AirSprayTech Academy Certificate Program
Secondary Containment Coating Systems for Industrial Contractors
Article 16 of 24
Mixing, Staging, Induction Time, and Pot Life
Containment linings depend on controlled chemistry. Accurate proportioning,
complete mixing, organized staging, temperature control, and strict observance
of working time are essential to producing a fully cured and chemically resistant system.
Learning Objectives
After completing this article, you should be able to:
- Organize a controlled material-staging and mixing area.
- Verify product identity, batch numbers, shelf life, and storage condition.
- Distinguish mixing time, induction time, pot life, working time, and cure time.
- Understand why temperature and batch size affect material behavior.
- Recognize common proportioning and mixing errors.
- Document each batch so questionable material can be traced to its installed location.
Mixing Is a Quality-Control Operation
Mixing is not simply the act of stirring two liquids together. It is the controlled
start of a chemical reaction. Once components are combined, the crew has a limited
period to move, apply, finish, inspect, and correct the material.
Incorrect proportioning or incomplete mixing can produce material that looks
acceptable during application but remains soft, becomes brittle, loses adhesion,
or lacks the chemical resistance expected from the system.
A trained person should be assigned responsibility for material control. That
person should understand the product data sheet, mixing ratio, equipment,
induction time, pot life, temperature limitations, and project documentation.
Never Guess at the Mixing Ratio
Two-component materials are formulated with a specific relationship between
resin and curing agent. Changing that relationship does not normally make the
material cure faster or slower in a controlled manner. It leaves excess unreacted
material in the cured film.
Mixing ratios may be expressed by volume, weight, or complete packaged units.
A ratio stated by volume must not be converted to weight without manufacturer
data because the components may have different densities.
Use complete kits whenever practical. Divide kits only when the manufacturer
permits it and accurate, clean measuring equipment and a written procedure are available.
Establish a Controlled Mixing Station
The mixing station should be positioned close enough to support production but
far enough from prepared and coated surfaces to prevent contamination.
A properly arranged station should include:
- Weather protection and adequate ventilation
- Clean, level work surfaces
- Secondary containment beneath stored and mixed materials
- Organized separation of resin, curing agent, catalyst, solvent, and waste
- Suitable lighting for reading labels and observing mixing
- Approved mixers, measuring containers, timers, and temperature instruments
- Batch-control forms or electronic records
- Spill-control materials and waste containers
- Required personal protective equipment
- Fire extinguishers and ignition control where required
- A method for preventing unauthorized material changes
Material Receiving and Verification
Materials should be inspected when they arrive at the project. Do not wait until
application begins to discover that a component is missing, damaged, expired,
frozen, overheated, or from an unapproved batch.
Verify and record:
- Manufacturer and product name
- Component designation
- Color and system layer
- Container size and quantity
- Batch or lot number
- Manufacturing or expiration date
- Container condition and seal integrity
- Required storage temperature
- Approval against the project submittal
Quarantine questionable material until the manufacturer or responsible authority
provides written direction. Do not blend an unapproved batch into the work simply
to avoid delay.
Storage and Material Conditioning
Storage temperature affects viscosity, mixing, atomization, reaction rate, pot life,
and cure. Material that has been stored outside its permitted range may require
controlled conditioning or may no longer be suitable for use.
Cold material may be too viscous to mix or pump correctly. Warm material may react
rapidly and lose working time. Direct flame, uncontrolled heaters, and excessive
localized heat should never be used to condition coating material.
Condition entire containers gradually in an approved temperature-controlled area.
Measure actual material temperature rather than assuming it matches the surrounding air.
Important Time Definitions
-
Mixing time:
The required period for combining components into a uniform material.
-
Induction time:
A waiting period required after components are mixed and before application begins.
-
Pot life:
The period during which mixed material remains usable under stated conditions.
-
Working time:
The practical period during which material can be applied and properly finished
under actual field conditions.
-
Gel time:
The period before a reacting material reaches a gelled condition.
-
Recoat window:
The permitted time range for applying the next layer without additional preparation.
-
Cure time:
The time required to develop a stated level of physical properties.
-
Chemical-service cure:
The time required before the system may be exposed to the specified chemical service.
Induction Time
Some coatings require an induction or sweat-in period after mixing. This allows
the chemical reaction to advance to the point required for proper application
and cure.
