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Water and Wastewater Protective Coating Systems | Article 15 of 24

Selecting Coating and Lining Chemistries for the Exposure

Coating selection should begin with the actual exposure, substrate, application conditions, and service requirements—not with a familiar chemistry, a generic product label, or the lowest material price.

Select a System, Not Merely a Resin Name

“Epoxy,” “polyurethane,” “polyurea,” and “vinyl ester” identify broad chemistry families. Products within the same family can differ substantially in formulation, reinforcement, film thickness, application method, chemical resistance, flexibility, cure, moisture tolerance, and service limitations.

Selection should be based on the complete protective system: substrate repair, resurfacer, primer, intermediate material, lining, stripe coats, reinforcement, joint treatment, termination details, inspection requirements, and cure before service.

“Elastomeric” Is a Performance Description

Elastomeric describes a material’s ability to stretch and recover; it does not identify one specific coating chemistry. Acrylic, polyurethane, polyurea, and other formulated systems may be described as elastomeric.

A specification should identify the actual chemistry, system construction, required properties, thickness, substrate, exposure, and performance criteria rather than relying on the word “elastomeric” alone.

Begin with an Exposure Schedule

The coating contractor, owner, designer, and manufacturer need a common description of what the system must withstand. “Wastewater service” or “water tank” is not enough information.

The exposure schedule should identify:

• Potable water, raw water, process water, wastewater, sludge, or chemical containment
• Continuous immersion, intermittent immersion, splash, headspace, atmospheric, or buried exposure
• Normal and upset chemical concentrations
• Minimum, normal, and maximum temperatures
• Expected pH range
• Hydrogen-sulfide and biogenic sulfuric-acid potential
• Abrasion, erosion, impact, cavitation, and cleaning procedures
• Positive-side and negative-side moisture
• Structural movement, cracking, vibration, and thermal cycling
• UV exposure and weathering
• Required shutdown and return-to-service time
• Regulatory, certification, warranty, and owner requirements

Potable-Water Service

Materials contacting drinking water may need certification to NSF/ANSI/CAN 61 and compliance with applicable AWWA standards, state requirements, owner specifications, and local regulations.

NSF/ANSI/CAN 61 establishes health-effects criteria for materials and products that contact drinking water. Certification does not establish that a product will provide adequate adhesion, corrosion protection, chemical resistance, taste and odor performance, microbial-growth resistance, or service life for a particular project.

Verify the current certification listing for the exact manufacturer, product, formulation, color when applicable, primer, use category, water-contact temperature, tank size or surface-area limitation, cure schedule, and application thickness. Certification of one product does not automatically extend to another product in the same family.

A Chemical-Resistance Chart Is Only a Starting Point

Chemical resistance can change with concentration, temperature, exposure duration, mixtures, contaminants, aeration, pressure, cleaning cycles, and whether exposure is continuous or intermittent.

Obtain written confirmation from the coating manufacturer for the specific service conditions. Do not approve a system solely because a generic chart labels it “recommended” for one chemical at an unspecified concentration or temperature.

Conventional and High-Solids Epoxy Systems

Epoxy systems are widely used on steel and concrete because properly selected formulations can provide strong adhesion, low permeability, chemical resistance, and dependable immersion performance.

Epoxy systems may include:

• Penetrating or surface-tolerant primers
• Conventional-build epoxy coatings
• High-solids and 100-percent-solids epoxies
• High-build reinforced or filled epoxy linings
• Epoxy mortars and resurfacers
• Specialty formulations for potable-water or wastewater service

Potential advantages include strong bond, good barrier performance, broad formulation options, and compatibility with many repair and resurfacing systems.

Limitations can include brittleness, sensitivity to mixing ratio and temperature, amine blush, limited crack movement, chalking under ultraviolet exposure, and restricted chemical or temperature resistance depending on formulation.

Novolac Epoxy Systems

Epoxy novolac formulations generally provide greater chemical and heat resistance than many conventional bisphenol-A epoxy systems. They may be considered for severe chemical exposures, concentrated cleaning chemicals, process areas, and certain wastewater conditions.

“Novolac” does not mean universal chemical resistance. Performance still depends on the exact formulation, film thickness, cure, substrate preparation, chemical concentration, exposure temperature, and service duration.

Some novolac systems can be comparatively rigid and demanding to apply. Confirm their tolerance for substrate movement, dampness, thermal cycling, and the available cure conditions.

Polyurethane Systems

Polyurethane formulations can provide abrasion resistance, flexibility, impact resistance, color and gloss retention, and weathering performance. They may be used as linings, membranes, intermediate layers, or exterior finish coats depending on formulation.

