Knowledge Base
Coating Film Thickness Measurement
Coating Film Thickness Measurement
Coating film thickness measurement is the process of determining how thick an applied coating is, either while it is still wet or once it has cured. It is a core quality control check in the paints and coatings industry, used to confirm a coating meets its specification for protection, appearance, and cost control. The governing standard for dry film measurement is ISO 2808.
How to Measure Wet and Dry Coating Film Thickness
There are three measurement stages. Wet film thickness (WFT) is checked immediately after application using a comb or wheel gauge. Dry film thickness (DFT) is measured after curing, using magnetic induction on steel, eddy current on non-ferrous metals, or ultrasonic methods on non-metals. Contactless measurement covers both wet and cured coatings without touching the surface.
Measuring film thickness helps you protect the integrity of your product and brand: too thin and the coating underperforms; too thick and you waste material and risk defects. For a full walkthrough of methods and instruments, read our Test Method Explainer below.
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TQC Sheen Wet Film Thickness Gauges
Our handy wet film thickness gauges accurately measure a coating’s thickness immediately after it’s been applied to a substrate.
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Pick up a set of plastic wet film combs from TQC Sheen for consistently accurate film thickness measurements of wet paints and coatings.
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Roll a stainless steel wheel across your freshly applied coating to read wet film thickness on large, curved or coil-coated surfaces with the TQC Sheen Wet Film Thickness Wheels. Four range options from 0-100 μm through 0-1000 μm, better than 3 μm accuracy. Dispatched within 2 days.
FAQs
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Wet film thickness (WFT) is measured immediately after application, while the coating is still wet. Dry film thickness (DFT) is measured after the coating has cured. DFT is always lower than WFT, because solvents evaporate as the coating dries. The difference depends on the coating’s volume solids content.
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Multiply the wet film thickness by the coating’s volume solids percentage, divided by 100: DFT = WFT x (volume solids % / 100). For example, a 100 micron wet film of a 50 percent solids coating gives roughly 50 microns dry film. Check the coating supplier’s data sheet for exact volume solids.
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Both measure wet film thickness. A comb gauge is quick, low-cost, and ideal for flat surfaces and spot checks. A wheel gauge rolls across the surface and suits wet lacquers, paints, and coil-coated surfaces where a rolling action gives a cleaner reading. Choose based on surface type and how many readings you take.
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Both are non-destructive dry film methods. Magnetic induction measures non-magnetic coatings on ferrous substrates such as steel and iron. Eddy current measures non-conductive coatings on non-ferrous metals such as aluminum, copper, and brass. Many gauges combine both and detect the substrate automatically.
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Yes. Non-metallic substrates need ultrasonic measurement rather than magnetic or eddy current methods. An ultrasonic gauge sends a pulse through the coating and measures the echo, giving non-destructive readings on wood, concrete, plastic, composites, and fiberglass, including multi-layer systems.
Related Articles
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Coating Film Thickness Measurement Explained: Wet Film, Dry Film, and Contactless Methods (ISO 2808)
Why film thickness is a critical quality control parameter Film thickness is one of the most important quality checks for any applied coating. Get it wrong in either direction and the coating fails to do its job. Too thin, and it will not provide the protection, appearance, or function the specification calls for. Too thick,…
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Key terms Term Definition Wet film thickness (WFT) Coating thickness measured immediately after application, before drying or curing. Dry film thickness (DFT) Coating thickness measured after the coating has cured. Volume solids The percentage of a coating that remains on the surface after solvents evaporate. Magnetic induction DFT method for non-magnetic coatings on ferrous (steel,…
