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Portable Plural-Component Coating Systems for Contractors

Article 17 of 24

Calibration, Ratio Verification, Output Testing, and Records

A plural-component proportioner can display normal pressures, maintain heat, and produce an acceptable spray pattern while still delivering the wrong material ratio. Calibration, ratio verification, and output testing provide measurable evidence that the system is delivering the coating as specified. Complete records connect that evidence to the material, equipment, crew, time, and area of application.

Four Different Quality-Control Activities

These terms are related, but they are not interchangeable.

Important: Similar component pressures do not prove correct proportioning. Pressure indicates resistance to flow. It does not directly measure the quantity of each component being delivered.

Establish the Acceptance Requirements Before Testing

The contractor should not invent a universal ratio tolerance. Acceptable variation depends on the coating formulation, proportioning equipment, test method, manufacturer instructions, and project specification.

Establish the following before work begins:

• The specified mix ratio.
• Whether the ratio is stated by volume or by weight.
• The approved ratio-verification procedure.
• The permitted ratio tolerance.
• The required number of test repetitions.
• Required operating temperatures, pressures, and flow conditions.
• Test frequency and required witnesses.
• The response required when a test fails.

Follow the coating manufacturer’s written requirements, the proportioner manufacturer’s procedure, the project specification, and the approved contractor quality-control plan. When those requirements conflict, obtain written clarification before application.

Volume Ratio and Weight Ratio Are Not the Same

A coating specified at 4:1 by volume is not necessarily 4:1 by weight. Component A and Component B may have different densities. A weight-based check of a volume-based ratio requires the verified density of each component.

ASTM D1475 provides a recognized method for determining the density of liquid coatings and related products. Use current product data or properly measured density values. Density changes with temperature, so test conditions and manufacturer instructions matter.

Example: 4:1 by Volume

A 4:1 system contains five total ratio parts:

• Component A should represent 4/5, or 80 percent, of the combined volume.
• Component B should represent 1/5, or 20 percent, of the combined volume.

If the test collects 2,000 milliliters in total, the theoretical quantities are 1,600 milliliters of A and 400 milliliters of B. Whether those results are acceptable depends on the authorized tolerance—not simply on whether the numbers appear close.

Preparing for a Ratio Test

1. Confirm the materials. Record the manufacturer, product, component designations, batch or lot numbers, and expiration information.
2. Confirm the ratio basis. Determine whether the specified ratio is by volume or weight.
3. Confirm the equipment configuration. Record the proportioner, pump sizes, meters, software recipe, mix manifold, hose arrangement, and sampling-valve configuration.
4. Inspect the system. Check supply levels, strainers, valves, seals, hoses, connections, heaters, sensors, grounding, and alarms.
5. Condition the materials. Bring components to the manufacturer’s required temperature and agitation condition.
6. Prime completely. Remove air, flushing solvent, storage fluid, and previous material from the component circuits.
7. Stabilize operation. Allow circulation, pressure, and temperature to stabilize before collecting samples.
8. Prepare test equipment. Use clean, compatible containers and a suitable scale or graduated vessels. Identify A and B containers clearly.
9. Document the instruments. Record scale, vessel, timer, temperature instrument, and calibration or verification status when required.

Some equipment manufacturers recommend containers with graduations no greater than five percent of the quantity being measured. When accurate weight measurements and reliable component densities are available, weighing may provide better resolution than reading coarse container graduations.

Conducting the Ratio Verification

The exact sequence must come from the proportioner manufacturer and the approved project procedure. A general field sequence includes the following:

1. Wear the required personal protective equipment and control the test area.
2. Use approved pressure-relief and sampling procedures.
3. Ground and bond equipment and conductive containers when required.
4. Tare each labeled container or record its empty weight.
5. Place separate containers at the Component A and Component B sampling outlets.
6. Initiate the equipment’s ratio-test or batch-dispense function, or follow the authorized manual test procedure.
7. Collect both components for the required amount, number of cycles, or time.
8. Measure the net volume or net weight of each component.
9. Calculate the delivered ratio using the correct basis.
10. Compare the result with the authorized acceptance range.
11. Repeat the test when required to establish repeatability.
12. Record the raw measurements, calculations, result, and acceptance decision.

