Creosote is an oily residue that is produced by burning wood. Essentially, it starts as a vapour and sticks to the bricks inside your chimney. As it dries out it becomes flaky and smelly. There are plenty of commercial products that will help to reduce the creosote that your fireplace produces, but it will not totally be eliminated. Cleaning the creosote from the brick can be a time-consuming and messy job, so be prepared to get your hands dirty.
Fill a spray bottle with hot water. Saturate the area that needs to be cleaned. This helps to keep small particles from falling on you during the cleaning process.
Cover the area with WD-40 or eucalyptus oil. The oils will break down the creosote and make it easier to clean. Let the oil sit on the stain for 30 minutes.
Scrape the area with a hard wire brush. You may have to scrape for quite a while if a lot of creosote has built up over time.
Mix dish detergent into a bucket of hot water. Pour enough dish detergent into the water to get a nice sudsy mixture.
Dip the wire brush into the detergent mix and scrub the stained area.
Rinse the area off with a spray bottle full of hot water.
Work smarter, not harder. Apply the oil to the stain, wait and then clean the area enough to remove the surface creosote. Continue this process. This method takes less elbow grease, but will take longer to finish the project.