Stain is notoriously hard to remove from wood. Some types dye its surface, while others carry pigment deep into the pores. The only real solution is to remove the top layer of wood by sanding, and light-duty sandpaper just won't cut it. The best all-purpose sandpaper for removing stain is 100-grit.
First Things First
It's likely that you're removing stain from finished woodworking. If it's already been coated with a film-forming topcoat such as lacquer or varnish, it will need to be removed first.
Sanding off a topcoat is even more difficult to remove than stain. Save time and effort by removing the topcoat with chemical stripper. Brush it on, and when the topcoat gels in about three to five minutes, scrape off the finish with a flat stick. Follow the instructions printed on the packaging. Unfortunately, chemical strippers won't work on stain.
What to Expect
After your project is sufficiently dry -- about four hours -- and free of topcoat, you're ready to sand off the stain. When you're finished, the wood should look bare and display its natural color. If you can see dark streaks where stain has penetrated deeper into grain lines, you're not finished.
The majority of experienced craftsmen, cabinet shops and production woodworkers rely on 100-grit sandpaper for everything. Some woodworkers argue that finer grit sandpapers -- anything above about 200-grit -- are the only way to go. But high-grit sandpapers work you to death, fill up with gunk, polish wood and cause stain to appear blotchy. Save higher-grit papers for sanding topcoat.
Grits lower than 100 -- 60- to 80-grit, for example -- are too coarse. It might be tempting to use them to remove stain because they remove material fast, but they also cut and scratch wood, and then you'll have to remove the scratches with 100-grit paper.
Attach 100-grit sandpaper to a hand-sanding block; the hard rubber type is best. Begin stroking the wood with the sandpaper. The type of stain will dictate how much effort is involved in removing it. If it's pigmented stain, the sanding block builds up with gunk after only a few minutes. If this happens, change the paper immediately, and keep changing it as often as needed. If the stain is dye-based, you won't have to change it as often.
Go With the Grain
Sand parallel with the grain only. Never sand perpendicular across the grain. This will result in scratches that are extremely difficult to remove. Work with a back-and-forth motion, moving the sanding block about 4 to 6 inches at a time. When the wood becomes bare and free of stain, advance the block forward, and repeat, working in manageable sections, overlapping them slightly each time.
If you're still uneasy about using 100-grit, it's acceptable to use 120-grit, but it's more work, and you'll be changing the paper more often. The additional smoothness of the wood is almost imperceptible. If you're still not convinced, resand it with 120- or even 150-grit