Body filler is a compound used for patching or filling holes or dents in vehicles. After spreading the body filler into the hole or dent, sand the compound properly to create a smooth finish for painting. Sanding body filler is a time-consuming, tedious job that requires attention to detail and multiple layers to complete with perfect results.
Remove edges of the body filler with a 10-inch, half-round body file. Hold the file flat against the body filler and scrape off the high spots. Work in more than one direction if possible to reduce scrape marks in the body filler.
Spray the body filler with a light coat of primer. Use only enough to lightly coat the surface.
Attach 60-grit sandpaper to a 10-inch sanding block. If the area is very small, use a smaller sanding block. The sanding block should be slightly larger than one half the size of the patch area.
Sand the area with the sandpaper on the sanding block in long strokes to prevent making shallow, wavy areas in the body filler. Move the sandpaper in multiple directions to avoid creating scratches in the body filler. Sand up and down, side-to-side and in circles, changing directions frequently.
Remove all of the primer. If there are low spots, clean the area and fill the low spots with additional body filler. Repeat Steps 1 to 3 until the area is level when the primer has been sanded out with the sanding block.
Replace the 60-grit sandpaper on the sanding block with 80-grit sandpaper. Sand the entire area and a margin around the area. Sand the patched area with the 80-grit sandpaper until there is a ½-inch margin around the body filler that is bare metal. Continue sanding to expose an additional margin of ½-inch original primer (usually white) and blend the area so the edges of all layers are visible and blended into each other.
Change the sandpaper on the sanding block from 80-grit to 120-grit. Sand the entire area, including the margins, until smooth. Repeat with 220 sandpaper.
Spray the area with a thin coat of primer. Sand the patched area with 220-grit sandpaper on the sanding block and check for pinholes, depressions and other imperfections. Fill with additional body filler if needed and start with 120-grit sandpaper on the sanding block to remove the skim coat of body filler. Repeat sanding with 220-grit sandpaper.
Finish sanding with 600-grit wet sandpaper over the entire area. Keep the area saturated and sand up and down, left to right and in swirls to smooth out all sanding lines and create a smooth surface that will not have imperfections.
Take your time with each sanding step for the best results. You cannot over-sand, but not sanding well enough will leave marks that will show up in the finished paint.
Wear a dust mask while sanding to prevent inhaling the body-filler compound. Work in a well-ventilated area.