When should I throw away sandpaper?

Article - March 24, 2008

This week’s question comes from Jonathan. He writes:
“So I’ve been doing this woodworking thing for a long time (even though I’m just 40) :-) So there I am in the shop listening to my ipod, hand scraping some stuff, sanding some other pieces (long story) and after a while, the brain starts to drift a little… “I wonder when the hell I should be throwing out these sanding disks…” What is -your- rule for deciding when the 5″ sanding disks on your little Festool have generated enough dust and are ready for the fireplace? (I mean, the disk isn’t frayed or torn. I use klingspor and Norton disks so the things are pretty good quality, and i know after a while a 80 disk probably ends up more like a 120 as the abrasive wears down).”

And here was my reply: “Excellent question Jonathan. Sometimes its really is hard to tell. One common misconception is that as the abrasive wears down, its like sanding at a higher grit. In reality, you aren’t sanding at a higher grit. You are just sanding at the same grit with much less efficiently. :) I usually just look for a few specific signs that tell me the sandpaper is ready for the trash. First is visible wear. That’s an obvious one. For paper that has no visual indicator, I actually just feel the surface. Eventually, the paper will feel a lot smoother when compared to a fresh piece. So how do you know when to switch? Well that’s a personal decision. If you want to save paper, you can wait a long time. But you are doing it at the expense of time and sanding efficiency. In a professional shop where time is more expensive than sandpaper, you switch out more often to get the job done sooner. Its hard to describe just how much smoothness I look for, so you kind of have to decide for yourself. But you should be able to tell when your sanding efficiency is going down. And keep in mind that even dull paper will continue to sand…..but very slowly. Hope that makes sense and gives you at least some guidance. Good luck!”

For some more information on surface preparation and sandpaper, check out this article from FineWoodworking.com

All About Surface Preparation