Q. In a recently purchased house, one of the bedrooms was used as a smoking room by a previous owner and still smells of cigarette smoke. To get rid of the odor, my clients washed the floors, walls, ceiling, and all the windows and woodwork, then used water-based Kilz on the ceiling, walls, and woodwork, followed by two coats of latex paint — yet the odor persists. What is their best plan of action at this point?

A.Fernando Pagés Ruiz, a contractor specializing in fire restoration in Lincoln, Neb., responds: Smoke smells of any kind can be frustrating to remove, because smoke permeates walls and other porous surfaces and can get trapped in household ducts. If not properly removed or encapsulated, smoke odor reoccurs, especially during warm or damp weather. Although your clients had the right idea to encapsulate the odor with a sealer after a thorough surface cleaning, they used the wrong products. Smoke smells require odor-neutralizing cleaners, and while water-based Kilz has excellent stain sealing power, it doesn't really block odors.

Here's a four-step approach I've found to be effective in getting rid of smoke smells: First, remove and replace any existing porous materials in the room, such as carpeting, pads, and drapes. Second, clean the walls, ceiling, and floor with a chemical designed to mitigate smoke odors, such as Bridgepoint's Smoke Odor Counteractant (Bridgepoint Systems, 800/794-7425, www.bridgepoint.com) or Chemspec's Air Neutralizer (Chemical Specialties Manufacturing Corp., 800/638-7370, www.chemspecworld.com), along with a heavy-duty wall cleaner like TSP. Don't forget to remove heat registers and clean inside the register boot.

Third, if you have access to a hot fogger (available at many equipment-rental shops and professional carpet-cleaning outlets), thermal fog the room. While there are several "flavors" of odor-eliminating thermal fog, the candy-scented ones tend to mask smoke odors best; I've found Bridgepoint's cherry-scented Thermal Fog to be especially effective. If you can stay out of the house for a few hours, you could also place an ozone generator in the room, and then air out the room after about four hours of treatment. Both hot-fog and ozone treatments will chase away smoke smells in areas that are inaccessible to surface cleaners and sealers.

Finally, apply a smoke and soot sealer to the walls, ceilings, and (if possible) subfloor with a paint sprayer, wet fogger, or garden sprayer. Unlike Kilz, chemically engineered smoke sealers deodorize and encapsulate smoke odors so they don't become airborne. You can also spray these deodorizing sealers into ductwork.

If these steps seem too complicated, consult a professional restorer. You can find one in the phone book under "Fire & Water Damage Restoration."