AirSprayTech Academy Certificate Program

Secondary Containment Coating Systems for Industrial Contractors

Article 11 of 24

Epoxy and Novolac Epoxy Containment Systems

Epoxy systems are widely used for secondary containment, but the word “epoxy” does not identify a single level of performance. Resin type, curing agent, reinforcement, film thickness, exposure, temperature, and application quality determine what an epoxy system can safely contain.

Learning Objectives

After completing this article, you should be able to:

• Explain why epoxy products do not all provide the same chemical resistance.
• Distinguish conventional epoxy systems from novolac epoxy systems.
• Identify the exposure information required before selecting a containment lining.
• Recognize the strengths and limitations of high-build and solvent-free epoxy linings.
• Understand how mixing, temperature, film thickness, cure, and inspection affect performance.
• Use manufacturer chemical-resistance data without treating a general resistance chart as a final approval.

“Epoxy” Describes a Family of Materials

Epoxy coatings are thermosetting materials. A resin component reacts with a curing-agent component to form a cross-linked film. Once properly cured, that film cannot be returned to its original liquid state by adding solvent.

The properties of the finished lining depend on much more than the epoxy label. Important variables include the resin structure, curing-agent chemistry, pigment and filler package, solvent content, reinforcement, mixing ratio, cure conditions, and final cross-link density.

Two products described as chemical-resistant epoxies may perform very differently when exposed to the same acid, caustic, solvent, fuel, wastewater, or process chemical. Product selection must be based on the complete exposure and the manufacturer’s written recommendation for that exact service.

Chemical Name Alone Is Not Enough

It is not enough to tell a lining manufacturer that the containment area will hold “acid,” “fuel,” “solvent,” or “wastewater.” Selection requires specific, written exposure information.

• Exact chemical or product name
• Concentration or expected concentration range
• Normal and maximum temperatures
• Expected spill duration
• Splash, intermittent exposure, or continuous immersion
• Single chemical or chemical mixture
• Possible reaction between materials entering the containment area
• Frequency and method of cleaning or decontamination
• Mechanical traffic, abrasion, impact, or thermal cycling

A change in concentration, temperature, contaminants, or exposure duration can change the recommendation. Written approval should identify the complete lining system—not simply a generic resin family.

Conventional Epoxy Systems

Conventional industrial epoxies are frequently used where good adhesion, toughness, abrasion resistance, water resistance, and moderate chemical resistance are required. Formulations may be based on bisphenol-A, bisphenol-F, or modified epoxy resins combined with amine, amine-adduct, polyamide, or other curing agents.

These systems may be appropriate for oils, lubricants, water, wastewater, dilute chemicals, and many splash-and-spill exposures when specifically approved. They are available as thin-film coatings, high-build coatings, self-leveling materials, mortars, laminates, and reinforced systems.

A conventional epoxy should not be assumed suitable for strong acids, aggressive solvents, oxidizing chemicals, or elevated-temperature exposure. Those conditions may require a more highly cross-linked epoxy, a novolac epoxy, a vinyl ester, or another specialized lining technology.

Novolac Epoxy Systems

Novolac epoxies are formulated to develop a higher cross-link density than many conventional epoxies. The more tightly cross-linked structure can improve resistance to certain acids, solvents, fuels, and elevated-temperature exposures.

That does not make every novolac epoxy resistant to every chemical. Different products use different resins, curing agents, fillers, and reinforcement. Performance also depends on concentration, temperature, duration, film thickness, and whether exposure is intermittent or continuous.

Higher cross-link density can also produce a harder, less flexible film. Movement, cracking, vibration, impact, or thermal cycling may require reinforcement, elastomeric detailing, flexible transition materials, or a different system design.

Novolac epoxy is a valuable containment technology, but it must be selected as part of an engineered system—not as a universal upgrade based only on its name.

Cross-Link Density: Performance and Tradeoffs

Cross-link density describes how closely the cured polymer network is connected. A tightly cross-linked coating can make it more difficult for certain chemicals to penetrate and attack the film.

However, performance is not determined by cross-link density alone. A formulation must balance chemical resistance with adhesion, toughness, flexibility, impact resistance, application properties, and the ability to tolerate actual substrate movement.

A very chemically resistant lining can still fail if concrete cracks beneath it, steel flexes, a joint moves, the film contains pinholes, or the material was not allowed to cure completely before exposure.

High-Solids and Solvent-Free Epoxies

High-solids and solvent-free epoxies can produce substantial film thickness with fewer coats than conventional solvent-containing coatings. They can reduce solvent emissions, shrinkage, and solvent entrapment when properly selected and applied.