Aromatic and aliphatic polyurethane products can perform differently. An aromatic material may be suitable for protected or immersion service but discolor or chalk under ultraviolet exposure. An aliphatic polyurethane may be selected where exterior color and gloss retention matter.

Some polyurethane components are moisture sensitive during application and cure. Certain products may contain isocyanates and require strict ventilation, respiratory protection, skin protection, training, and exposure control.

Polyurea and Hybrid Systems

Plural-component polyurea systems can provide rapid cure, high film build, toughness, flexibility, and short return-to-service times. Hybrid polyurethane-polyurea products may be formulated to balance reaction speed, application characteristics, and performance.

Rapid reaction can be an advantage, but it leaves little tolerance for incorrect temperature, pressure, ratio, mixing, gun setup, or spray technique. Off-ratio material can appear solid while lacking the intended properties.

Polyurea does not eliminate the need for surface preparation, substrate repair, primer, environmental control, thickness verification, termination detailing, and holiday testing. Confirm the exact formulation’s chemical, immersion, adhesion, and potable-water qualifications.

Vinyl-Ester Systems

Vinyl-ester linings can provide strong resistance to certain acids, solvents, oxidizing chemicals, and elevated-temperature exposures. Reinforced versions may be used in severe chemical environments.

These systems can be sensitive to catalyst ratio, mixing, substrate temperature, humidity, ventilation, film thickness, and cure. Some formulations involve flammable or hazardous volatile components and require careful ignition control and respiratory protection.

Confirm compatibility with the substrate, repair material, primer, exposure, and proposed application method. A vinyl-ester system selected for one acid exposure may not be appropriate for another chemical or for potable-water service.

Acrylic and Other Water-Based Polymer Systems

Acrylic and other water-based polymer coatings can offer lower odor, easier handling, vapor permeability, UV stability, and convenient application. Certain products are useful for atmospheric concrete or steel, exterior surfaces, and less severe service zones.

Many acrylic systems are not intended for continuous immersion, severe chemical exposure, or aggressive wastewater headspaces. Confirm immersion approval, chemical resistance, film thickness, cure conditions, and early-water resistance before selection.

Cementitious and Mineral-Based Systems

Cementitious materials may be used to repair, resurface, waterproof, or protect concrete. Specialty calcium-aluminate, geopolymer, and other mineral-based formulations may be selected for wastewater environments or as substrates beneath polymer linings.

These materials differ significantly in chemical resistance, permeability, curing, thickness, reinforcement, bond, and suitability for direct exposure. A cementitious resurfacer beneath a polymer lining performs a different function from a cementitious material intended as the final exposed surface.

Confirm whether the material is the complete protective system, part of a composite system, or only a substrate-repair component.

Reinforced Lining Systems

Fiberglass fabric, chopped strand, flake reinforcement, scrim, or other reinforcement may be incorporated into certain lining systems to improve crack bridging, thickness control, impact performance, or chemical resistance.

Reinforcement can also introduce laps, wrinkles, trapped air, resin-starved areas, protruding fibers, and difficult terminations when improperly installed.

The specification should define reinforcement type, overlap, saturation, placement, number of layers, termination, intermediate inspection, and repair procedure.

Thin-Film Coating or High-Build Lining?

Film thickness should be based on service requirements and tested system construction. Thin-film systems may be appropriate for atmospheric or moderate exposure. Severe immersion, abrasive flow, chemically aggressive wastewater, and biogenic-acid headspace may require substantially thicker lining systems.

Thickness alone does not establish performance. A thick but porous, off-ratio, poorly bonded, incompletely cured, or holiday-filled lining can fail rapidly.

Specify each coat, wet-film or dry-film requirements as applicable, total system thickness, maximum thickness per pass, reinforcement, stripe coats, and inspection method.

Crack Movement and Flexibility

A lining may bridge a small static crack but fail across an active joint or moving crack. Tensile elongation reported on a free film does not prove that an installed system will tolerate movement while bonded to concrete.

Evaluate crack width, direction, depth, cause, expected movement, temperature change, hydrostatic pressure, and structural significance. Active joints normally require an engineered joint detail rather than continuous application of a rigid lining.

Obtain written movement capability and detail requirements from the system manufacturer and responsible design professional.

Laboratory Data Must Be Interpreted Carefully

Laboratory testing can compare products and document performance under defined conditions. It does not reproduce every combination of substrate condition, application error, chemical mixture, microbial activity, thermal cycle, abrasion, and field exposure.

Review the test method, specimen construction, cure, film thickness, test concentration, temperature, duration, acceptance criterion, and whether the reported property applies to the complete proposed system.

