In industrial coating applications, the specification sheet typically indicates the **Dry Film Thickness (DFT)**, as this directly determines the corrosion resistance of the coating. However, when construction workers spray on site, the paint is still wet. How can the **Wet Film Thickness (WFT)** be measured to predict the dry result? Wet film comb test, dry-wet film comparison profile, on-site quality inspection.
1. **Core Formula: How to Calculate Dry Film from Wet Film?**
The conversion bridge is the **Volume Solids** of the paint.
**Formula A: Calculate Estimated Dry Film**
Dry Film Thickness (DFT) = Wet Film Thickness (WFT) × Volume Solids %
**Formula B: Calculate Required Wet Film**
Required Wet Film Thickness (WFT) = Dry Film Thickness (DFT) ÷ Volume Solids %
Note: If a thinner is added during construction (e.g., 10% thinner), the dilution ratio must be added to the denominator.
2. **Practical Example**
Assume an epoxy zinc-rich primer has a volume solids of 60%, and the design requires a dry film thickness of 60 microns:
Calculation: 60 ÷ 60% = 100 microns.
Operation: The worker only needs to use a wet film comb to check; if the reading is around 100 microns, the spray amount meets the standard.
3. **Manufacturer’s Professional Recommendations**
– **Real-time Monitoring**: After each spray pass, immediately use a wet film comb to sample; if the film is too thin, apply a touch-up spray promptly.
– **Consult the Technical Data Sheet (TDS)**: The volume solids of each product differ; never rely on experience to “blind spray.”
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