These materials may also be more demanding to install. Higher viscosity can require specialized pumps, larger fluid passages, heated components, plural-component proportioning equipment, or carefully controlled material temperatures.

A product described as 100-percent solids does not automatically provide superior chemical resistance. Solids content describes how much material remains after cure; it does not, by itself, identify the cured polymer’s resistance to a specific chemical.

Film thickness must remain within the manufacturer’s approved range. Excessive application can generate heat during cure, trap air, sag, crack, or leave an improperly cured film. Thin application can leave profile peaks, pores, and irregularities insufficiently protected.

Flake-Filled and Reinforced Epoxy Systems

Some epoxy and novolac epoxy linings contain glass flake, mineral flake, ceramic fillers, fibers, or other reinforcement. Properly formulated fillers can increase the path that chemicals must travel through the lining and may improve abrasion, thermal, or permeation resistance.

Other systems use fiberglass mat, woven fabric, chopped strand, or scrim embedded in resin. Reinforcement can help distribute stress and bridge minor irregularities, but it does not make an active structural crack harmless.

Reinforced systems require careful saturation, consolidation, overlap, termination, and inspection. Dry reinforcement, trapped air, lifted edges, resin-starved areas, and exposed fibers can create leakage paths or early failure points.

Splash-and-Spill Versus Continuous Immersion

Secondary containment normally receives material after a leak, spill, or equipment failure. That does not mean exposure will always be brief. A spill can remain in a dike overnight, through a weekend, or longer while personnel identify the material and arrange safe recovery.

Chemical-resistance documents may distinguish among fumes, splash, spillage, intermittent contact, and continuous immersion. A rating for splash-and-spill exposure should not be treated as approval for immersion.

The owner should establish the maximum anticipated time before a release will be detected, removed, and the surface cleaned. The manufacturer’s recommendation should match that realistic containment period.

Mixtures Can Be More Aggressive Than Individual Chemicals

A containment area may receive chemicals from multiple tanks, pipes, transfer points, or processes. Materials that are compatible with a lining individually may create a more aggressive mixture when combined.

Mixing can generate heat, change pH, create new reaction products, release vapor, or increase penetration into the lining. Water introduced during emergency response or cleanup can also change chemical concentration and temperature.

When mixtures are possible, obtain written guidance based on the anticipated combined exposure. A chemical-resistance chart for one pure substance does not answer the mixture question.

Temperature Changes Chemical Resistance

Chemical attack generally becomes more severe as temperature increases. A lining that performs satisfactorily at room temperature may soften, swell, discolor, blister, or lose adhesion at an elevated temperature.

The important value is not only the normal operating temperature. Selection should consider the maximum spill temperature, cleaning temperature, steam exposure, sun-heated surface temperature, and temperature generated by a chemical reaction.

Dry-temperature ratings must not be confused with chemical immersion ratings. A coating capable of tolerating high temperature in dry air may have a much lower allowable temperature when exposed to a particular liquid.

Substrate Movement and Crack Bridging

Most cured epoxy linings are relatively rigid. They may tolerate limited strain, but they should not automatically be expected to bridge moving cracks, expansion joints, differential movement, or significant thermal cycling.

Concrete cracks must be evaluated to determine whether they are dormant or active. Dormant cracks may be repaired and incorporated into the lining system. Active cracks and joints normally require a flexible detail designed for the expected movement.

Do not rigidly coat a functioning expansion joint unless the system manufacturer and project designer provide an approved detail. The strongest epoxy cannot stop a structure from moving.

Mixing and Proportioning

Epoxy chemistry depends on the correct relationship between resin and curing agent. Incorrect proportioning can leave unreacted components in the film and cause soft areas, poor chemical resistance, surface contamination, loss of adhesion, or incomplete cure.

For batch-mixed materials:

• Condition components to the specified temperature.
• Use complete kits whenever practical.
• Pre-mix individual components when required.
• Combine components at the stated ratio.
• Mix with the specified equipment, speed, and duration.
• Scrape container sides only as directed by the manufacturer.
• Observe any required induction time.
• Record the mixing time and discard material when its working life expires.

When partial kits are expressly permitted, components must be measured with accurate, suitable equipment. Guessing by volume or dividing material based on container height is not reliable.

Plural-Component Application

Fast-reacting or very high-solids epoxy systems may require plural-component equipment. The machine meters resin and curing agent separately and combines them at or near the mix manifold.

The crew must verify proportioning accuracy, material temperatures, pressures, heater settings, hose condition, mixer configuration, tip size, spray pattern, and shutdown or flushing procedures.

