AirSprayTech Academy Certificate Program
Secondary Containment Coating Systems for Industrial Contractors
Article 17 of 24
Application Methods and Equipment
The correct containment material can still fail when applied with the wrong
equipment or technique. Brush, roller, squeegee, trowel, airless spray, and
plural-component spray each serve a purpose—and each requires its own controls.
Learning Objectives
After completing this article, you should be able to:
- Compare common containment-lining application methods.
- Match equipment to material viscosity, film build, reaction rate, and project geometry.
- Recognize the strengths and limitations of brush, roller, squeegee, trowel, and spray application.
- Identify critical controls for airless and plural-component equipment.
- Understand how spray technique affects coverage, thickness, continuity, and overspray.
- Establish equipment inspections and field checks before production begins.
The Material Determines the Equipment
Containment products range from low-viscosity penetrating primers to filled mortars,
reinforced laminates, high-build epoxies, catalyzed vinyl esters, and fast-reacting
polyurea membranes. One pump, roller cover, spray tip, or trowel cannot properly
apply all of them.
Equipment selection should consider:
- Material viscosity and solids content
- Aggregate, fiber, or flake content
- Required wet- and dry-film thickness
- Pot life, gel time, and reaction speed
- Component ratio and mixing requirements
- Substrate texture and porosity
- Open-area production and detail work
- Access, hose length, elevation, and containment geometry
- Ventilation, overspray, and ignition-control requirements
The coating manufacturer’s current application instructions should identify
approved methods, equipment ranges, tip or nozzle guidance, thinning limitations,
and special processing requirements.
Do Not Force the Material through Unsuitable Equipment
When equipment cannot move or atomize a material properly, the answer is not
automatically more pressure or more thinner. Excessive pressure increases wear,
overspray, injection hazard, heat, and equipment stress. Unauthorized thinning
can reduce film build, change cure, promote solvent retention, and weaken chemical resistance.
Use equipment with adequate pressure, volume, fluid-passage size, temperature
control, and wetted-part compatibility for the material. If the system cannot
deliver the product correctly, change the equipment—not the coating formulation.
Brush Application
Brushes are valuable for stripe coating, small repairs, edges, welds, pits,
penetrations, bolts, corners, coves, and areas that cannot be reached properly
with production equipment.
Brushing can work material into irregularities and improve wetting at difficult
details. It also gives the applicator direct control over placement.
Limitations include slow production, visible brush marks, variable thickness,
possible air entrainment, and difficulty applying high-build material uniformly.
Brush type and bristle material must be compatible with the resin and solvent.
A brush that sheds bristles or softens in the coating can contaminate the lining.
Roller Application
Rollers are commonly used for primers, thin- and medium-build coatings, backrolling,
aggregate-seeded layers, and some topcoats. Roller application can provide good
control on floors and walls without spray overspray.
Roller-cover material, nap length, core construction, width, and solvent resistance
should match the coating and surface texture. A roller that is too short may bridge
over surface depressions. One that is too long can introduce excess texture and air.
Do not stretch material beyond its intended coverage. A roller can continue moving
long after it has stopped depositing the required film thickness.
Use a consistent loading, placement, and finishing pattern. Overworking material
as it begins to cure can create texture, roller marks, entrained air, color variation,
or loss of continuity.
Backrolling
Backrolling follows the initial placement of material by spray, squeegee,
or another method. It may be used to work primer into porous concrete, distribute
material, release air, improve appearance, or create a uniform texture.
Backrolling should occur while the material remains within its workable stage.
Waiting too long can lift, drag, or texture the coating. Excessive backrolling can
remove material from high areas and deposit it in low areas.
The applicator and backroller must maintain close spacing and communication.
The spray operator should not advance so far that the backroller cannot work the
material before it begins to cure.
Squeegee Application
Notched or flat squeegees are commonly used to place self-leveling resins,
slurries, membranes, and high-build materials over horizontal surfaces.
The squeegee distributes a measured quantity rapidly before rolling or finishing.
Notch shape and size influence the amount of material placed, but actual thickness
also depends on squeegee angle, pressure, wear, substrate texture, viscosity,
temperature, and applicator technique.
Squeegee notches should be checked during the shift. Worn notches place less material.
Replace the tool before wear creates an unacceptable reduction in film thickness.
Trowel Application
Trowels are used for resin mortars, coves, patches, sloping materials, heavy-duty
surfacings, and filled chemical-resistant systems. Trowel application can build
substantial thickness and correct controlled surface irregularities.
The crew must maintain the specified resin-to-aggregate relationship. Adding
unapproved aggregate to make the material easier to trowel can create a dry,
porous, or poorly bonded system.
Compact the mortar sufficiently to eliminate voids while maintaining the required
thickness and slope. Avoid overworking material after it begins to react.
