+50. Removing Dark Stains With Sandpaper Remove the finish over the stain gently with sandpaper, moving with the grain of the wood. Use #100-grit sandpaper, and then feather the edges with #150-grit sandpaper. Sand the stain with #150-grit sandpaper, now that you have removed the finish.ax the wood with a quality polish. Removing Dark Stains With Sandpaper. 1  Remove the finish over the stain gently with sandpaper, moving with the grain of the wood. 2  Use #100-grit sandpaper, and then feather the edges with #150-grit sandpaper.