Poor adhesion or film peeling in water-based paints during application is often caused by material issues, application techniques, or environmental factors. The following are common causes and their corresponding solutions:

I. Improper Substrate Preparation (Primary Cause)
1. Causes:
a. Substrate surface has oil, grease, dust, moisture, or mold release agent residue.
b. Substrate is too smooth (e.g., metal, plastic, glass) and has not been sanded or roughened.
c. Wood has excessive moisture content (>12%) or contains resin/wax.
d. Old coating was not properly removed, leading to poor intercoat adhesion.
2. Solutions:
a. Cleaning: Thoroughly remove oil and dust using solvents (e.g., alcohol, acetone) or dedicated cleaners.
b. Abrasion: Sand the substrate surface with sandpaper (recommended 180-240 grit) to increase roughness. Metal/plastic can be sandblasted or phosphated.
c. Drying: Dry wood to a moisture content <12% to prevent subsequent film peeling caused by moisture evaporation.
d. Sealing: Apply a sealing primer on porous substrates (e.g., wood, plaster) to prevent moisture penetration.
II. Coating-Related Issues
1. Causes:
a. Poor quality paint (low resin content, improper formulation).
b. Paint is expired or stored improperly (e.g., frozen, high temperature), leading to degraded performance.
c. Over-dilution, resulting in low viscosity and poor film formation.
d. Primer and topcoat are incompatible (e.g., using a water-based topcoat over an oil-based primer).
2. Solutions:
a. Select water-based paints from reputable brands, ensuring adhesion metrics are qualified.
b. Dilution Control: Dilute according to manufacturer’s instructions; avoid excess water (generally not exceeding 10%).
c. Viscosity Adjustment: Use a viscometer to check and adjust viscosity to the required range for application (typically 20-30 seconds, Zahn cup #4).
d. Compatibility Test: Ensure primer and topcoat are both water-based systems. Perform a small test application beforehand if necessary.
III. Application Environment Issues
1. Causes:
a. Temperature too low (<5°C): Difficult film formation and slow drying for water-based paints.
b. Humidity too high (>80%): Slow water evaporation, causing blushing or tackiness.
c. Poor ventilation: Affects film curing, leading to reduced adhesion.
2. Solutions:
a. Temperature/Humidity Control: Maintain ambient temperature between 10-35°C and humidity between 40-70%.
b. Auxiliary Equipment: Use dehumidifiers, heaters, or infrared lamps to accelerate drying.
c. Avoid application in low temp/high humidity: Preheat substrates in winter or use low-temperature formulated water-based paints.
IV. Application Technique Issues
1. Causes:
a. Excessive coat thickness: Differing drying rates between inner and outer layers creates shrinkage stress.
b. Improper intercoat drying time: Undercoat not fully dry, or interval too long (exceeding the recoat window).
c. Incorrect application method: Improper spray gun distance or pressure leads to uneven film.
2. Solutions:
a. Thin Coats, Multiple Layers: Recommended wet film thickness per coat is 80-120 μm.
b. Control Intercoat Time: Follow data sheet for recoat times (typically touch dry in 30 mins, hard dry in 2-4 hours).
c. Standardized Operation:Spray gun distance 20-30 cm, air pressure 0.3-0.5 MPa.
i. Use even pressure when rolling; avoid misses or buildup.
V. Other Factors
1. Substrate/Paint Incompatibility:Special substrates (e.g., PP plastic, galvanized metal) require dedicated water-based primers.
2. Curing Agent Issues:For two-component water-based paints, mix strictly according to the ratio and use within the pot life.
3. Mechanical Damage:Avoid friction or impact on the film before it is fully cured.
Summary Troubleshooting Steps
1. Inspect Substrate: Cleanliness, roughness, moisture content.
2. Verify Coating: Expiry date, dilution ratio, compatibility.
3. Optimize Environment: Temperature, humidity, ventilation.
4. Standardize Application: Film thickness, intercoat time, tool operation.
5. Test Sample: Perform a test application in an inconspicuous area before full-scale work; proceed only if results are satisfactory.
Through systematic troubleshooting and adjustment, the adhesion of water-based paints can be significantly improved, preventing film peeling issues.