AirSprayTech Academy Certificate Program
Secondary Containment Coating Systems for Industrial Contractors
Article 12 of 24
Vinyl Ester Containment Systems
Vinyl ester systems can provide exceptional resistance to acids, solvents,
oxidizing chemicals, permeation, and elevated-temperature service. Their performance,
however, depends on correct resin selection, controlled catalyzation, reinforcement,
application technique, cure, and inspection.
Learning Objectives
After completing this article, you should be able to:
- Explain how vinyl ester systems differ from conventional epoxy systems.
- Identify situations in which vinyl ester may be considered for secondary containment.
- Understand the functions of resin coats, fiberglass reinforcement, surfacing veil, and topcoats.
- Recognize the importance of catalyst control, temperature, working time, and exotherm.
- Identify common defects in reinforced vinyl ester linings.
- Understand why cure verification and holiday testing may be required before chemical service.
What Is a Vinyl Ester?
Vinyl ester resins are thermosetting materials produced by combining epoxy-based
chemistry with unsaturated reactive groups. They are commonly supplied as liquid
resins containing a reactive diluent and cure through a free-radical polymerization
reaction initiated by a manufacturer-approved catalyst system.
This chemistry can combine some of the toughness and adhesion associated with
epoxies with the chemical resistance and rapid cure characteristics associated
with reinforced thermosetting resin systems.
The term “vinyl ester” still describes a family of products. Resin backbone,
promoter package, fillers, reinforcement, cure system, thickness, and application
details all influence performance. A generic vinyl ester description is not a
project-specific material recommendation.
Vinyl Ester Is Not Automatically the Right Choice
Vinyl ester systems are often selected for severe chemical service, but greater
chemical resistance in one environment does not make a product suitable for every
containment area.
The manufacturer must evaluate the exact chemical, concentration, temperature,
exposure duration, substrate, mechanical conditions, cleaning procedures, and
possible chemical mixtures. Some exposures may be better served by an epoxy,
novolac epoxy, polyurethane, polyurea, fluoropolymer, rubber lining, thermoplastic
sheet lining, or another specialized system.
Obtain a written recommendation for the complete system. Do not select a vinyl
ester solely because a general chart lists a chemical as resistant.
Where Vinyl Ester Systems Are Used
Properly selected vinyl ester systems may be used in containment areas exposed to:
- Acids and acidic process solutions
- Caustics and alkaline solutions
- Solvents and hydrocarbon mixtures
- Oxidizing chemicals
- Bleach and other aggressive cleaning materials
- Chemical wastewater and process drainage
- Fertilizer, pulp-and-paper, mining, and metal-processing chemicals
- Elevated-temperature splash, spill, or immersion service
This list identifies possible applications, not universal approvals. Resistance
can change substantially with concentration, contamination, temperature, exposure
time, and the presence of other chemicals.
Vinyl Ester Compared with Epoxy
Epoxy and vinyl ester systems overlap in many applications, but their mixing,
curing, handling, and performance characteristics differ.
| Consideration |
Epoxy Systems |
Vinyl Ester Systems |
| Reaction control |
Resin and curing agent are combined at a fixed ratio. |
A promoted resin is catalyzed within a manufacturer-approved range. |
| Working time |
Varies by formulation and temperature. |
Can be short and strongly affected by temperature and catalyst level. |
| Chemical resistance |
Ranges from moderate to severe service, depending on formulation. |
Often considered for severe acids, solvents, oxidizers, and heat, subject to written approval. |
| Odor and vapor |
Depends on solvent content and formulation. |
Many formulations contain a reactive diluent and require strict ventilation and exposure control. |
| Reinforcement |
May be unreinforced or reinforced. |
Frequently used with fiberglass mat, fabric, veil, or flake reinforcement. |
These are general distinctions. The current product data and system specification
control the actual application.
