Detecting galvanising: how to find a replaced panel

Factory galvanising is a layer of zinc applied to the steel sheet before that sheet became a body panel. Painting does not restore it and no brush applies it: it is either there or it is not. That is why missing zinc says more about a replaced panel than any thickness figure can.

The paint thickness of a neatly painted replacement may be no different from its neighbours — and usually is not. The galvanising is always different.

The gauge distinguishes not only the coating but the substrate beneath it: zinc behaves differently in a magnetic field from bare steel. The detector flags it as a separate sign rather than adding to the thickness — on the screen it is not a second number but an answer: there is zinc under the paint, or there is none.

The conclusion, though, comes from the whole car rather than one panel. If every panel has zinc and one does not, that panel was almost certainly replaced. If there is no zinc anywhere, the body simply is not galvanised: not every manufacturer does it, and not in every generation.

The typical case is a car repaired carefully by a good shop. The door was replaced with a new one, painted in a booth, and the layer went on evenly: 138 µm against 129 on the panel beside it. There is a difference, but it fits inside the factory spread, and no conclusion can be drawn from it.

That is the line between two questions. A resprayed panel may be the result of a car-park scratch; a replaced one points to something far more serious. A gauge that only measures thickness never asks the second question.

Compare in two directions. Symmetrically: left wing against right, left door against right. And along the side: if zinc is present the whole way and one panel has none, that is your find.

Start with the roof, as you do with thickness: it is replaced least often and serves as the anchor for comparison on this particular car.

Bolt-on panels — bonnet, doors, boot lid — are replaced more often than wings and pillars, and it is on them that a galvanising check yields the most findings.

The threshold is the point from which the gauge treats a signal as galvanising. On the AVTOPODBOR line it can be moved to suit a particular body: lowered to catch a thin layer of zinc, or coarsened to show only clear findings. On the DPM-816 line the threshold is fixed — set with a margin against false positives.

Galvanising and magnetic filler detectors are fitted to every CARSYS gauge intended for car bodies: the AVTOPODBOR line and the DPM-816 PRO, LITE and COMBO. What differs between the lines is not whether the detector is there but whether its threshold can be adjusted.

The industrial version of the DPM-816 has no detectors, and that is not a cut-down build: it is made for coating control in production, where thickness is measured to a procedure rather than searched for traces of repair on a body.

On plastic bumpers and trim there is nowhere to look for galvanising: there is no metal underneath, and the gauge gives no reading at all.

And a second caveat, without which the argument turns into a promise. Missing zinc on a panel is a strong point but not a verdict: there are models and generations with no galvanising at all, and panels galvanised only in part. So the comparison is always made within one car, not against a reference table.

You need a gauge that separates zinc from steel rather than producing a single combined figure. Every CARSYS body model does this — there is no separate “gauge with galvanising detection” to hunt for.

The AVTOPODBOR line adds an adjustable threshold for both detectors and a colour helper: green for factory coating, amber for thickening, red for a likely repair. The DPM-816 PRO offers five measurement modes and a comparison mode. Choosing between them is a question of how often and in what conditions you inspect cars.