Trowel marks, low spots, ridges, porous areas, and cold joints should be corrected
before the succeeding seal coat or lining layer is applied.
Single-Component Airless Spray
Single-component airless equipment can apply many primers, epoxies, novolacs,
vinyl esters, and other high-performance linings after their components have been
batch mixed.
The pump must provide enough volume and pressure to move the material through the
selected hose, gun, filter arrangement, and spray tip. The pump ratio by itself
does not establish actual operating pressure or production capacity.
Important equipment considerations include:
- Pump pressure capability and output
- Fluid-section and seal compatibility
- Hose diameter and total hose length
- Gun pressure rating and fluid-passage size
- Spray-tip orifice and fan width
- Filter or screen size permitted for the material
- Material temperature and viscosity
- Flushing materials and cleanup time
Remove or change filters only when permitted by the coating and equipment manufacturers.
Filled, flake-reinforced, or fiber-containing products may plug fine screens.
Use the Lowest Pressure That Produces a Proper Pattern
Increase airless pressure only until the spray pattern is properly atomized and
free of unacceptable tails. Continuing to increase pressure after obtaining a
suitable pattern increases overspray, tip wear, pump wear, hose stress, and
injection hazard without improving the finished film.
If adequate atomization cannot be achieved within safe equipment limits, check
material temperature, viscosity, tip selection, filters, restrictions, hose size,
and pump capacity before considering any permitted thinning.
Spray-Tip Selection
Spray-tip selection affects material flow, fan width, atomization, production,
and thickness. The orifice must be large enough for the material while remaining
within the pump’s capacity.
A wide fan can increase production on open surfaces but may be difficult to control
around curbs, walls, penetrations, or narrow areas. A narrow fan improves control
but can produce excessive film build if travel speed is not adjusted.
Tips wear during use. As the orifice enlarges, output rises and the fan can become
narrower. A worn tip changes the application rate even when the pressure setting
has not changed.
High-Pressure Injection Is a Medical Emergency
Airless and plural-component equipment can inject coating into the body through
a small opening that may initially appear minor. The injury can cause severe tissue
damage and may require immediate specialized treatment.
Never place a hand near a spray tip, point the gun toward a person, or attempt to
stop a leak with a glove or rag. Engage the trigger lock and completely relieve
pressure before servicing equipment.
Any suspected injection injury requires immediate emergency medical attention.
Provide medical personnel with the product safety data sheet and identify the
material involved.
Plural-Component Spray
Plural-component equipment is used when the material reacts too quickly for
conventional batch mixing or when heating and separate component delivery are
needed for proper application.
The equipment may combine components at a mix manifold, through a static mixer,
or within an impingement-mix spray gun. The correct arrangement depends on the
material and equipment design.
Critical operating controls include:
- Accurate component ratio
- Balanced material supply
- Required component temperatures
- Stable operating pressures
- Correct hose temperatures
- Proper gun and mixing configuration
- Ratio alarms or shutdown controls
- Documented ratio verification
- Correct shutdown and flushing procedures
The operator must understand both the coating and proportioner. Plural-component
application should not be assigned to personnel who have only operated ordinary
single-component airless equipment.
Spray Technique
The spray gun should normally be held perpendicular to the surface at a consistent
distance. Arcing the gun changes the distance across the pass and deposits less
material at the edges.
Begin moving before triggering and release the trigger before stopping. Maintain
a consistent travel speed and overlap each pass according to the spray pattern
and application procedure.
Crosshatching—applying one series of passes in one direction and another series
perpendicular to it—may help achieve uniform coverage when allowed by the material’s
working and recoat characteristics.
The applicator should adjust position to maintain the correct angle rather than
turning the wrist or spraying at a severe angle. Difficult details may require
a smaller fan, brush, roller, stripe coat, or separate application sequence.
Edges, Corners, and Shadowed Areas
Spray patterns do not wrap evenly around edges, behind pipes, beneath equipment,
or into sharp inside corners. These locations may receive much less coating than
the surrounding open surface.
Use stripe coats, detail coats, adjusted gun angles, smaller spray patterns,
brushes, or rollers as specified. Inspect from multiple directions with strong lighting.
Do not attempt to correct every thin detail by slowing the production pass.
This often creates excessive buildup on adjacent areas while still leaving the
hidden surface insufficiently coated.
Wet-Film Thickness
Wet-film measurements give the applicator immediate information while correction
is still practical. For many coatings, expected dry-film thickness can be estimated
from wet-film thickness and the product’s volume-solids content.
The calculation must account for any manufacturer-approved thinner added.
Surface profile, roughness, porosity, overspray, application loss, and material
remaining in equipment are not fully represented by a simple theoretical calculation.
