Soot out of a fireplace, burning a fire could depart black smoke stains in your plaster walls. Since soot is fatty, it adheres to surfaces and may smear or spread when it is cleaned with water or other cleaning products. For easier removal, dry-cleaning methods should be used first, followed by washing with warm water and white vinegar. The vinegar may get rid of any remaining soot in the plaster walls and neutralize the odor.
Open any windows to ventilate the region while cleansing smoke and soot stains.
Vacuum as much soot as you can from the plaster walls, using the nozzle attachment. Hold the nozzle about 1 inch from the wall to prevent smearing the soot when vacuuming.
Wipe the plaster wall using a dry-chemical sponge to remove the soot.
Fill a bucket with equal parts of white vinegar and warm water. Dip a sponge into the solution and scrub any remaining soot in the walls. Rinse the sponge in the bucket, as needed. Allow the walls to air-dry.