In industrial painting, the proposal usually specifies the Dry Film Thickness (DFT), as this directly determines the coating's anti-corrosion performance. However, when applicators spray on site, the paint is still wet. How can one predict the post-drying result by measuring the Wet Film Thickness (WFT)?
1. Core Formula: How to Calculate Dry Film from Wet Film? The bridge for conversion is the paint's Volume Solids.
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 diluent is added during construction (e.g., 10% diluent added), the dilution ratio must be added to the denominator.
2. Give a practical example Suppose the volume solids of a certain epoxy zinc-rich primer is 60%, and the specified dry film thickness is 60 microns:
- Calculation: 60 ÷ 60% = 100 microns.
- Operation: The construction worker only needs to pick up the wet film comb and draw it once. If the reading is around 100 microns, it indicates that the spraying amount meets the standard.
3. Manufacturer's Professional Advice
- Real-time monitoring: After each coat of spraying, immediately use a wet film comb to take samples; if any area is found to be too thin, promptly apply an additional coat.
- Consult the Technical Data Sheet (TDS): The volume solids vary for each product, so do not rely on experience to "spray blindly."