Surface
Body filler repairs: what a paint gauge reading can show
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.
Also listed as body filler, plastic filler, filler
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Short answer
Body filler sits between the paint and the metal, so a magnetic or eddy-current gauge counts it in the total. In a DeFelsko case study most of a car read 105-115 µm while one lower front panel read 270 µm and then 930 µm: plastic filler over a rust repair. DeFelsko also says no reading may mean the coating is beyond the gauge's limit, and warns that steel particles in filler can fool some magnetic gauges.
Key facts
- Material
- Filler over a metal repair (plastic filler in DeFelsko's example)[1]
- Gauge method
- Magnetic or eddy current, as for the panel underneath[1]
- Gauge mode
- Fe on steel, NFe on aluminum[2]
- What the reading includes
- Paint plus filler down to the metal, as one number[3]
- Published thickness figures
- DeFelsko case study: 105-115 µm around one car; 270 µm and then 930 µm on a filled lower front panel[1]One vehicle, not a threshold.
- Polishing note
- Not confirmedNo source we checked covers polishing over filler repairs.
- Inspection tip
- No reading may mean the coating is beyond the gauge's range, which DeFelsko says could mean filler[1]
Watch out for
- Steel particles can fool some magnetic gauges. DeFelsko warns that some magnetic instruments can be fooled when steel particles are added to body filler.
- Check extreme numbers against the range. AUTO BILD's 2021 test found three near-identical budget gauges gave some implausible values, including one above 2000 µm on a gauge rated only to 1000 µm. Those were specific models, but compare any extreme reading with your gauge's stated range.
- Tin filler is a different case. On a steel body, AUTO BILD says tin-filled repairs need NFe capability to find. See tin-filled repairs.
What fits
Product details below are the seller's own description unless a source is shown. Pick the variant named for each item.
Fe/NFe combination gauge
UNI-T UT343E Fe/NFe coating thickness gauge (Bluetooth, 0-2000 µm)Choose the UT343E (Bluetooth, 0-2000 µm), the only variant listed.
UNI-T specifies it for ferrous and non-ferrous substrates with automatic or manual substrate identification. The AliExpress store uses UNI-T's name, but UNI-T's own where-to-buy page links no AliExpress store, so treat the seller as unconfirmed. UNI-T's page lists CE and UKCA marks only.
Sold by UNI-T Official Store
View on AliExpress Opens aliexpress.us
Questions
Can a paint gauge detect body filler?
It can show unusually thick readings, as in DeFelsko's case study where a filled panel read 270 µm and then 930 µm against 105-115 µm elsewhere. The gauge shows thickness, not the cause, and steel particles in filler can fool some magnetic gauges.[1]