Hi, I'm in the process of cleaning my chimney. I brushed the flue and pulled the wood burner out. It's an 11 inch square terracotta flue. No problem getting the flue clean with a brush. My problem is that when I pulled the insert out, used a light to look up into the smoke chamber, the smoke chamber is totally glazed with creosote. Thick creosote. It won't brush off. Can anyone recommend a product that I can spray on to chemically remove the buildup without having to start a fire in it to do so?