Wet-film gauges may be unsuitable for materials that gel almost immediately,
contain large aggregate, or are applied over very rough surfaces. Use the inspection
method approved for the system.
Measurements should be distributed across the work and include areas where gun
distance, access, geometry, or application rate changes.
Material Usage as a Production Check
Compare the amount of material used with the actual area completed. This does not
replace thickness measurement, but it can identify a developing problem.
Low material usage may indicate thin application, excessive spreading, skipped
areas, inaccurate area measurement, or unauthorized thinning. High usage may
indicate excessive thickness, overspray, leakage, waste, rough surfaces, porous
concrete, or material left in equipment.
Track usage by work area and shift instead of waiting until the entire project is
complete. Early detection allows the crew to correct application before large
areas must be repaired.
Equipment Inspection before Production
- Pump, motor, engine, or air supply is suitable for the work.
- All equipment pressure ratings meet or exceed operating pressure.
- Hoses are correctly rated, undamaged, and electrically grounded where required.
- Couplings, guards, whip checks, and safety devices are installed.
- Gun trigger lock and tip guard function correctly.
- Fluid passages, filters, and screens match the material.
- Spray tip or nozzle is correct and not excessively worn.
- Heaters and temperature controls operate correctly.
- Plural-component pressures and ratio controls are verified.
- Flush materials and waste containers are ready.
- Grounding, ventilation, lighting, and ignition controls are in place.
- Required PPE and emergency procedures are available.
Test Application
Before production begins, perform a controlled test application on an approved
area or representative test panel. Confirm equipment settings, spray pattern,
application rate, coverage, texture, thickness, curing behavior, and crew coordination.
The test should include representative horizontal, vertical, and detail surfaces
when practical. A setup that works on an open floor may not work on walls,
coves, penetrations, or overhead locations.
Record the accepted equipment configuration and settings. The test result becomes
the field reference for production, although adjustments may still be necessary
as material temperature, tip wear, or conditions change.
Common Application Defects
-
Thin film:
Excessive spreading, fast travel, insufficient output, worn tools,
or inadequate overlap.
-
Runs and sags:
Excessive film build, slow travel, incorrect temperature,
overthinning, or unsuitable application method.
-
Dry spray:
Excessive pressure, excessive gun distance, poor atomization,
high airflow, or material gelling before reaching the surface.
-
Pinholes and bubbles:
Concrete outgassing, entrained air, porosity, moisture,
poor priming, or excessive rolling.
-
Roller or brush marks:
Incorrect tool, uneven loading, material overworking,
or application after cure has advanced.
-
Uneven texture:
Inconsistent squeegee angle, roller pressure, spray distance,
tip wear, viscosity, or working time.
-
Missed or shadowed areas:
Poor access, inadequate lighting, unsuitable fan width,
or failure to detail before production application.
-
Off-ratio material:
Plural-component proportioning, supply, temperature,
pressure, or mixing failure.
Field Quality-Control Checklist
- Application method is approved for the specific material.
- Equipment capacity and pressure ratings are suitable.
- Wetted parts, hoses, filters, tips, and tools are compatible.
- Equipment has been inspected and safety devices are functioning.
- Plural-component ratio and temperature controls are verified.
- Test application and spray pattern are acceptable.
- Gun distance, angle, speed, and overlap are consistent.
- Stripe coats and detail work are completed as specified.
- Wet-film thickness is checked when applicable.
- Material usage agrees reasonably with area and specified thickness.
- Tools, tips, and squeegee notches are monitored for wear.
- No thin areas, runs, sags, dry spray, bubbles, or missed locations remain.
- Equipment settings and quality-control results are documented.
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 application procedure.
Key Takeaways
- Match the application method and equipment to the specific material.
- Do not use excessive pressure or unauthorized thinner to overcome unsuitable equipment.
- Brushes and rollers remain important for stripe coats and difficult details.
- Squeegee and trowel application require controlled tool angle, wear, and material usage.
- Airless equipment must provide both adequate pressure and adequate volume.
- Plural-component equipment must accurately heat, meter, mix, and deliver both components.
- A proper spray pattern does not prove correct ratio or film thickness.
- Wet-film checks and material usage help crews control thickness during application.
- Edges, corners, penetrations, and shadowed areas require separate attention.
- High-pressure injection injuries require immediate emergency medical care.
Professional responsibility:
This article provides foundational educational information and is not a substitute
for the project specification, regulatory requirements, equipment training,
or the coating and equipment manufacturers’ current written instructions.
Always review current technical data sheets, safety data sheets, equipment manuals,
pressure ratings, grounding requirements, ventilation requirements, application
procedures, and site-safety plans before beginning work.
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Azimuth Spray Systems, LLC, except for brief quotations used with
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