When Conventional Epoxy May Not Be Enough

Conventional epoxy linings serve many industrial applications, but some tanks and process vessels operate under chemical or temperature conditions that require a more highly crosslinked material. Novolac epoxy linings are one option developed for certain demanding services.

Depending on their formulation, novolac epoxies may provide improved resistance to selected acids, solvents, fuels, elevated temperatures, and other aggressive exposures when compared with some conventional epoxy systems.

That does not make every novolac product universally chemical-resistant. Novolac epoxies still have specific chemical, concentration, temperature, substrate, film-thickness, application, and cure limits.

What Makes a Novolac Epoxy Different?

Epoxy performance is influenced by the structure of the resin, curing agent, pigments, fillers, reinforcement, crosslink density, and the quality of the completed cure.

Novolac epoxy resins generally offer more potential reaction sites than common conventional epoxy resins. When properly formulated and cured, this can produce a tighter three-dimensional network with increased crosslink density.

The tighter network may reduce the ability of certain chemicals to enter or move through the cured lining. It may also help the lining retain useful properties at temperatures or in chemical environments that exceed the limits of some conventional epoxies.

Higher crosslink density can also produce a harder and less flexible film. This makes substrate movement, excessive film build, sharp details, thermal cycling, and application quality especially important.

Conventional Epoxy Compared With Novolac Epoxy

This comparison is general. Actual performance must be taken from the current data for the exact products under consideration.

Where Novolac Epoxy Linings May Be Used

Novolac epoxy systems may be considered for demanding areas such as:

• Chemical-storage tanks
• Process vessels and reactors
• Selected acid and alkali containment
• Fuel, hydrocarbon, and selected solvent service
• High-temperature water and process liquids
• Aggressive wastewater environments
• Secondary containment areas
• Trenches, sumps, pits, and process floors
• Pulp and paper processing areas
• Mining, mineral-processing, and power facilities

Inclusion in this list does not establish suitability. The lining manufacturer must evaluate the exact chemical, concentration, temperature, exposure type, substrate, and cleaning conditions.

Obtain Service-Specific Written Approval

A chemical-resistance chart is useful for screening possible materials, but it may not represent the complete project condition. Ratings can be based on different test durations, film builds, temperatures, cure conditions, and acceptance criteria.

Provide the manufacturer with:

• Exact chemical or product name
• Concentration and possible variation
• Normal and maximum temperatures
• Immersion, intermittent, splash, spill, or vapor exposure
• Expected exposure duration
• Mixtures, contaminants, and process by-products
• Cleaning chemicals and procedures
• Abrasion, impact, agitation, and flow
• Steel, concrete, or other substrate
• Required cure and return-to-service schedule

Important Limitations

Higher Resistance Is Not Universal Resistance

A novolac epoxy may outperform a conventional epoxy in one chemical but remain unsuitable for another. Oxidizing chemicals, strong solvents, mixtures, impurities, and elevated temperature can change performance.

Hardness Can Reduce Movement Tolerance

A highly crosslinked lining can be relatively rigid. Cracking, flexing, vibration, thermal cycling, poorly detailed welds, and concrete movement can place stress on the lining.

Film Thickness Must Be Controlled

Insufficient thickness can reduce barrier performance. Excessive thickness may increase internal stress, slow cure, trap solvent or air, and contribute to cracking or other defects.

Cure Is Part of Chemical Resistance

The properties expected from a novolac epoxy depend on the chemical reaction reaching the required state of cure. An undercured lining may not provide the chemical or temperature resistance shown in product data.

Surface Preparation Is Still the Foundation

Advanced resin chemistry cannot overcome contamination, weak concrete, soluble salts, insufficient profile, dust, moisture, sharp edges, weld defects, or poor repairs.

Prepare steel or concrete to the project specification and current manufacturer instructions. Verify cleanliness, surface profile, moisture, contaminants, repairs, and environmental conditions before material is applied.

Mixing and Application Controls

Novolac epoxy products may be high in solids, heavily filled, or formulated for high film build. Some can be applied with conventional airless equipment, while others may require heated hoses, larger pumps, special spray components, or plural-component equipment.

Confirm the following before application:

• Component ratio and package size
• Required material-storage temperature
• Mixing equipment and mixing time
• Induction time, if required
• Pot life at the actual material temperature
• Approved thinner and maximum permitted amount
• Pump, hose, gun, and spray-tip requirements
• Required stripe-coating procedure
• Wet-film and dry-film thickness limits
• Recoat and cure requirements

Pot Life Can Change Quickly

Material temperature has a major effect on working time. Warm material may spray more easily but react faster. A large quantity left in a mixing container can develop heat and lose usable pot life more quickly than material spread across a surface.

Do not attempt to restore expired material by adding thinner, solvent, or fresh material. Dispose of expired material according to project, manufacturer, safety, and environmental requirements.

Protect Edges, Welds, and Difficult Details

Sharp edges, irregular welds, pits, bolts, penetrations, and complex details are difficult to cover uniformly. These areas can become thin spots and starting points for chemical attack.

Complete required grinding, filling, fairing, and stripe coating before the full lining coats. Follow the specified sequence so stripe coats become properly integrated into the lining system.

Recoat Windows and Final Cure

Highly crosslinked materials may develop a hard surface that becomes more difficult to recoat after the maximum recoat time. If the window is exceeded, the surface may require cleaning and mechanical preparation before the next coat or repair is applied.

Final cure must be based on actual substrate and material temperatures, not only the calendar. Cold steel, shaded areas, heavy film, restricted ventilation, and low nighttime temperatures may extend the cure period.

Inspection Requirements

Inspection may include:

• Visual examination for sags, pinholes, cracks, contamination, and missed areas
• Verification of dry-film thickness
• Holiday or discontinuity testing
• Adhesion testing where specified
• Hardness or cure verification where specified
• Inspection of repairs and repair boundaries
• Review of environmental, mixing, application, and cure records

Common Installation Problems

Safety Considerations

Novolac epoxy resins, curing agents, solvents, thinners, cleaning materials, and spray mist can create skin, eye, respiratory, fire, and other hazards. Review the current Safety Data Sheet for every component and supporting chemical used on the project.

Tank and vessel work may involve permit-required confined spaces. Follow applicable requirements for isolation, atmospheric testing, ventilation, respiratory protection, protective clothing, communication, attendants, rescue, ignition control, high-pressure equipment, and waste handling.

The Key Takeaway

Novolac epoxy linings may provide enhanced chemical and temperature resistance for selected severe services. Their potential comes from formulation and a highly crosslinked cured film.

That performance is only achieved when the correct product is selected, the substrate is properly prepared, components are mixed accurately, film thickness and recoat windows are controlled, and the lining receives its full specified cure before service.

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