Wet sanding doesn't melt the bondo, the water simply holds the raspings (dust) from sanding in suspension. This allows a natural change in the grit of your sandpaper, creating a gradual smoothing of the part. With wetsanding, you can handle the part as you sand, just like regular sanding. It will create a film as you go along, which you will want to wash off as you go along. Just keep the paper a little wet, keep cleaning as you go. In general, I sand my parts down with 60 grit, then 80, then 100, then 120 with regular sandpaper, no water. Then I switch to 150 and wetsand. IF need be I will then go to 220 and wetsand some more. This will have your parts very very very smooth. If you want, you can go to 400, but you shouldn't need to. If you are going to use filler primer, sand with the 60, 80, and maybe 100. Use your filler primer, then start with the 120 and give it a regular sanding, then switch to the wetsanding. Once you have painted, you can wetsand the paint as well, but start around 2000 grit, then move down. Another quick point, don't use regular sandpaper (the tan colored stuff) to wetsand. There is special paper for wetsanding, it is generally a black color, and will be labeled wet/dry sand. Hope that helps!!
