Sawdust is a form of dust formed from cutting wood.
While detained by the Tandarans, Travis Mayweather told his captor Klev that he didn't think he could hold down another bowl of what he was being fed because it tasted "like sawdust." (ENT: "Detained")
While showing Captain Kathryn Janeway around the newly constructed USS Voyager, Admiral Patterson told her that there was "still some work to be done, but once the saw dust clears I think you'll be impressed." (VOY: "Relativity")