Official Luthiers Forum!

Wet sanding keeps the paper cool so that you don't get the hard little "corns" on the paper. The corns are melted together finish (shellac or nitro) welded to the paper. It is bad enough when paper loads up with well behaved dust, but even the smallest corns cause the paper to start making scratches as if the paper was a lower grit number. Wet sanding makes sure that you can quickly work your way through finer and finer papers.

You can still get corns when wet sanding. Sometimes they can be brushed off the sandpaper by dragging it over a terry-cloth towel.