental conditions for quality assurance records

2. Coating Readiness:

• Allow complete cure according to manufacturer's specifications
• Verify coating thickness using non-destructive methods
• Ensure surface is clean and free of contamination
• Confirm absence of condensation or surface moisture

3. Equipment Verification:

• Calibrate equipment daily using verification test plates
• Check battery condition and charging status
• Verify proper grounding and electrical continuity
• Ensure electrode/sponge condition is appropriate for the application

Testing Execution

1. Systematic Inspection Approach:

• Divide large tanks into manageable sections (typically 10'×10')
• Use reference points to track inspection progress
• Maintain consistent electrode pressure and speed
• Ensure overlap between inspection passes

2. Documentation Requirements:

• Mark all identified holidays for repair
• Record holiday locations on inspection maps
• Document testing parameters (voltage, equipment type)
• Photograph representative holidays for quality records

3. Special Considerations for Water/Wastewater Tanks:

• Submerged Zones: Require 100% inspection coverage
• Splash Zones: May require higher detection voltages due to exposure severity
• Vapor Zones: Particular attention to overhead surfaces
• External Tank Surfaces: Modified testing approach based on exposure conditions

Post-Testing Procedures

1. Holiday Marking and Measurement:

• Circle each holiday with high-visibility marker
• Measure and record holiday density (holidays per 100 ft²)
• Classify holiday types (pinholes, thin spots, inclusions)
• Determine if holiday density exceeds acceptance criteria

2. Repair Methodology:

• Follow coating manufacturer's repair procedures
• Ensure proper surface preparation of defect areas
• Apply repair materials at specified thickness
• Allow proper cure time before re-testing

3. Re-testing Requirements:

• Re-test all repaired areas using the same testing method
• Document secondary holiday detection results
• Verify complete elimination of previously identified holidays
• Prepare final inspection report with certification of results

Acceptance Criteria

SP0188-2006 and industry best practices establish specific acceptance criteria for water and wastewater applications:

• Potable Water Tanks: Zero holidays permitted in immersion areas
• Wastewater Tanks: Maximum 1 holiday per 100 ft² in immersion areas
• Non-Immersion Areas: Maximum 3 holidays per 100 ft²
• Critical Areas (joints, corners, penetrations): Zero holidays permitted

8. Case Studies

Case Study 1: Municipal Potable Water Storage Tank

Project Background:

• 2-million-gallon elevated water storage tank
• Steel substrate with 30-mil high-solids epoxy lining
• 100% high voltage holiday testing required by specification

Challenges:

• Complex geometry at roof-to-wall transitions
• Multiple internal supports and access structures
• Varying environmental conditions during multi-week application

Holiday Testing Approach:

• Used high voltage testing at 3,000 volts (100V per mil)
• Initial testing revealed holiday density of 5.2 per 100 ft²
• Implemented modified application technique at transition areas
• Added epoxy surfacer to weld seams before coating application

Results:

• Reduced holiday density to 0.3 per 100 ft² after process modifications
• Achieved zero holidays after repairs and re-testing
• Five-year inspection showed no coating failures at previous holiday locations
• Extended maintenance interval from 8 to 12 years

Case Study 2: Wastewater Treatment Clarifier

Project Background:

• 120-foot diameter concrete clarifier
• Severely deteriorated concrete requiring extensive repair
• 125-mil high-build epoxy novolac lining system specified

Challenges:

• Extremely porous concrete substrate
• High levels of surface contamination from wastewater exposure
• Multiple areas of concrete spalling and reinforcement exposure

Holiday Testing Approach:

• Applied 60-mil epoxy surfacer to entire concrete surface
• Conducted intermediate holiday testing of surfacer at 5,000 volts
• Applied primary coating system in multiple layers
• Final testing at 9,000 volts per SP0188-2006 guidelines

Results:

• Initial resurfacer testing revealed 32 holidays requiring repair
• Final system testing showed only 5 holidays in 15,000 ft² of surface area
• Post-repair verification confirmed zero holidays
• Ten-year service life achieved in aggressive environment before minor maintenance required

Case Study 3: Dual-Substrate Water Storage Facility

Project Background:

• Combined concrete foundation with steel tank walls
• Different coating systems for each substrate
• Critical transition areas between dissimilar materials

Challenges:

• Different holiday testing requirements for each coating system
• Maintaining continuity across substrate transitions
• Variable environmental conditions affecting testing reliability

Holiday Testing Approach:

• Low voltage (90V) testing for 12-mil steel tank primer
• High voltage (2,500V) testing for 25-mil steel tank topcoat
• High voltage (7,000V) testing for 85-mil concrete foundation coating
• Custom electrode design for transition areas

Results:

• Identified critical holiday concentration at substrate transitions
• Implemented modified detailing procedure with reinforcing fabric
• Re-test confirmed elimination of transition area holidays
• Facility remained in service 15 years with minimal maintenance requirements

9. Conclusion

Holiday testing according to NACE SP0188-2006 represents a critical quality control measure for ensuring the longevity and performance of protective coating systems in water and wastewater tank applications. The fundamental differences between high and low voltage holiday detection methods necessitate careful selection based on coating thickness, substrate type, and service environment.

For water and wastewater infrastructure, where coating failures can have significant economic, environmental, and public health consequences, comprehensive holiday detection provides essential verification of coating system integrity. The appropriate application of high voltage testing for thick film systems and low voltage testing for thin film applications helps ensure that these critical protective barriers perform as designed throughout their intended service life.

The strategic use of epoxy surfacers, particularly on concrete substrates, offers substantial benefits in holiday reduction by addressing inherent substrate irregularities that frequently lead to coating discontinuities. When properly selected and applied, these materials create an optimized surface profile that significantly improves coating application characteristics and reduces holiday formation mechanisms.

By implementing the best practices outlined in this white paper, facility owners, engineers, and contractors can achieve superior coating performance for water and wastewater containment structures, resulting in:

• Extended service life of critical infrastructure
• Reduced maintenance and repair costs
• Improved regulatory compliance
• Enhanced public safety and environmental protection
• Greater return on infrastructure investment

As coating technologies continue to evolve, holiday testing methodologies must adapt accordingly. Ongoing advancements in testing equipment, procedures, and acceptance criteria will further refine the industry's ability to ensure coating integrity and performance for these essential public infrastructure systems.

References

1. NACE SP0188-2006, "Discontinuity (Holiday) Testing of New Protective Coatings on Conductive Substrates"
2. SSPC-PA 9, "Measurement of Dry Coating Thickness on Cementitious Substrates Using Ultrasonic Gages"
3. ACI 515.2R, "Guide to Selecting Protective Treatments for Concrete"
4. AWWA D102, "Coating Steel Water-Storage Tanks"
5. NACE Publication 6H189, "Holiday Detection of Pipeline Coatings"