How to Check For Bondo Body Filler in a Car Body

Before you buy that used car you may want to check to see if there was ever any body filler repairs done. Is it all metal behind the paint or body filler too?
This process will detect larger filled areas but may not detect very small areas of filler. Anybody can do this!

Difficulty: Easy

Instructions

Things You'll Need:

• Good lighting, natural or artificial
• Scratching awl or pointed metal pick (This is an "optional" tool if you are at liberty to do some poking and probing through the paint)

1. Start out by squatting down along the rear side of the car and view forward keeping your eyes along the profile of the body lines, looking for any waves, dips, lumps or imperfections, which is a clue of present body filler.

2. If you see any waves, dips or lumps go to that area and using the knuckles on your hand begin to knock-knock-knock along the suspicious area and also around the area. The knocking pressure would be similar as if you were knocking on a door to get someone attention!
   You want to hear a metal sound and not a dull thumping sound. Practice a bit ahead of time if you can, metal has a distinctive sound and body filler has a dull sound.
   Ideally you should knock-knock along all sections of the car, particularly on the lower sides.

3. You also want to look very closely into the paint in suspicious areas to see if you can spot any cracking or splitting in the paint which could represent body filler that has shrunk and left open splits.

4. 

   If you are liberty to poke a little and you have your awl or pick with you, you could actually poke into an area and scratch out body filler if it is there.
   If there is only metal behind the paint you will only scratch out the paint and layers of primer and hit metal. Big difference in scratching out body filler. It will be chunky and much thicker than just paint and primer.
   A hot spot for bondo filler, especially on older cars, would be just below the rear quarter panel, behind the rear wheel. This area tends to rust out quicker, especially if the car came from the Midwest where a lot of road salt is used.

Tips & Warnings

• Best to do this type of checking in good natural lighting where you can get a good view of the profile of the car and to be able to look "into" the paint.
• Keep in mind that on many repairs, such as a rust hole maybe 6 inches in diameter, that it would be typical for some filler to be used "over new metal" welded in place. The knocking test will detect the metal only if the layer of filler is thin and just meant to cover the metal and then smoothed out. The real concern is when there is only filler with no metal close behind it!
• Always get permission from the seller before you do any probing or scratching with your pointed awl or pick!

[kredding]

on 11/14/2007 Great Article!