Use trisodium phosphate, a very powerful cleaning chemical, to clean mild to moderate smoke damage. Dissolve one tablespoon of trisodium phosphate in one gallon of water, and scrub any soot covered walls with the solution. Trisodium phosphate is a very harsh chemical, and using it safely requires gloves, goggles and long clothing. Very sooty surfaces require several applications of trisodium phosphate solution, and some surfaces may retain soot even after repeated washings.
Even if a trisodium phosphate solution completely removes all visible evidence of smoke damage, a strong smoky odor often remains in homes affected by fire. For minor smoke damage, opening all doors and windows may be sufficient to get rid of the unpleasant smell. If the smell persists after a thorough airing out, applying a mild vinegar and water solution to all affected surfaces helps to reduce the smell. A baking soda solution is also effective at countering mild smoke odors, and several dishes of baking soda placed around the room actually remove the smoky smell from the air.
For some walls with extremely thick smoke deposits, even trisodium phosphate is sometimes inadequate to completely restore the original finish. For these walls, either strip the old paint off before applying a new coat, or use a special primer formulated for sealing in soot and smoke odors.