There are three ways to remove body filler from a vehicle and each has it's advantages and disadvantages. The most common way is to mechanically sand the old filler. This is time-consuming, messy and expensive because of the cost of sandpaper and man-hours. Chemically stripping is also time-consuming and messy. Heat stripping is fast and not as messy.
Heat the old body filler with a propane torch. Wear a full-face respirator and be sure the car is parked in a well-ventilated area. Work the flame back and forth over the area. Do not work a large area; concentrate on removing a small section at a time. The filler will begin to flame and die down.
Scrape off the filler. The scraper will easily penetrate the heated filler and layers of filler will lift off. Wear leather gloves, since leather is flame-resistant. Work the area with the flame and scrape until all filler is removed. Keep a spray bottle filled with water on hand in case it is needed, and keep a fire extinguisher handy.
Wire-brush the area until all the loose filler is removed. The heat will have deteriorated the bonding ability of the filler and any leftover material in the creases of the old bodywork will brush off.