I watched a youtube video from a guy called "The GunMan" about removing runs in paint. He spoke with a pretty thick down under accent. His trick was to apply "fine filler" over the runs to create something to protect the finish on either side of the run from being sanded down to metal. Also, it acted like a gauge- sand through the filler to the finish, and the run has been sanded off as well. Pretty slick. So, my question is- what is "fine filler"? I've not heard that term before. Thanks.