Applying High-Build and Plural-Component Linings

High Build Does Not Mean High Tolerance for Error

High-build linings are formulated to produce greater film thickness than conventional coatings. Some are applied with heavy-duty single-component airless equipment after the material is batch mixed. Others are applied using plural-component equipment that separately meters, heats, and delivers the components to a mixer or spray gun.

These systems can improve production and reduce the number of coats required. They can also create large defective areas quickly when ratio, temperature, equipment condition, or spray technique is wrong.

Understand the Application Method

Batch-mixed airless application

Components are measured and mixed before being placed in the pump. The complete fluid section, hose, filter, gun, and tip then contain reacting material. Application, cleaning, and shutdown must be completed within the product's usable pot life.

Plural-component application

Separate components are supplied to a proportioner that meters them at the designed ratio. The components remain separate until they reach a manifold, static mixer, whip hose, or impingement-mix spray gun.

Because the mixed-material path may be short, plural-component equipment can apply products with very short reaction times. This does not remove the need to verify ratio, pressure, temperature, and complete mixing.

Hand application and touch-up

Brushes, rollers, trowels, or other approved tools may be required for stripe coating, repairs, inaccessible areas, and termination details. Touch-up material must be approved as part of the lining system.

Match the Equipment to the Material

Equipment selection should follow the material manufacturer's written recommendations. High-viscosity and high-solids products may require greater pump displacement, pressure capability, fluid passages, hose size, heating, and tip capacity than conventional coatings.

Confirm:

• Pump or proportioner type and pressure rating
• Required component ratio
• Heater and heated-hose capacity
• Transfer-pump capacity
• Fluid-hose diameter, length, and pressure rating
• Filter and screen requirements
• Manifold, static mixer, and whip-hose arrangement
• Spray-gun and mixing-chamber selection
• Tip size, fan width, and pressure rating
• Flush system and approved cleaning materials

An undersized system may produce unstable pressure, excessive material heating, restricted flow, poor atomization, and uneven film thickness.

Pre-Startup Inspection

Before material enters the equipment, inspect the entire system. Verify that components have been assembled correctly and that pressure-rated parts are suitable for the maximum working pressure.

• Check hoses for wear, cuts, bulges, leaks, and damaged fittings.
• Verify hose and accessory pressure ratings.
• Check whip restraints and coupling protection where required.
• Inspect gun guards, trigger locks, and safety devices.
• Confirm proper grounding and bonding.
• Verify heater, hose, and temperature-sensor operation.
• Confirm transfer-pump operation and material supply.
• Verify that filters, screens, mixers, and gun passages are clean.
• Confirm that flushing material will not contaminate the lining.

Condition the Material

Component temperature affects viscosity, pressure balance, atomization, mixing, and reaction speed. Both components must be conditioned within their approved ranges before startup.

Heating the hose cannot always correct material that enters the proportioner far below the required temperature. Similarly, overheated material can react too rapidly or produce excessive pressure and overspray.

Record the temperature of each component, not just the air temperature or a heater setting.

Ratio Control

A plural-component proportioner must deliver both components at the designed ratio. Ratio control depends on more than the nominal size of the pumps.

Potential causes of off-ratio delivery include:

• Empty or low material supply
• Cavitation or inadequate transfer-pump supply
• Blocked inlet screen, filter, hose, valve, or mixer
• Different component viscosities caused by temperature imbalance
• Worn pump seals, valves, or proportioning parts
• Incorrect pump or proportioner configuration
• Heater or heated-hose failure
• Pressure imbalance between components
• Leaks or unintended material bypass

Perform the ratio checks required by the equipment and coating manufacturers. Record the results before production and at the specified intervals.

Pressure Balance Is a Warning System

Stable and reasonably balanced component pressures can indicate that both sides of the system are operating normally. A sudden pressure change or persistent imbalance may indicate a restriction, temperature problem, empty container, pump problem, or off-ratio condition.

The Mixed-Material Path

Once components meet, pot life becomes critical. The mixed-material path can include a manifold, disposable mixer, whip hose, gun, and spray tip.

A long mixed-material path increases the volume of reacting material that can gel during an interruption. A path that is too short or has an unsuitable mixer may not provide complete mixing.

Use the manufacturer's approved mixer type, number of mixing elements, hose arrangement, and flushing procedure. Do not remove mixing elements to improve flow without written authorization.

Confirm the Spray Pattern Before Production

Conduct the required startup and spray-pattern checks in an approved test area. A properly operating system should produce a stable pattern without heavy edges, fingers, pulsing, excessive tailing, or obvious color streaks.

A poor pattern may result from:

• Incorrect tip size or worn tip
• Insufficient pressure
• Excessive viscosity or low material temperature
• Restricted filters, mixers, hoses, or gun passages
• Unstable pump supply
• Component pressure imbalance
• Incorrect gun distance or angle

Do not treat every pattern problem by increasing pressure. Find the cause.

