Prevent Corning When Sanding Shellac

One of our members recently wrote in, with a question, and the question was, works with dewax shellac all the time, and finds that when he goes to sand the shellac, he ends up getting a lot of corns on his sandpaper. So, first thing I think that we need to do, and the question is, "What's the deal with that, where's this coming from, what's causing it?" First thing I think we need to do, is help you with, what corn on his sandpaper, where's the corn coming from? I don't think you use corn to make shellac, you use bug poop, right? Well, it's not corn, it's corns. I happen to have a piece of sandpaper here, that's pretty corny, What happens, is that, sometimes when you sand a finish, for a variety of reasons that we're going to talk about, you get these corns or balls or chunks of finish on your abrasive.

One thing that happens then, is that is clogs up your abrasive really quickly, it's not going to sand anymore. Another is that, you can actually start to ruin your finish, because these are actually like little balls of finish that are sticking up, and if we keep running this over the top of our finished surface, they can start to leave marks on there. This shouldn't happen, you should be able to sand any topcoat and clean it up, sand it smooth, put on another layer without this happening. So, what can make that happen with shellac? A couple of things.

One, is that, it's possible you simply sanding the shellac, before it has the opportunity to dry completely. So, you've got to be patient, give it a chance to dry, then do your sanding. Another, for this, could be, you putting the shellac on too heavy. So, in that case, even though you think you're giving it ample drying time, the layers of shellac aren't dry all the way through, and probably never will be, and as a result, when you start sanding, you're exposing those wet layers below. That's what's causing your paper to corn.

Third problem here, could be, shellac has a shelf life. So, the reason I've got this piece of plexiglass sitting here, is, there's an experiment you can do. Brush some shellac onto plexiglass, the reason that we're putting it on here, is, we don't want it to soak in. It should be able to lay a thin layer, should be able to lay on the surface, and dry to a point where, when we scratch it, it scratches. When I do this with my thumb nail, I'm not peeling a layer off, like a layer of rubber cement.

It's scratching the surface, that tells me that this can of shellac is still okay to use, because even on this non-porous surface, it created this nice hard layer that my thumb nail is abrading, and that tells me I can still go ahead and move forward using this shellac. If, when you do this, it's kind of rubbery, It's not hardened, it's coming up like contact adhesive, that tells you, that, that shellac has probably gone bad, and you shouldn't be putting it on your projects. Key to this, is, just like on your projects, this has to be a thin layer of shellac. The other thing that can happen, is, if your power sanding your shellac, it could be, that the heat of the sanding operation, is melting the shellac, that's causing it to corn into your abrasive. So it's possibly you'll want to slow the rpm down, on a power sander or simply stick with hand sanding in between coats.

This sandpaper is all corned up. I've got a board here, that's got a layer of this shellac on it, it's nice and dry, we should be able to treat that dewax shellac, just like a sanding sealer. So, once that's dry, we should be able to scuff it down, without getting any corning in that paper. Once we've knocked the high points off of it, that's nice and smooth right now, it's ready for another coat of shellac, coat of lacquer, coat of polyurethane, whatever your topcoat is of choice. So shellac is fully capable of acting as a base coat, being sanded out, without corning, provided you treat it the right way.