Measuring paint thickness on various surfaces has evolved over the years. The primitive pen-like devices have disappeared, in favor of magnetic pull-off and electronic gauges that measure in microns. Gauges today come in compact hand-held designs, tabulate very accurate and consistent measurements, and some can be used on materials that have different substrates and surface textures. Paint gauges show their worth when inspecting automobiles for purchase, able to measure different body panels that could reveal hidden layers of body filler.
Follow the paint thickness meter instructions for calibrating the instrument. Most meters have been set at the factory and require no calibration. You might have to turn a dial to "zero" the meter out. Turn the meter on, if you need to test gypsum or drywall paint thickness. Hold the flexible probe with the probe facing the wall, lightly applying it to the surface. Set the dial for single paint thickness and note the reading. The measurement will be in microns.
Take several measurements across the wall, in high and low locations. You can move to another wall and take probe measurements, just be sure to get a good average reading. Keep in mind that if the meter reads abnormally high over a strip or near a corner, this will indicate drywall tape and joint compound.
Refer to a Coating Thickness Calibration Standards Manual for the standard paint thickness of textured drywall. It should range between 75 and 125 microns for a primer and two-coat application. Any jump in micron thickness will indicate an area where filler putty or "Bondo" has been used.
Use a magnetic pull-off gauge for testing paint thickness surfaces on ferrous metals, such as steel used in the body panels of cars. Set the gauge for the type of metal surface you need to measure. For automotive applications, set the gauge for a automotive body panel application. Refer to your Coating Thickness Calibration Standards Manual.
Set the dial on the gauge and place it against the body panel. Pull it slowly from the surface to obtain a magnetic pull-off measurement. Check each panel of the vehicle, high, low and from each side. A combined uniform thickness will appear for the e-coat, primer layer, base and clear coats. Generally, the accepted limit will be below 125 microns.
Check all fender, hood, door, top and trunk panels. If the digital indicator reads abnormally high in any areas, apply the gauge to the suspect area and try to get an outline of the overly thick location. Such high readings will indicate body filler or fiberglass patching, where the vehicle has been in an accident. Moderately high readings will indicate a panel that has been repainted over a previous coat.
