How to Use a Wet Film Thickness Gauge in Paint

By Finn McCuhil, eHow Contributor
updated: February 1, 2010

A wet film thickness gauge is the only reliable way to measure the thickness of a wet coat of paint or protective material. Assuring proper thickness and uniformity on a finish coat can prevent unpleasant surprises that might surface only after it's too late to correct them. If you are spraying a mold with gel-coat, this is particularly important since the first coat of material will wind up being your finished surface.

Difficulty: Easy
Instructions

1
Apply an initial coat of paint.
2
Hold the gauge at a 90-degree angle to the surface and press firmly. Both corners of the gauge must touch the substrate.
3
Remove the gauge and inspect the edge. The last notch with paint on the surface reflects the thickness of the paint. The number directly above the last painted notch is the thickness reading.
4
Clean the gauge with a clean rag immediately after reading. The gauge must be free of solvents, old paint or debris to give an accurate reading.

Tips & Warnings

Take all readings within 10 seconds of spraying. Paint solvent begins to evaporate as soon as it is applied. The longer you wait, the less accurate your reading.
Gauge readings will leave paint defects in paints with a high solid ratio. Painting a piece of scrap with the same surface characteristics as your project can give you a reasonably accurate reference.
The thickness gauge must be placed on a flat surface to give an accurate reading. When painting an irregular surface, turn the gauge as necessary to take your readings from a good reference point.

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