Filler Finder

It's been said that rust never sleeps—unless it's completely removed—rust will continue to eat up good sheetmetal until it's no longer salvageable. Not surprisingly, some repair facilities fix rusted-out areas by simply patching the spot with body filler and paint. The same holds true for damage resulting from a collision. It's a lot quicker to use filler than to take the time to pull the panel and handwork the metal.


Yet body filler is not a desirable addition to any collector car. Unfortunately, many buyers are not experienced enough to spot a filler repair, do not do a thoroughly inspection and consequently pay too much for the vehicle. A handy way to find hidden body filler is with a magnet. Wherever there is filler, the magnet loses power and will not stick to the material beneath. The thicker the filler, the weaker the magnet, to the point it actually falls from the panel that's being inspected.


Wise car enthusiasts always take along a magnet when looking at a prospective purchase. It's really the only way to find out if the vehicle has had collision damaged and been improperly repaired. This handy little item is available at automotive specialty shops and paint & body-supply outlets. It not only finds areas with filler, it also approximates how thick the filler is. Check it out.

Solid Metal
This magnet has a sliding case that is held to the metal surface by the tip of the magnet. As you pull the magnet back, the top of the clear case slides along a 1/8-inch scale. The farther you can pull the magnet back, the more real sheetmetal is in that spot. The tip of the magnet doesn't contact the paint so you don't have to worry about scratches—and you can go around the entire vehicle, taking several samples from each panel. This demonstration shows the magnet pulled out past the #10 mark, which indicates solid metal at that spot.

Filler Found
We moved to the rear quarter panel, which has a poorly repaired area above the rear wheelwell. We put the magnet on the paint above the area that had been repaired, and it clearly indicates that this panel contains filler above the primer. It's relatively thick in this area under the paint since the magnet holds to the #8 mark. This indicates approximately 1/4-inch of filler. That's a lot—and it doesn't look like it's going to get any better in the damaged area below. Filler this thick will break apart over time, leaving spider-web cracks in the surface paint.