The primary purpose of measuring wet film thickness (WFT) is to ensure that the correct amount of liquid coating is applied to a surface at the time of application, confirming it aligns with the calculated target thickness before significant solvent evaporation occurs.
Wet film thickness, or WFT, is defined as the measured thickness of any applied wet paint that is liquid-based. It represents the thickness of the coating before it dries or cures and any solvents evaporate.
Measuring WFT serves a crucial role in the coating process. According to the reference provided, a wet film thickness gage should be used by the applicator as the coating is being applied. This timing is critical to ensure that the measurement is representative of the calculated wet film before significant solvent evaporation occurs. As solvents evaporate from the wet coating, the film thickness naturally decreases, resulting in the final dry film thickness (DFT). By measuring WFT early, applicators can verify they have applied the intended amount of material needed to achieve the specified final dry thickness.
Why Measure Wet Film Thickness?
Measuring WFT offers several important benefits during the application of liquid coatings:
- Quality Control: It provides an immediate check on the applicator's technique and ensures the coating is applied within the specified thickness range while still in its liquid state.
- Predicting Dry Film Thickness (DFT): WFT measurement is directly related to the final DFT. Knowing the percentage of solids in the coating allows applicators to calculate the expected DFT from a given WFT measurement. This is essential for achieving the required protective properties and performance of the coating system.
- Material Consumption: By verifying the WFT, applicators can ensure the correct amount of material is being used per unit area, helping manage costs and avoid over-application or under-application.
- Avoiding Defects: Applying the wrong WFT can lead to various coating defects, such as sagging (if too thick) or insufficient coverage and premature failure (if too thin). Measuring WFT helps prevent these issues.
How WFT Measurement Works
A wet film thickness gauge, such as a comb gauge or wheel gauge, is used to measure WFT. The gauge is placed onto the freshly applied wet coating, and the reading indicates the thickness. As noted in the reference, this measurement must be taken promptly as the coating is being applied.
The Critical Timing of WFT Measurement
The emphasis on measuring WFT before significant solvent evaporation occurs highlights the importance of speed. The thickness of the wet film is dynamic and will change as soon as evaporation begins. An accurate WFT measurement provides a snapshot of the thickness at the moment of application, which is the basis for calculating the final dry film thickness and ensuring the job meets specifications.
By controlling WFT, applicators have the best opportunity to achieve the desired dry film thickness and ensure the long-term performance and durability of the coating.
| Measurement Type | Timing | Purpose |
|---|---|---|
| Wet Film Thickness (WFT) | During application | Verify applied liquid thickness; Predict DFT |
| Dry Film Thickness (DFT) | After curing/drying | Verify final solid coating thickness |