Spray-Gun Technique

Hold the gun square to the surface and maintain a consistent distance, travel speed, and overlap. Arcing the gun produces heavy film in the center and thin film at the ends of each pass.

Trigger the gun at the correct point and use a planned spray sequence. Each pass should overlap the previous pass sufficiently to produce uniform coverage without excessive buildup.

On large surfaces, use reference points or controlled work sections. Random spraying makes it difficult to track thickness, overlaps, and missed areas.

Cross-Passing and Multiple Passes

Some high-build systems require multiple spray passes to achieve the specified thickness. Passes may be applied in different directions to improve uniformity, but the sequence must follow the manufacturer's requirements.

Avoid excessive buildup at pass intersections, corners, welds, and termination points. Heavy localized film can sag, crack, trap solvent, generate heat, or cure differently from surrounding material.

Controlling Wet-Film Thickness

Wet-film measurements provide immediate feedback while the applicator can still adjust technique. The required wet-film thickness depends on the specified dry-film thickness, product solids, thinning, and application behavior.

A wet-film gauge can help identify:

• Thin passes
• Excessive film build
• Uneven coverage
• Changes caused by tip wear
• Changes in applicator speed or distance

Notched gauges provide approximate readings and may be difficult to interpret on very rough, rapidly curing, reinforced, or textured systems. Use the method approved for the product and substrate.

Film Thickness Is a Range

More lining is not automatically better. The project specification and manufacturer normally establish minimum and maximum thickness requirements.

Edges, Welds, Corners, and Penetrations

Spray application naturally produces different film build around sharp edges, welds, bolts, corners, nozzles, penetrations, and other irregular shapes. These areas may require stripe coating, special spray passes, filling, or reinforcement.

Avoid flooding corners in an attempt to correct poor surface geometry. Fabrication defects, sharp edges, rough welds, and voids must be corrected before lining application.

Article 17 addresses difficult areas and stripe coating in detail.

Concrete Outgassing

Concrete can release air or moisture vapor into freshly applied lining, producing bubbles and pinholes. Watch the surface immediately after application, particularly while the concrete temperature is rising.

Approved control measures may include:

• Applying during stable or falling substrate temperature
• Using a compatible pore-filling primer
• Filling bugholes and voids before application
• Using an approved grout or scratch coat
• Applying a controlled initial pass

Spraying additional material over active bubbles may hide rather than eliminate the defect.

Recognizing Off-Ratio Material

Off-ratio material may appear:

• Soft, gummy, sticky, or greasy
• Unusually brittle or hard
• Streaked or uneven in color
• Foamed, bubbled, or porous
• Different in texture or gloss
• Slow to cure or apparently uncured

Fast-set material may appear hard even when it did not mix correctly. Visual appearance alone cannot always confirm acceptable cure or ratio.

Production Tracking

Track where the applicator was working while each material batch or equipment condition was active. This allows a problem to be isolated if inspection later identifies questionable cure, ratio, temperature, or thickness.

Record:

• Product and component batch numbers
• Application start and stop times
• Work area or grid location
• Material and hose temperatures
• Component pressures
• Ratio-check results
• Tip or mixing-chamber identification
• Wet-film readings
• Interruptions, alarms, and corrective actions

Planned Interruptions and Shutdown

Before application begins, the crew should understand how long mixed material can remain in the manifold, mixer, whip hose, gun, or batch equipment.

Establish procedures for:

• Brief spray interruptions
• Tip or gun cleaning
• Changing a static mixer
• Refilling component supplies
• Responding to pressure or temperature alarms
• End-of-shift shutdown
• Emergency shutdown
• Flushing and waste collection

A delayed flush can leave cured material inside expensive equipment. An unnecessary flush can introduce incompatible solvent into the lining. Follow the approved sequence.

High-Pressure Injection Hazard

Airless and plural-component equipment can produce pressures capable of injecting coating through the skin. The injury may appear small but can cause severe internal damage and require immediate specialized medical treatment.

• Never point the gun at any person or body part.
• Never place a hand or finger over the spray tip.
• Never attempt to stop a leak with a hand, glove, or rag.
• Use the trigger lock and tip guard.
• Follow the complete pressure-relief procedure before servicing equipment.
• Replace damaged hoses and fittings rather than attempting temporary repairs.
• Seek immediate emergency medical treatment for suspected injection injury.
• Provide medical personnel with the material safety information.

Ventilation and Chemical Exposure

High-build materials may contain solvents, amines, isocyanates, styrene, or other hazardous components. Spray application creates aerosol as well as vapor.

Use engineered ventilation, exposure controls, respiratory protection, protective clothing, gloves, eye protection, and confined-space procedures based on the product and hazard assessment.

Nearby workers must also be protected from vapor and overspray. Ventilation required for worker safety must remain in operation for the required period during application and cure.

When Application Should Stop

Contractor Field Checklist

Knowledge Check

Key Takeaway