In the industrial coating field, the difference between a project lasting 2 years or 20 years often comes down to just tens of micrometers (μm). If the coating is too thin, protection fails; if it is too thick, it risks cracking and wastes costs. At PZSSS, we believe that quality control (QC) is an unbreachable baseline. Below is the professional process for correctly conducting dry film thickness (DFT) testing:
1. Difference Between Wet Film Thickness (WFT) and Dry Film Thickness (DFT)
Wet Film Thickness (WFT): Measured immediately after paint application. This helps applicators adjust the spray gun in real time to ensure the subsequent dry film meets standards.
Dry Film Thickness (DFT): The final thickness after the coating has fully cured. This serves as formal data for project acceptance, warranty documentation, and compliance reviews.
2. Professional Testing Tools
Comb Gauges: Used to measure WFT. The applicator presses the comb teeth vertically into the wet paint and reads the highest wetted scale.
Digital Thickness Gauges: These high-precision instruments use electromagnetic induction or eddy current principles to measure the distance from the probe to the metal substrate. To ensure accurate data, always use a calibrated professional thickness gauge.
3. The “90/10 Rule” for Acceptance
Professional standards (e.g., ISO 12944 or national standards) do not require every single point reading to be absolutely precise. The industry-accepted rule is:
90% of measurement points must meet or exceed the specified thickness.
The remaining 10% of measurement points must not fall below 80% of the specified thickness.
Adhering to this principle ensures structural safety while avoiding unnecessary rework.
4. Correct Measurement Technique
Do not rely on a single reading. To obtain an accurate average:
Take at least 3 to 5 readings within an area the size of a coin.
Calculate the average.
Repeat this process at different locations across the structure.
Avoid edges, bolts, or weld seams, as paint naturally accumulates or thins in these areas, making readings unrepresentative.
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