Whether from a sudden fire or years of cigarette use, smoke damage can besmirch a wall with unsightly black or yellow staining and a lasting acrid stench. Surface damage can be cleaned with dedicated scrubbing, but deeper staining requires a sealant that locks the smoky smell into the wood, freeing you up to paint or paper over and forget about the damage. Two kinds of sealant are used: acrylic and shellac-based. Before applying either, walls must be prepared adequately.
Before applying a sealant, the surface must be thoroughly cleaned of excess smoke and ash. Without preparation, the sealant won't do its job of forcing the smoke under the surface, and you may be left with a blackened, smelling sludge that's worse than what you started with. Lay down a sheet or newspaper, and mix warm water with a trisodium phosphate (TSP)- based cleaning solution. Don dishwashing gloves, and wipe the wall down thoroughly with the TSP mix, vigorously wiping your way up the wall in circular motions, then rinsing off and allowing the wall time to dry before applying the sealant.
If staining is not severe and you are planning to paint your wall anyway, a standard acrylic-based base coat may be all that's required to seal a light smell into the wall and prepare the surface for a fresh coat of acrylic house paint. Apply at least two layers of acrylic base coat to a dry wall, and wait for these to dry thoroughly before proceeding to paint the wall with your final colour. Strong stains that show through visibly after two base coats will probably not be sealed by this method, particularly if the wall's final colour is a light colour.
The more heavy-duty option for sealing persistent, dark or strong-smelling stains is a latex-based shellac sealant. These solvent products will seal even quite severe stains and stenches within the wall but can also be damaging to your skin, so wear gloves and goggles while you apply them. Use a fresh roller to coat the dry, prewashed wall thoroughly with sealant, and ventilate the area well for 24 to 48 hours while drying.
Walls coated with an acrylic base coat should be painted with acrylic paint to secure the sealant and lock the smoke stain into the wall. If the wall has been treated with shellac-based sealant, you have more options: either paint over with a water- or oil-based paint of your choice, or apply wallpaper, which will have the added benefit of covering any remaining visible traces of the stain. Once the final paint or paper has been applied, walls can be cleaned or washed just as any other wall.