A smooth spray pattern does not prove that the material is being proportioned correctly. Ratio checks and equipment verification must be performed at the intervals required by the manufacturer, specification, and quality-control plan.

Pot Life Is Not the Same as Cure Time

Pot life describes the useful working period after components are combined. Recoat time describes when another layer may be applied. Cure time describes the development of the coating’s physical properties. Chemical-service cure identifies when the system has developed sufficient resistance for the specified exposure.

These are different time periods. A lining may feel hard and support foot traffic while remaining chemically vulnerable. Introducing chemicals before full chemical-service cure can permanently damage the system.

Temperature strongly affects reaction rate. Cold conditions can delay cure, while high material temperatures can shorten pot life and working time. Cure schedules must be based on actual substrate and environmental conditions.

Film Thickness and Number of Coats

The specified dry-film thickness is part of the system design. It should not be reduced simply because the surface appears covered. Chemical resistance, permeation resistance, holiday-free continuity, and service life may depend on achieving the approved thickness.

Multiple coats can reduce the chance that pinholes in one coat will align with discontinuities in another. Contrasting colors may help the applicator and inspector identify thin or missed areas.

Some high-build or plural-component products are designed for single-coat application. Others require two or more coats, reinforcement, mortar, or a separate topcoat. Follow the specified system rather than substituting an unapproved number of coats.

Common Epoxy Application Defects

• Soft or uncured material: Incorrect ratio, incomplete mixing, contamination, low temperature, or application beyond working life.
• Pinholes and bubbles: Concrete outgassing, entrained air, porous substrate, poor application timing, or inadequate primer and detail work.
• Runs and sags: Excessive film thickness, incorrect temperature, overthinning, or unsuitable spray technique.
• Dry spray or poor wetting: Incorrect pressure, excessive gun distance, unsuitable tip, cold material, or poor access.
• Intercoat delamination: Contamination, amine blush, an exceeded recoat window, or insufficient preparation between coats.
• Cracking: Excessive thickness, substrate movement, thermal stress, impact, shrinkage, or a system too rigid for the service.
• Chemical attack: Incorrect material selection, incomplete cure, unexpected temperature, greater concentration, longer exposure, or an unanticipated chemical mixture.

Field Quality-Control Checklist

• Written manufacturer approval matches the complete exposure.
• Specified primer, lining, reinforcement, detail materials, and topcoat are available.
• Product names, batch numbers, colors, and shelf lives are recorded.
• Surface preparation has been inspected and accepted.
• Environmental and substrate conditions are within product limits.
• Mixing or plural-component ratio is verified.
• Material is applied within its working time.
• Required stripe coats and detail treatments are complete.
• Wet- and dry-film thicknesses comply with the specification.
• Recoat windows are tracked by area.
• Defects are identified, repaired, and reinspected.
• Holiday testing is completed when specified.
• The full chemical-service cure is documented before release to service.

Technical References

Use the editions identified in the project documents and verify current designations before placing requirements into a proposal or work plan.

• AMPP — Coatings and Linings over Concrete for Chemical Immersion and Containment Service
• AMPP — Linings over Concrete for Immersion Service
• ASTM D6943 — Standard Practice for Immersion Testing of Industrial Protective Coatings and Linings
• U.S. EPA — Concrete Liners for Hazardous-Waste Tank Systems
• Carboline Tank-Lining Chemical-Resistance Chart and Product Overview
• AMPP SP0188: Discontinuity holiday testing of protective coatings and linings.
• Manufacturer documentation: Current technical data sheets, safety data sheets, chemical-resistance guides, system specifications, application instructions, and written project-specific recommendations.

Key Takeaways

• The word “epoxy” does not establish chemical resistance.
• Novolac epoxies can provide increased resistance, but they are not universal solutions.
• Chemical, concentration, temperature, duration, and exposure type must all be identified.
• Mixtures and reaction temperatures require separate consideration.
• A 100-percent-solids description does not prove chemical compatibility.
• Rigid epoxy systems require proper treatment of cracks, joints, and moving transitions.
• Correct proportioning and full chemical-service cure are essential.
• Written, project-specific manufacturer approval should support final system selection.

Professional responsibility: This article provides foundational educational information and is not a substitute for the project specification, engineering direction, regulatory requirements, chemical-resistance testing, or the coating manufacturer’s current written recommendation. Always obtain approval based on the exact chemical, concentration, temperature, exposure duration, substrate, and complete proposed system. Review current technical data sheets, safety data sheets, application instructions, and site-safety requirements before beginning work.

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