Induction time may change with material temperature. Starting application too
soon can affect film formation, cure, or performance. Waiting too long consumes
part of the available pot life.
Start a timer when mixing is completed and label the container with the mix time,
induction-complete time, and discard time. Do not rely on memory.
Pot Life Is Temperature Dependent
Published pot life is normally based on a stated material quantity and temperature.
A product with a 45-minute pot life under laboratory conditions may provide
substantially less working time in a hot containment area.
Larger batches retain reaction heat and may cure faster. Material left in a deep
pail can become hot or gel while the same material spread over a floor remains workable.
Plan batch size around the actual crew, geometry, application method, temperature,
and travel distance from the mixing station. A smaller controlled batch is better
than a large batch the crew cannot place in time.
Do not apply material merely because it still appears liquid. A product can exceed
its usable pot life without becoming visibly solid.
Never Add Solvent to Restore Expired Material
Adding solvent to material that has begun to react may reduce viscosity temporarily,
but it does not reverse the chemical reaction or restore the original pot life.
Unauthorized thinning can change film thickness, sag resistance, cure, volatile
content, chemical resistance, and compliance with environmental requirements.
Use only the thinner named by the manufacturer, only within the stated limit,
and only when the project specification permits it. Record every addition.
Pre-Mixing Individual Components
Pigments, fillers, aggregate, or other solids may settle during storage. The
manufacturer may require an individual component to be pre-mixed before it is
combined with the other component.
Pre-mix until the component is uniform and settled material has been incorporated.
Do not introduce excessive air or scrape dried skin, debris, or contamination
from the container into the product.
Some moisture-sensitive or clear components may not require or permit unnecessary
agitation. Follow the product-specific instructions rather than assuming every
container should be mixed the same way.
Proper Mixing Technique
- Confirm the correct product, components, ratio, and batch size.
- Measure and record component temperatures.
- Pre-mix individual components when required.
- Place the measured components into a clean, suitable container.
- Use the specified mixer blade and drill speed.
- Keep the mixer submerged to reduce air entrainment.
- Move the blade throughout the material without striking the container.
- Mix for the full specified time.
- Transfer to a clean container and remix when the procedure requires double-potting.
- Add approved aggregate, filler, or thinner only in the specified sequence.
- Begin and record any required induction period.
- Label the mixed batch with its mix time and discard time.
Avoid Unmixed Material from the Container
Unmixed resin or curing agent can remain along the sides and bottom of the mixing
container. If this material is scraped into the application equipment, it can
create soft spots or uncured streaks.
When double-potting is required, transfer the mixed material into a clean container
and mix again. This reduces the likelihood of unmixed material entering the work.
Do not scrape partially mixed residue from the original container into the new
container unless the approved procedure specifically requires it.
Vinyl Ester Catalyst Control
Many vinyl ester materials use a promoted resin and a relatively small amount
of catalyst. The catalyst percentage may be adjustable only within a manufacturer-approved
range based on actual material temperature.
Small measuring errors can become significant. Use clean, dedicated, accurately
graduated equipment. Never estimate catalyst quantity by counting unverified pours,
capfuls, or container markings.
Catalyst can present serious fire, reaction, contamination, and personal-exposure
hazards. Follow the current safety data sheet and keep catalyst away from heat,
ignition sources, incompatible chemicals, promoters, and contaminated tools.
Plural-Component Proportioning
Plural-component equipment separately conditions, meters, pressurizes, and
delivers components before they are combined. Accurate proportioning depends
on the entire material-delivery system.
The operator should verify:
- Correct pump ratio and configuration
- Material temperatures and viscosities
- Feed-pump operation and component supply
- Balanced operating pressures
- Heater and heated-hose settings
- Mix-manifold and static-mixer configuration
- Correct gun, chamber, nozzle, or spray-tip selection
- Ratio-monitoring and shutdown functions
- Approved flushing and shutdown procedures
An acceptable spray pattern does not prove correct ratio. Perform and document
ratio checks using the approved method before production and whenever equipment
behavior suggests a proportioning problem.
Staging Material for the Crew
Material staging connects mixing to application. The crew should receive the
correct material at the correct time without confusion, contamination, or delay.
Before a batch is mixed, confirm that:
- The application area is prepared and accepted.