Catalyst Is Not Used Like Epoxy Hardener
In a conventional two-component epoxy, the resin and curing agent are combined
at a specified ratio. With many vinyl ester systems, a relatively small quantity
of catalyst initiates the cure of a promoted resin.
The catalyst percentage may be adjusted only within the manufacturer’s stated range
to account for material and substrate temperature. Too little catalyst can cause
slow, incomplete, or unreliable cure. Too much can produce excessive heat, very
short working time, poor application, cracking, or other defects.
Contractors must use the catalyst type, measurement method, mixing sequence,
and percentage specified by the system manufacturer. Substituting catalysts or
altering the recommended chemistry is not acceptable.
Catalyst Safety Requires Formal Control
Organic-peroxide catalyst systems can present serious fire, decomposition,
contamination, and personal-exposure hazards. Catalyst must be stored, handled,
dispensed, and disposed of according to the manufacturer’s safety data sheet
and applicable regulations.
- Use dedicated, clean measuring and dispensing equipment.
- Keep catalyst away from heat, sparks, flame, sunlight, and incompatible materials.
- Do not return unused catalyst to its original container.
- Do not mix catalyst directly with promoters, accelerators, or contaminants.
- Prevent spills and uncontrolled contact with absorbent or combustible materials.
- Use the required eye, skin, respiratory, and protective equipment.
- Train workers in the site-specific emergency procedure before work begins.
Typical Components of a Reinforced Vinyl Ester System
A reinforced system may contain several layers, each with a specific function:
-
Primer:
Promotes adhesion to properly prepared concrete or steel and provides
a compatible base for the laminate.
-
Body or base coat:
Provides resin for embedding and saturating reinforcement.
-
Fiberglass reinforcement:
May include chopped-strand mat, woven fabric, stitched fabric, or another
specified reinforcement to increase strength and distribute stress.
-
Surfacing veil:
Provides a resin-rich corrosion barrier and helps prevent coarse reinforcement
from reaching the exposed surface.
-
Seal or topcoat:
Provides the final chemical-contact surface, seals exposed fibers, and may
contain wax or another additive required for complete surface cure.
Layer sequence, reinforcement type, overlap, thickness, and resin content must
follow the approved system specification.
Unreinforced and Flake-Filled Systems
Not every vinyl ester lining uses fiberglass mat. Some systems are applied as
flake-filled or mineral-filled coatings. Plate-like fillers can create a more
tortuous path through the cured film and may improve resistance to permeation,
abrasion, or thermal service.
These materials may be spray applied, rolled, brushed, squeegeed, or troweled,
depending on viscosity and system design. Their required thickness may be greater
than that of ordinary protective coatings.
An unreinforced system may be appropriate for a stable substrate and defined
exposure but may not provide the same crack-distribution or stress-handling
capability as a properly installed reinforced laminate.
Surface Preparation and Primer Compatibility
Vinyl ester systems do not compensate for weak concrete, laitance, contamination,
moisture problems, corrosion, dust, or an incorrect surface profile. Concrete and
steel must be prepared to the system manufacturer’s requirements and accepted
before application begins.
The primer must be compatible with both the substrate and vinyl ester laminate.
An epoxy primer should not be substituted beneath a vinyl ester system unless the
manufacturer has approved the complete combination and its recoat procedure.
Previously coated surfaces require special evaluation. Solvent resistance,
adhesion testing, contamination, existing film thickness, and compatibility must
be considered before any overcoating recommendation is accepted.
Batch Size, Gel Time, and Working Time
Vinyl ester reaction speed is affected by resin temperature, substrate temperature,
air temperature, catalyst percentage, batch size, container shape, and the
manufacturer’s promoter system.
A large mass of catalyzed resin can generate heat and cure much faster than the
same material spread in a thin film. Material remaining in a mixing pail may gel
or exotherm while the applied film remains workable.
The crew should establish expected working time with a controlled field test or
gel-time check when required. Mix only the quantity that can be installed,
reinforced, consolidated, and detailed before cure advances too far.