Test Under Representative Operating Conditions

A proportioner may pass a low-output test but drift when operated at the flow needed for production. Ratio performance can be affected by:

• Component temperature and viscosity
• Feed-pump condition and inlet pressure
• Blocked or partially restricted strainers
• Pump speed and changeover performance
• Discharge pressure and downstream restriction
• Hose length, diameter, and temperature
• Meter condition, valve timing, and controller settings
• Worn seals, check valves, cylinders, or pump components

Where the approved procedure permits, verify performance at conditions representative of production. Record the conditions so the test can be repeated and meaningfully compared with later results.

Output Testing

Output testing determines whether the proportioner can support the planned application rate while remaining inside its stable operating range.

For example, if the system delivers 2.5 gallons during a 30-second controlled test:

2.5 gallons ÷ 0.5 minute = 5 gallons per minute

An output record should state:

• Whether mixed material or separate components were collected
• Collection time or number of pump cycles
• Material temperatures
• Feed and discharge pressures
• Tip or restriction used during testing
• Measured quantity and calculated output

A high theoretical output rating does not guarantee usable jobsite output. Material viscosity, hose configuration, temperature, pressure, elevation, tip size, and equipment condition all affect actual delivery.

When Ratio Verification Should Be Performed

Test frequency must follow the governing documents. Common verification points include:

• Initial equipment commissioning
• Before beginning a project, shift, or production period
• After changing the product, ratio recipe, pump size, meter, or system configuration
• After maintenance, repair, or calibration
• After loss of prime, cavitation, an off-ratio alarm, or an unexplained pressure imbalance
• After changing material lots when required by the specification or quality plan
• When abnormal cure, color, hardness, spray pattern, or coating performance is observed
• At the interval required by the equipment manufacturer, coating manufacturer, or project specification

Responding to a Failed Test

An unacceptable ratio test is a stop-work condition until the cause is identified, corrected, and successfully retested.

1. Stop application. Do not continue spraying while assuming the condition will correct itself.
2. Identify the affected work. Establish the time and location of the last acceptable verification and the first known failure.
3. Quarantine suspect work. Prevent overcoating, turnover, or concealment until disposition is authorized.
4. Inspect the material supply. Check component levels, agitation, temperature, contamination, feed pumps, inlet restrictions, and air entry.
5. Inspect the proportioner. Check calibration values, pump operation, meters, valves, filters, seals, sensors, alarms, and software settings.
6. Correct the cause. Perform only authorized adjustments and repairs.
7. Retest. Do not resume production until the required tests pass.
8. Obtain disposition. Follow written direction for evaluating, repairing, removing, or accepting suspect coating.
9. Document everything. Record the failure, affected area, investigation, corrective action, retest, and authorization to resume.

A coating that looks normal immediately after application may still be off ratio. Final cure, adhesion, chemical resistance, hardness, flexibility, and long-term performance can be affected.

Ratio and Output Test Record

A useful record should contain enough information for another qualified person to understand what was tested and reproduce the evaluation.

Preserve the Original Data

Do not rewrite test results to make a record appear cleaner. Preserve the original readings and calculations. Correct paper records with a single line through the incorrect entry, then add the correct information, date, and initials. Electronic records should retain controlled revision history when the system permits.

Accurate records protect the owner, coating manufacturer, equipment supplier, inspector, contractor, and applicator. They can also reveal developing equipment problems before those problems become coating failures.

Technical References and Further Study

• Graco XM Plural-Component Sprayers—Operation Manual — Includes equipment-specific batch-dispense and ratio-test procedures. Use the manual that matches the exact equipment model and configuration.
• WAGNER TwinControl Operating Manual — Manufacturer procedures addressing calibration, operation, monitoring, batch functions, and equipment checks.
• ASTM D1475—Standard Test Method for Density of Liquid Coatings, Inks, and Related Products — A recognized method for determining liquid-coating density when density is required for quality control or weight-to-volume calculations.
• Sames Ratio-Test Equipment Information — An example of manufacturer-provided equipment intended to support ratio verification.
• Current coating manufacturer product data sheets, application instructions, safety data sheets, plural-component setup procedures, and project-specific quality-control requirements.

Manufacturer references are provided as technical examples and educational resources. Their inclusion does not constitute a product endorsement. Always obtain the current manual for the exact equipment and software version being used.

Professional Responsibility

Plural-component coatings may contain hazardous, reactive, flammable, sensitizing, or high-temperature materials. Follow the coating and equipment manufacturers’ current written instructions, safety data sheets, pressure-relief procedures, grounding and bonding requirements, ventilation requirements, personal-protective-equipment requirements, project specifications, and applicable regulations. Calibration and testing must be performed only by trained and authorized personnel.

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