- Environmental conditions are acceptable.
- Required tools, rollers, hoses, and equipment are ready.
- Details, penetrations, and termination materials are available.
- The route from mixing station to work area is clear.
- The crew can install the entire batch within its working time.
- Communication between mixer and applicators is working.
Do not mix material while the crew is still repairing the substrate, moving
equipment, or deciding where to begin.
One Batch Must Be Traceable to One Location
If a cure problem appears, the contractor must be able to identify which batch
was installed in that area and where else the same batch was used.
Assign each mixed batch a number. Record the batch number on the mixing log and
mark its installed location on a plan, grid, photograph, or area log.
Traceability can limit the amount of material that must be investigated or removed
if a component, ratio, mixing, or cure problem is discovered.
Mixing and Batch Record
Each batch record should include:
- Project name and work area
- Date and batch identification number
- Product and component names
- Manufacturer batch or lot numbers
- Quantity and mixing ratio
- Component and ambient temperatures
- Mixing start and completion times
- Mixer type, speed, and mixing duration
- Induction-complete time when applicable
- Calculated discard time
- Catalyst, filler, aggregate, or approved thinner added
- Mixer’s name or initials
- Installed location and approximate area
- Unused material and disposal method
- Observed abnormal condition or corrective action
Common Mixing and Staging Failures
-
Wrong components combined:
Similar containers or labels are confused at an uncontrolled mixing station.
-
Incorrect ratio:
Components are guessed, measured with unsuitable containers, or divided improperly.
-
Incomplete mixing:
Mixing time is shortened, the blade is unsuitable, or material along the
container sides remains unmixed.
-
Excessive air entrainment:
The mixer blade is operated above the liquid or at unnecessary speed.
-
Induction time ignored:
Application begins before the material has completed its required waiting period.
-
Expired pot life:
Material is applied after its permitted working period because it still appears liquid.
-
Oversized batch:
The crew cannot install the material before it reacts, gels, or overheats.
-
Unauthorized thinning:
Solvent is added to reduce viscosity or attempt to restore expired material.
-
Poor traceability:
The contractor cannot identify where a questionable batch was installed.
Crew Communication
The mixer and application crew must communicate continuously. The applicator
should know when a batch was mixed, when induction is complete, and when the
material must be discarded.
The mixer should know the crew’s production rate and whether an access, equipment,
weather, or substrate problem has stopped application. If production stops,
do not continue mixing batches.
Use a clear batch-number system, timers, written labels, radios when necessary,
and a single person authorized to release mixed material to the crew.
Pre-Application Checklist
- Correct approved material is at the mixing station.
- Batch numbers, expiration dates, and container condition are acceptable.
- Material temperature is within the required range.
- Mixing ratio and component quantities are confirmed.
- Mixing tools and containers are clean and appropriate.
- Required induction time and pot life are understood.
- Catalyst, filler, aggregate, or thinner instructions are available.
- Application area is prepared and accepted.
- Environmental conditions are acceptable.
- Application equipment and crew are ready.
- Batch-control forms and timers are ready.
- Spill response, waste containers, and PPE are in place.
Technical References
Use the editions identified in the contract documents and verify current
designations before incorporating standards into a proposal, submittal,
quality-control plan, or work procedure.
Key Takeaways
- Mixing is a controlled chemical and quality-control operation.
- Never guess at component ratios or catalyst quantities.
- Use complete kits unless accurate partial-kit procedures are expressly permitted.
- Material temperature and batch size directly affect working time.
- Induction time, pot life, recoat time, and chemical-service cure are different limits.
- Do not use thinning to restore material that has exceeded its pot life.
- A good spray pattern does not prove correct plural-component proportioning.
- Mix only when the substrate, equipment, and crew are ready.
- Every batch should be traceable to its installed location.
- Complete batch records protect the contractor and the finished system.
Professional responsibility:
This article provides foundational educational information and is not a substitute
for the project specification, regulatory requirements, equipment training,
or the material manufacturer’s current written instructions. Always review current
technical data sheets, safety data sheets, mixing ratios, catalyst instructions,
induction requirements, pot-life limits, plural-component equipment procedures,
ventilation requirements, and site-safety plans before beginning work.
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stored, or used in any form without prior written permission from
Azimuth Spray Systems, LLC, except for brief quotations used with
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