Daily Answer is excerpted from the JustAnswer archives and features information provided from a Expert on JustAnswer.
Q: How do I remove soot from my stone chimney and fireplace? I tried soap and water without much success.
A: Using water is not recommended. Once mixed with water soot becomes harder to remove, as it turns into a tar-like material. The proper way to do it is to use dry methods.
You first brush it lightly with a vacuum machine to pick it up (if possible with the exhaust outdoor to make sure smaller particles don't become airborne in the house). You then use a soot sponge (usually available in hardware stores) to remove what remains.
You can still probably remove a lot that way even after using water. But water probably caused a stain, and you may have to use abrasive to clean it now. This is not a problem if the stone was rough, but it may damage polished stone and require a new varnish sealing if one was present. A good soft and cheap abrasive is sugar, bit it may not be enough if the water glued too much on the stone. A sand blast machine may work well.
To have less abrasive option it's possible to use walnut shell powder as an alternative -- it does a good job. Any cleaning may change the color compared to the untreated area, so you may have to consider treating the whole area.
-- Answer from Martin Caron, a home and garden Expert on JustAnswer.