Nothing can mar the look of a beautiful cobblestone fireplace more than the presence of soot or smoke stains. If your attempts to remove these stains with regular dish soap and water have been frustrated, don’t give up; just change your tactics. You may not have a box of trisodium phosphate in your garage, but it’s worth making a special trip to your local home improvement store to buy one. This heavy-duty cleaner is especially effective at removing soot and smoke stains, making it right up your alley.
Dust your fireplace, before vacuuming with a brush attachment. Move the brush gently over every stone to remove cobwebs.
Lay a thick drop cloth or old blanket in front of your fireplace.
Put on the rubber gloves and face mask. Wrap a loose rubber band around the top edge of the gloves if they don’t fit you snugly. This will prevent the solution from running down your arms, coming into contact with your skin and causing irritation.
Dissolve about 3/4 cup of trisodium phosphate into 1 gallon of hot water in a bucket.
Stand on a step stool so that you can work from the top of the fireplace down. Scrub the cobblestone with the nylon-bristle brush, dipping it into the TSP solution when the brush becomes dry. Stones that are especially dirty or covered with soot may require several applications.
Take a step back from your fireplace. If it still looks dirty in spots, mix a new cleansing solution with the TSP, this time adding ½ cup of bleach. This will add boosting power to the cleanser.
Dispose of the TSP by flushing it down the toilet and flushing several times, or pouring it down a laundry tub drain and running the water for a few minutes.
Fill the bucket with cool water. Rinse the cobblestones with a sponge.