Hmmm didn't have to do this with mine, since I added the water before cutting with the plasma cutter. But I would suggest getting the wire brush attachment a drill, or grinder and try that first. If that doesn't work you may have to take a grinding wheel to it. Although I'm sure this has happened before. I faintly remember seeing it somewhere on these forums I believe, but I'm not sure where. So do a search, and you may find the answer if what told you isn't the right thing to do.