Working with Filler, technique #1: After letting the filler reach this firm state, it's time to start sanding (it's perfectly fine, it's easier to start before it fully hardens). Have a sanding block ready with your desired grit paper (36-40 for prep and excess filler, 80 for shaping, 120 for scuffing/smoothing, 220 for smoothing, and 400-2500 for wet sanding).
DO NOT sand without a sanding block, this will unevenly distribute pressure, causing "waves" in your bodywork. When sanding a smooth surface (no bodylines, etc.), always sand the whole area, 1-2" past the filler. Never sand one area for any length of time, as this will cause a low spot. In any sanding, sand in an "X" motion 5 times one way, 5 times the next. This crisscross motion will lessen fatigue and work the filler faster. Work filler until you're satisfied. Applying filler may have to be repeated, it's normal. When you become satisfied, you should have been using a smaller grit paper to smooth the area (working from 36-40 to 120). See Prepping for Paint.
Working with Filler, technique #2: Now it's time to start sanding after the filler has reached this tacky state. Use a sanding block with your desired grit paper (36-40 for prep and excess filler, 80 for shaping, 120 for scuffing/smoothing, 220 for smoothing, and 400-2500 for wet sanding).
36-40 grit is very course grit used for excess filler or quickly cuting through old paint to the bare metal for filler work/smoothing work. Also used on grinding discs at high speed to cut down welds prepping for smoothing.
80 grit, most widely used for most everything from stripping old paint to shaping filler.
100-120 used for scuffing and smoothing
180 mostly smoothing filler or scuffing for primer/sealer.
220, used for the last smoothing of filler.
400-1000 wetsanding paper, used for wet sanding prime coats, base coats and clear coats for smoothness and to correct flaws in the finish.
1500-2500 is used for smoothing the final coat(s) of clear just before buffing to acheive that mirror quality. (without distortion depends on your prep work)
Never use anything by bondo brand. All fillers are made by Evercoat are very good fillers. Plastic fillers are used mostly for smoothing (light coat) Most widely used filler for filling dents and dings are fiberglass fillers topcoated with a plastic filler for last smoothing. Metal-2-metal is a good filler, just a bit harder to work with. Harder to mix correctly without exsperience/practice and also harder to shape, but a good filler, it has a high aluminum content.
[ February 28, 2003: Message edited by: Halloweenking ]</p>