Smoke Chamber Repair in Los Angeles

A fireplace opening is wide; the flue above it is narrow. The smoke chamber is the part of the fireplace that joins the two — a space that starts just above the damper and slopes inward to the bottom of the flue. Smoke chamber repair is about keeping that space smooth and sealed.

At its base, behind the damper, is the smoke shelf — a ledge that catches debris falling down the chimney and helps turn back cold air before it reaches the room. Above that, the walls should rise in an even slope so smoke speeds up as the space narrows and enters the flue without tumbling.

Some masonry fireplaces build the slope by corbelling — setting each course of brick a little further in than the one below, so the walls climb in steps rather than a smooth plane. From below it looks like an upside-down staircase.

Each step is a ledge. Smoke hitting the ledges swirls and slows, and slow, cooling smoke deposits creosote — the tar-like residue described in the stages of creosote. The ledges hold it, a brush struggles to reach into the corners, and the deposit becomes fuel sitting right above the fire.

The joints between the steps are the other problem. Where mortar has cracked or fallen out, heat and combustion gases can pass into the masonry behind, and where wood framing sits close to the outside of the chimney, that is heat reaching wood that was never meant to see it. A rough chamber is not automatically dangerous, but an open one should not be left that way.

Parging is a coat of heat-resistant mortar troweled or sprayed over the inside of the chamber. Built up over the steps, it turns a staircase into a slope, closes the joints, and leaves a surface that sheds deposits and sweeps clean.

The chamber is cleaned first. Mortar will not bond to soot, and it certainly will not bond to glazed creosote, which may need creosote removal before anything else happens. Loose material comes out next. Crumbling mortar is raked away, and brick that has come loose is reset or rebuilt, because a smooth coat over a failing wall only hides it.

Then the parging goes on, usually in more than one coat where the steps are deep, using a material made for fireplace heat rather than an ordinary mortar mix. The damper frame and the smoke shelf are part of the same job, since gaps around the frame are a common leak point.

The lower part of the chamber can be seen with a flashlight through an open throat damper. The upper walls, the joints between steps and the connection to the flue are harder, and that is where problems tend to hide.

NFPA 211 recommends annual inspection of chimneys and fireplaces and describes three inspection levels as industry terminology. What each level covers, and when a more thorough look is usually called for, is explained on the chimney inspection page. If you are buying a house, ask what the inspection you are paying for actually reaches.

Parging is the right answer when the chamber is corbelled or rough and the brick behind it is sound, or when joints have opened but nothing has come loose.

Rebuilding part of the chamber is needed when brick is loose or missing. That is masonry work first and parging second. If the firebox below is also failing, firebox repair is often scoped alongside it.

Neither when the problem is higher up. A cracked flue tile is a liner question, and a smooth chamber will not fix it.

Where a masonry fireplace dates from before smooth chambers became standard practice, the chamber may still be the original corbelled brick, never parged. That is worth knowing before a house changes hands or a gas log set or insert goes in.

Burning dry, seasoned wood keeps deposits down in any chamber, rough or smooth; EPA Burn Wise covers wood-burning practice in detail.