Application Conditions Can Eliminate Otherwise Suitable Systems

Before approving a system, compare its installation requirements with actual project conditions:

• Can the required surface preparation be achieved?
• Can the substrate be dried or conditioned to the required level?
• Can temperature and humidity be controlled throughout cure?
• Can the ventilation system safely control vapors and spray mist?
• Can the equipment maintain the required pressure, temperature, and ratio?
• Can the required thickness be achieved on walls, ceilings, edges, and irregular surfaces?
• Is there enough time for repair, preparation, application, cure, inspection, repair, disinfection, and return to service?
• Are trained applicators and qualified inspection personnel available?

Require Written Manufacturer Confirmation

For demanding service, request written confirmation addressing:

• Exact substrate and service environment
• Normal and upset chemicals, concentrations, and temperatures
• Continuous or intermittent immersion
• Required preparation and substrate condition
• Primer, resurfacer, reinforcement, lining, and finish coats
• Required thickness for each component
• Application equipment and environmental limits
• Cure and return-to-service requirements
• Inspection, holiday testing, and repair procedures
• Warranty requirements and exclusions

Use a Complete Submittal Package

• Current technical data sheets and safety data sheets
• System application instructions
• Chemical-resistance documentation
• Applicable NSF/ANSI/CAN 61 listing and use limitations
• Relevant third-party testing and qualification data
• Surface-preparation and moisture requirements
• Application equipment and plural-component settings
• Typical details for joints, cracks, penetrations, edges, and terminations
• Inspection and repair procedures
• Written confirmation of suitability for the stated exposure

Contractor’s Selection Checklist

• Is the exact exposure defined?
• Are normal and upset conditions included?
• Is the product suitable for the substrate and exposure zone?
• Is potable-water certification required and currently valid?
• Is chemical resistance confirmed in writing?
• Can the required surface preparation and moisture condition be achieved?
• Can the crew and equipment apply the complete system correctly?
• Can environmental conditions be maintained during application and cure?
• Are cracks, joints, penetrations, and terminations fully detailed?
• Are inspection, testing, repair, and return-to-service requirements defined?
• Has the complete system—not merely a generic chemistry—been approved?

Knowledge Check

1. Does the word “epoxy” provide enough information to approve a lining?

No. Epoxy is a broad chemistry family. Approval should address the exact product, complete system, thickness, substrate, exposure, application conditions, cure, and supporting performance data.

2. What does NSF/ANSI/CAN 61 certification establish?

It establishes compliance with health-effects criteria for materials and products contacting drinking water. It does not by itself establish coating performance or suitability for a specific tank or exposure.

3. Why is a generic chemical-resistance chart insufficient?

Resistance depends on the exact formulation, chemical concentration, temperature, mixture, exposure duration, service cycle, cure, and system construction.

4. Is elastomeric a specific coating chemistry?

No. Elastomeric describes a performance characteristic. Several different coating chemistries may be formulated to provide elastomeric properties.

Technical References and Further Study

• NSF/ANSI/CAN 61, Drinking Water System Components—Health Effects. This public consensus standard establishes minimum health-effects criteria for materials, products, components, and systems contacting drinking water.
• NSF Official Certified Product Listings. Verify the current listing and use restrictions for the exact coating or lining product proposed.
• ANSI/AWWA D102-24, Coating Steel Water-Storage Tanks. This standard establishes minimum requirements for materials, coating systems, surface preparation, application, inspection, and testing of steel water-storage tanks.
• AMPP SSPC-Guide 27-2019, Recommended Performance Properties for Liquid-Applied Organic Polymeric Coatings and Linings for Municipal Wastewater Structures. This guide addresses laboratory and field performance properties for systems used on sound concrete in wastewater collection and treatment facilities.
• ASTM D7230-06 (2021), Standard Guide for Evaluating Polymeric Lining Systems for Water Immersion in Coating Service Level III Safety-Related Applications on Metal Substrates.
• ASTM C267, Standard Test Methods for Chemical Resistance of Mortars, Grouts, and Monolithic Surfacings and Polymer Concretes.
• The coating manufacturer’s current technical data sheets, safety data sheets, chemical-resistance documentation, certification listings, system details, application instructions, inspection procedures, and written confirmation of suitability.

Standards, certifications, listings, formulations, and manufacturer recommendations may change. Confirm the current documents and exact approved system before purchasing or applying materials.

Professional responsibility: This article provides foundational education and does not constitute product approval or a project-specific coating specification. Final system selection should be based on documented exposure conditions, qualified design, current manufacturer recommendations, applicable certification, contractor capability, and written owner acceptance.

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