Never attempt to extend working time by adding unapproved solvent, monomer,
catalyst, or uncatalyzed resin.
Installing Fiberglass Reinforcement
Fiberglass reinforcement must be completely wetted with resin and consolidated
without leaving air pockets, wrinkles, folds, lifted edges, resin-starved areas,
or unsupported bridging.
A typical installation sequence may include:
- Apply the specified resin-rich base coat.
- Place the reinforcement while the resin remains workable.
- Apply additional resin as required to wet the reinforcement.
- Use approved rollers or tools to remove trapped air and consolidate the laminate.
- Maintain the specified overlap between adjacent pieces.
- Feather or stagger laps as required to avoid excessive ridges.
- Inspect the wet laminate under strong lighting before it cures.
- Repair dry, lifted, wrinkled, or air-filled areas according to the approved procedure.
The objective is not merely to hide fiberglass beneath resin. The completed laminate
must contain the correct reinforcement-to-resin relationship and form a continuous,
well-bonded barrier.
Why a Resin-Rich Corrosion Barrier Matters
The chemical-contact surface of a reinforced laminate should contain a resin-rich
layer that separates the chemical exposure from the structural reinforcement.
Surfacing veil can help create this corrosion barrier.
Exposed or insufficiently covered fibers can wick liquid, create permeation paths,
and produce localized attack. Sanding, grinding, or aggressive finishing can
accidentally expose reinforcement and reduce the protective resin layer.
After any surface correction, restore the specified veil, seal coat, and topcoat
before placing the system into service.
Air Inhibition and Final Surface Cure
Some vinyl ester resins remain tacky at an air-exposed surface because oxygen can
inhibit complete surface cure. That characteristic can assist bonding between
laminate layers applied within the approved interval.
The final chemical-contact surface may require a wax-containing topcoat or another
manufacturer-specified surfacing treatment to achieve complete cure. Wax rises to
the surface and limits oxygen contact while the resin cures.
A waxed surface can interfere with later adhesion. If another layer or repair must
be applied, the wax or inhibited layer may need to be removed by washing, sanding,
or another specified method. Follow the written repair procedure.
Details, Transitions, and Terminations
Containment failures frequently begin at drains, penetrations, wall-to-floor
transitions, equipment bases, embedded steel, joints, curbs, pipe supports,
termination edges, and changes in substrate.
Reinforcement should conform to the detail without bridging or lifting. Sharp
inside corners may require coves. Outside corners may require rounding and
additional reinforcement. Terminations may require a chase, reglet, mechanical
anchor, sealant, or other engineered detail.
Do not improvise critical transition details in the field. Obtain approved drawings
and procedures before application reaches those locations.
Film and Laminate Thickness
Thickness is part of the system design. It can affect chemical permeation,
reinforcement coverage, mechanical performance, crack distribution, and
holiday-testing voltage.
Thickness should be checked at the frequency and by the method required by the
specification. Measurement may involve wet-film checks, material usage,
controlled sample panels, destructive measurements, dry-film instruments on
suitable substrates, or other approved procedures.
More material is not automatically better. Excess resin can drain, sag, crack,
exotherm, or create resin-rich areas without proper reinforcement. Insufficient
resin can leave dry fibers, voids, and inadequate chemical protection.
Cure Verification
A lining may appear hard without having developed the cure needed for chemical
service. Cure verification should follow the manufacturer’s approved method and
the project specification.
Verification may include:
- Recorded cure time and actual temperature history
- Visual and tactile examination
- Surface tack evaluation
- Solvent-rub testing when approved
- Barcol hardness measurements on suitable rigid systems
- Manufacturer or laboratory testing when required
Barcol hardness is not a universal pass-or-fail test for every vinyl ester lining.
The correct instrument, minimum value, test timing, number of readings, and
interpretation must come from the specification or manufacturer.
