Power Washing and Roof Cleaning Forum

Wow, that's a tough one, no pun intended. Creosote is almost as bad as calcite! It depends on how heavy it is. Without a picture, I'm assuming it has run down the chimney onto the siding. Hot water is a must. If it's heavy some scraping might help first along with hot water. Then apply some good degreaser straight from the container. Allow some dwell time and brush with a stiff brush. Continue without and expectations. Search on chimney sweep suppliers. There might be something there.