Tackling soot in your fireplace is a really messy, hands-on job. Though it might be tempting to use a powerful commercial cleanser to get the job done quickly, think about trying one of these all-natural options first; they are safe and just as effective as most commercial cleansers.
Before you do any scrubbing, remove all ashes with a shovel or dustpan and place them in a sturdy bag. Sweep out any remaining debris and follow up with the brush attachment on your vacuum (and don't forget to clean the brush attachment afterwards —you don't want to spread soot around the rest of your home!).
A kneeling board or folded up towel will come in very handy while working on this project. And it's a good idea to put on gloves, a face mask, and protective eyewear to keep the soot from irritating your lungs and skin.
I tested three different natural cleansers on my very old fireplace and have to say that I was most impressed with a simple paste made with water and cream of tartar. The vinegar and water spray did the job, but didn't yield as great a result as I would have liked, and took the most scrubbing on my part. The baking soda and dish detergent paste worked just about as well, but again took a lot of scrubbing on my part.
Cream of Tartar + Water In a bowl, combine about 2 tablespoons of cream of tarter and a bit of water to make a thin paste.
This method works best when used on smaller, concentrated areas like the surround or on the hearth. It yielded the best results when compared to the other two methods, but unless you have access to large, bulk quantities of cream of tartar, you might stick with baking soda or vinegar for the interior of your fireplace.
Apply a layer of the paste to the sooty area and let sit for 5-10 minutes.
Rinse with warm water, repeat steps if necessary.
Vinegar + Water Mix equal parts vinegar and water and combine in a spray bottle.
After using a dry brush or sponge to remove as much loose soot as possible, spray the bricks with the solution. Let it sit for a few minutes and spray once more. While the bricks are still wet from the second application, take a scrub brush and work from the bottom up (to avoid streaking) in small circular motions. It is a good idea to follow up with a baking soda + water wash to neutralize the acidity of the vinegar on the bricks. If your fireplace is older than 20 years, you may want to opt for a less abrasive cleaner and steer clear of the vinegar solution.
Baking soda + dish detergent Add about 2-3 tablespoons of dish soap to about a half cup baking soda to make a paste.
You're not really looking for a thick consistency, you want it to be able to spread it on the wall with ease, so you might end up adding more than 2 tablespoons of soap.
Dip your scrub brush into the paste and scrub in small circular motions from the bottom of the brick up, to avoid streaks. Let the mixture set on the wall for a few minutes before rinsing with warm water. Repeat the steps if necessary.
After the side walls of the fireplace have been cleaned, finish up by washing the bottom of the fireplace and the hearth. Keep old rags on hand to soak up any dirty water that has run off from scrubbing the walls, then apply your cleanser, scrub, rinse, and repeat until clean.