Holiday and Discontinuity Testing
Pinholes, voids, exposed fibers, cuts, and missed areas can permit chemicals to
reach the substrate. Holiday testing may therefore be required after the lining
has cured sufficiently and before the area is placed into service.
The test method and voltage must be appropriate for the lining thickness,
substrate, system, and specification. Excessive voltage can damage a sound lining.
Insufficient voltage may fail to locate a discontinuity.
Mark each detected holiday without causing additional damage. Repair it using
the approved procedure, allow the repair to cure, and retest the repaired area.
A repair is not complete until it passes the required inspection.
Common Vinyl Ester Defects
-
Dry reinforcement:
Insufficient resin saturation leaves white, light-colored, or visibly dry fibers.
-
Air pockets and voids:
Inadequate consolidation traps air beneath or within the reinforcement.
-
Wrinkles and lifted laps:
Poor placement, rapid cure, difficult geometry, or insufficient wetting prevents
the reinforcement from lying flat.
-
Soft or undercured material:
Incorrect catalyst level, poor mixing, low temperature, contamination,
or chemical exposure before complete cure.
-
Cracking or excessive heat damage:
Over-catalyzation, excessive batch size, thick resin accumulation,
or uncontrolled exotherm.
-
Delamination:
Contamination, improper preparation, moisture, incompatible layers,
or application outside the permitted recoat interval.
-
Exposed fibers:
Insufficient corrosion-barrier resin, aggressive sanding, wear,
or incomplete topcoating.
-
Chemical attack:
Incorrect resin selection, incomplete cure, excessive temperature,
greater concentration, prolonged exposure, or an unanticipated mixture.
Ventilation, Vapor, and Fire Safety
Many vinyl ester systems release vapors that require controlled ventilation,
exposure monitoring, suitable respiratory protection, and ignition control.
Odor is not a reliable measure of safe exposure.
Ventilation must move vapor away from workers and the work area without introducing
dust, moisture, exhaust, or other contamination into the wet lining. Electrical
equipment, lighting, fans, and tools must be appropriate for the classified hazard.
Review the current safety data sheets for the resin, catalyst, cleaners, solvents,
and repair materials. Confined-space entry requirements apply whenever the work area
meets the regulatory definition.
Field Quality-Control Checklist
- Written system approval matches the chemical exposure and temperature.
- Resin, catalyst, fillers, reinforcement, veil, and topcoat match the specification.
- Product batch numbers and shelf lives are recorded.
- Storage and material temperatures are within the required range.
- Surface preparation and primer have been inspected and accepted.
- Catalyst type, amount, and measurement method are verified.
- Batch size and working time are controlled.
- Fiberglass is fully wetted and properly consolidated.
- Laps, corners, transitions, penetrations, and terminations follow approved details.
- Required thickness and resin-rich corrosion barrier are achieved.
- No dry fibers, air pockets, wrinkles, voids, or exposed reinforcement remain.
- Cure has been verified by the specified method.
- Holiday testing and repairs have been completed and documented.
- Full chemical-service cure has been reached before release to service.
Technical References
Use the editions identified in the contract documents and verify current
designations before incorporating standards into a proposal or work plan.
Key Takeaways
- Vinyl ester systems can provide severe chemical and temperature resistance.
- The generic resin name does not establish suitability for a specific exposure.
- Catalyst measurement and mixing require precise control.
- Catalyzed material can generate significant heat and lose working time rapidly.
- Fiberglass must be fully wetted and consolidated without voids or dry fibers.
- The chemical-contact surface requires a continuous resin-rich corrosion barrier.
- Cure verification must follow the specified method.
- Holiday testing and documented repairs help confirm lining continuity.
- Written manufacturer approval should address the entire exposure and complete system.
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 manufacturer’s current written recommendation.
Vinyl ester resins, catalysts, solvents, and related materials may present serious
fire, vapor, exposure, and reaction hazards. Review current technical data sheets,
safety data sheets, catalyst instructions, application procedures, ventilation
requirements, and site-safety plans before beginning work.
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