Reference
Car paint and body surfaces: what to measure and how to polish
Pick a surface to see which gauge type can read it, what its paint layers look like, and what to check before polishing it.
Choose your surface to see the key facts. Each one links to its source on the full page.
Metal body panels (steel and aluminum)
Steel panels need a magnetic (Fe) gauge, aluminum panels an eddy-current (NFe) gauge. Both read the whole paint stack down to the metal.
- Steel body panels steel panels, ferrous panels, Fe panels
- Aluminum body panels aluminum panels, non-ferrous panels, NFe panels
Non-metal panels (plastic and fiberglass)
Magnetic and eddy-current gauges need metal under the paint. Paint on plastic bumpers and fiberglass is measured with an ultrasonic gauge.
- Plastic bumpers and mirrors plastic bumpers, bumper covers, plastic parts
- Fiberglass panels fiberglass, GRP panels
Other paint and surfaces
- Clear coat Fe/NFe gauges cannot isolate clear coat. DeFelsko's 35-50 µm typical figure and 8 µm removal statement, and why they are not OEM specs.
- Factory (OEM) paint DeFelsko, PPG Refinish (Australia/New Zealand) and AUTO BILD publish different typical factory paint ranges. Why none is a pass/fail number.
- Refinished (repainted) panels Compare adjacent panels and mirrored spots. Published repaint figures from AUTO BILD and PPG, and why a reading is not proof of an accident.
- Body filler repairs Filler adds to the reading, and very thick filler can push a gauge past its range. DeFelsko's case study and why some magnetic gauges are fooled.
- Tin-filled repairs AUTO BILD notes that tin-filled repairs on a steel body show up only on a gauge with NFe (eddy-current) capability. What that means for buying a gauge.