Chimneys bottom to top

How to ensure that all the components are in good working condition.

By Mary Ellen Polson

One of the joys of owning an old house is touching match to wood on the Þrst chilly day of winter. Before you set the kindling in the grate, ask yourself one question: Is your Þreplace safe? You wonÕt know unless you have it thoroughly inspected and cleaned by someone who knows chimneys.

ÒA chimney sweep is a ÞreplaceÕs best friend,Ó says Dale Pope, a building consultant and home inspector in Gloucester, Massachusetts. ÒA good one will examine your whole chimney system from the basement to the cap. Most of the better sweeps will do repairs.Ó

Chimneys in old houses are rife with potential Þre hazards. YouÕll need to insure that all components of the chimney system are in good working condition. WeÕll start from the ground up.

¥ Foundation. The chimney, Þrebox, and ßue should rest on thick, reinforced masonry in good condition. Give the chimney a once-over for soundness. Look for cracks and settling at the foundation, weathering of the masonry, or any evidence that the chimney is moving away from the house. Clean up any debris around the foundation and inside the ash cleanout, if your chimney has one. Deposits of old mortar and fallen brick are warning signs of deteriorating masonry further up the ßue. If you see dripping water on or around the base of the chimney, you may have a condensation problem or an improperly ßashed chimney. ¥ Hearth. Many picturesque old brick and tile hearths are laid directly over wood subßooring or framingÑdangerously close to an open Þre. (Before this century, it was common practice for builders to support ßoor joists and other framing right on the chimney brickÑplacing combustible materials in close proximity to the Þrebox, and tying the structural support for the house to the overall soundness of the chimney.) Over time, wood exposed to high temperatures oxidizes, lowering its ßashpoint. ÒAt some point, the wood will reach the ßashpoint and youÕll have a Þre in the chaseÑthe space between the chimney and its base,Ó Pope says.

To check for wood framing or old wooden forms, pull out a loose tile or cracked brick from the hearth. You should Þnd a shallow brick arch spanning the hearth space. If the hearth lacks such masonry support, it may be necessary to rebuild it. While this type of project is beyond the scope of this story, a noncombustible, reinforced concrete slab can be poured in place over new framing.

¥ Firebox. All Þreboxes should be lined with Þre (refractory) brick and Þreclay mortar. Your chimney sweep or technician should be able to tell whether your Þreplace meets this standard. Replace any broken or missing bricks, as well as crumbling or missing mortar. Houses built since the 1920s may have steel or cast iron Þreboxes or dampers. If theyÕve been distorted by excessive heat, replace them.

¥ Throat and Damper. The throat is a slot-like opening just above the Þrebox. Narrow and tightly focused to create a good draft for the ßames, smoke, and combustible gases that pass into the ßue, the throat should be Þtted with a damper. If the chimney doesnÕt have one, a damper should be spot-bedded just above the throat, or alternatively, at the top of the chimney.

Check the throat, damper, and smoke shelf (directly under the ßue, in plane with the base of the damper) for fallen debris. If the chimney hasnÕt been used in a long time, you may Þnd electric wires, television cables, or even gas pipes routed through the chimney. Be sure to safely terminate any current before removing these obstructions.

¥ Flue. At least once a year, inspect the ßue for evidence of creosoteÑa black, sooty buildup on the walls of the ßue. Creosote is highly ßammable. An old-time rule of thumb is that the chimney should be cleaned when the creosote buildup reaches the thickness of a dime.

All chimney ßues should be lined if theyÕre used frequently. Because many older Þreplaces have minimally sized ßues, itÕs important that a liner be sized and Þtted by someone experienced in the speciÞc installation method. Otherwise, the ßue may not draw properly. There are three basic retroÞt lining methods for chimneys built without them. Each may require opening access points through walls.

¥ Clay. Clay tile is the traditional material for lining old-house chimneys. These square or circular 2' long tiles drop into place inside the ßue. Clay tile has several disadvantages.

Access holes must be cut through framing at regular intervals the length of the chimney in order to position the tile and seal the joints with mortar. Old tiles can eventually crack and break, opening the way for hot gases and creosote to reach combustible materials.

¥ Concrete. There are several different proprietary methods for this system, which essentially lines the chimney with high-temperature mortar. In one, a rubber bladder is inserted into the chimney, then inßated to the desired ßue size. A lightweight, refractory mortar is poured around the form and allowed to set up. (In another system, a steel bell is used in combination with vibration to position the mortar.) The advantage to this method is that the concrete Þlls in voids and seals them, and also tends to strengthen the chimney.

¥ Stainless steel. Flexible stainless steel liners are lightweight, less expensive, and take less time to install than either clay tile or concrete. Not surprisingly, stainless steel is the most popular liner in both old and new houses, says Harry Richart of CertiÞed Chimney Contractors in Denville, New Jersey. The installer puts a cone on the end of the tube, then winches it into place through the chimney. Once the liner is in place, a lightweight concrete aggregate can be poured around it to insulate the new ßue.

Old, damaged clay and concrete liners can be chipped out with a chipping device hooked onto a drill. If your chimney has an old liner, it can be checked for damage using Chim-Scan, an internal video inspection system manufactured by the Estoban Corp. (515-472-7643). You can do your own visual inspection by looking up the chimney around noon on a sunny day. Use a strong light and a mirror to illuminate the ßue. If the chimney is lined with clay tile, you should see a smooth surface. If you see obvious cracks or patches of brick where the liner has blown out, youÕll probably need a new liner.

¥ Chimney. The chimney walls should be solid masonry, at least 8 thick, with at least 4 between ßues. Check all parts of the exposed chimney for structural integrity. Inside the house, look for thimblesÑmetal sleeves embedded in the chimney to accommodate coal or wood stoves. Often sealed over with lightweight metal plates, thimbles may also be hiding under wallpaper or thin layers of plaster. Wherever you Þnd them, brick them up. Not only do they interfere with the proper draft of your Þreplace, they create weak spots. If thereÕs a Þre in the ßue, those weak spots will be the Þrst to go.

¥ Cricket. Roofs of any considerable pitch should have a cricket, or saddle, to divert water ßow and snow melt. This mini-roof on the uphill side of the chimney can be installed at the same time ßashing is repaired. It should be framed underneath for supportÑnot fashioned solely with sheet metal.

¥ Cap. The simplest cap is a piece of sheet metal formed to the shape of the chimney. It extends down the sides about 6 and is held in place by nails in the mortar joints. It can also be screened to keep birds and animals out of the chimney. A more durable cap extends further down the chimney, encapsulating any projecting masonry. Some chimneys may also have a crownÑa sloping layer of mortar on top of the chimney that sheds water so that it doesnÕt penetrate the structure of the chimney. If the mortar is cracked, missing, or undermining the integrity of the chimney top, it should be replaced.

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