In the field of industrial coating, whether a project lasts 2 years or 20 years often comes down to a difference of just a few dozen micrometers (μm). If the coating is too thin, protection will fail; if it is too thick, it risks cracking and wastes cost. At PZSSS, we believe quality control (QC) is an inviolable bottom line. Below is the professional process for correctly performing dry film thickness (DFT) testing:
1. Difference between Wet Film Thickness (WFT) and Dry Film Thickness (DFT)
- Wet Film Thickness (WFT): Measured immediately after the paint has just been sprayed. This helps the applicator adjust the spray gun in real time to ensure the subsequent dry film meets the standard.
- Dry Film Thickness (DFT): The final thickness of the coating after it is fully cured. This is the official data for project acceptance, warranty certificates, and compliance review.
2. Professional Detection Tools
- Wet Film Comb (Comb Gauges): Used to measure WFT. The applicator presses the comb teeth vertically into the wet paint and reads the highest scale that is wetted.
- Digital Thickness Gauge: This high-precision instrument uses electromagnetic induction or eddy current principles to measure the distance from the probe to the metal substrate. To ensure accurate data, be sure to use a calibrated professional thickness gauge.
3. The "90/10 Principle" of Acceptance Professional standards (such as ISO 12944 or national standards) do not require every single point reading to be absolutely precise. The commonly accepted industry rule is:
- 90% of the measurement points must meet or exceed the specified thickness.
- The remaining 10% of measurement points shall have a thickness no less than 80% of the specified thickness. Following this principle ensures structural safety while avoiding unnecessary re-coating and 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 a coin-sized area to calculate the average.
- Repeat this process at different locations throughout the structure.
- Avoid edges, bolts, or welds as much as possible, since paint naturally builds up or thins at these locations and the readings are often not representative.
