ASTM D7377 Water Wash-Off Resistance Testing for Traffic Paints
The water wash-off resistance of traffic paints using a water faucet can be practiced using ASTM D7377. Conventional waterborne traffic paint, is an aqueous traffic paint that uses a conventional (non-fast-dry) latex binder. This practice involves the preparation of uniform thickness films of traffic paint on standard substrates. The films are dried over different time periods and subsequently tested with the water wash-off test. The relative amount of remaining coating is determined at the end of the wash-off period.
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- Overview
- Scope, Applications, and Benefits
- Test Process
- Specifications
- Instrumentation
- Results and Deliverables
Overview
ASTM D7377 describes a standard test method for evaluating the water wash-off resistance of freshly applied traffic paints using a simulated water faucet wash-off apparatus. Freshly applied road marking paints must resist wash-off from rain or wet conditions before they have fully dried, or their retroreflective and visibility properties will be degraded or destroyed.
This test method is used by road marking paint manufacturers, transportation agencies, and pavement marking contractors to verify that traffic paint formulations meet water wash-off resistance requirements for open-to-traffic timelines.
Scope, Applications, and Benefits
Scope
ASTM D7377 applies to water-borne and solvent-borne traffic paints and evaluates:
- Resistance to water wash-off at defined times after application
- Effect of film thickness on wash-off resistance
- Comparison of paint formulations for early water resistance
- Minimum dry time before exposure to water
Applications
- Road marking paint formulation quality control
- Traffic paint specification compliance testing
- Pavement marking contractor acceptance testing
- New traffic paint product development and screening
- Hot weather and cold weather performance differentiation
Benefits
- Simulates real-world rain-on-fresh-marking conditions
- Enables rapid comparison of early water resistance across formulations
- Supports traffic management decisions on lane open times
- Simple, low-cost test reproducible in field or laboratory
- Identifies formulations at risk of premature wash-off in wet weather
Test Process
Film Application
Traffic paint is applied to a test substrate at the specified wet film thickness using a drawdown bar or applicator.
1Drying Period
The applied film is allowed to dry at controlled temperature and humidity for a specified time interval (e.g., 15 min, 30 min).
2Water Faucet Wash-Off
The coated panel is held under a flowing water stream from a faucet at defined pressure and flow rate for a specified duration.
3Assessment
The washed panel is assessed for film coverage and mass loss, reported as pass/fail or percentage coverage.
4Technical Specifications
| Parameter | Details |
|---|---|
| Standard | ASTM D7377 |
| Test Principle | Water flow wash-off of freshly applied traffic paint film |
| Applicable Materials | Water-borne and solvent-borne road marking paints |
| Water Flow Rate | As specified by method; simulates moderate rainfall |
| Dry Time Before Wash | Multiple intervals (e.g., 15 min, 30 min, 60 min) |
| Evaluation | Visual coverage rating or mass loss (%) |
Instrumentation Used for Testing
- Standard water faucet or controlled flow wash-off apparatus
- Drawdown bar or applicator for defined wet film thickness
- Wet film thickness gauge
- Analytical balance for mass before/after wash (if mass loss method used)
- Timer for drying interval and wash duration control
Results and Deliverables
- Film coverage remaining after wash (%) at each time interval
- Mass loss data (optional gravimetric method)
- Minimum acceptable dry time before water exposure
- Pass/fail comparison to specification criteria
- Comparative ranking of tested formulations
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Frequently Asked Questions
Most modern water-borne traffic paints are formulated to pass wash-off resistance at 15–30 minutes dry time at standard conditions (23°C / 50% RH); cold weather slows drying and may require longer open times.
Thicker films retain more material even if the surface is partially washed; however, proper formulation ensures adequate cohesion and water resistance at specified application rates.
ASTM D7377 is primarily designed for liquid-applied traffic paints; thermoplastic markings (applied by extrusion or spraying when molten) are characterized by different durability tests.
The faucet method uses moderate flow; for extreme rainfall simulation, modified higher-flow or impingement methods may be used, though D7377 represents the standard test condition.
Beads embedded in the paint film may slightly reduce apparent film coverage after washing due to the visual prominence of washed-out bead sites; separate film and bead retention assessments are recommended for retroreflective markings.
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