Question: I have two questions regarding creosote buildup in a flue. 1) Is it the loose soot type material which falls when i brush out the flue or is it the shiny build-up on the walls of the flue that cause a chimney fire? 2) If I had a professional clean the flue would he remove the shiny buildup? Answer: 1. It is the sticky stuff that you cannot get off (class 3 creosote) that causes the worse fires. 2. In most cases, they cannot get it all off unless you pay them a couple hundred to use the industrial solvents. Use of certain chimney cleaning compounds sprayed on the wood or into the fire can help remove this over time.