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Masonry chimneys
Ash dump area - If your fireplace has an ash dump, it should be free of any combustible framing within the ash dump area. The next time you empty the ash dump check it out with a strong flashlight. If any part of the house framing is visible, DO NOT use the fireplace until this is corrected. The ash dump should have a tight fitting door installed where you scoop the ashes out and a tight fitting cover installed in the firebox floor where you push the ashes down into the ash dump. Both the ash dump door and ash dump cover should be made of noncombustible materials. If either of these are damaged or missing, they should be replaced or repaired before using the fireplace again.
Chimney cleanout - A chimney cleanout is different from an ash dump, but the two are often confused. A chimney cleanout is an area where debris can fall from the chimney flue and accumulate. Chimney cleanouts are usually only found in straight flues serving either a freestanding woodstove, furnace or boiler. This cleanout should extend eight to twelve inches below the thimble, and it too should be sealed with a tight fitting noncombustible door. Replace or repair this door if it is damaged or missing.
Firebox area - The firebox is the area of the fireplace where you build the fire. The firebox should be lined with refractory firebrick. The firebrick may be cracked or the mortar around the bricks weakened by hot fires or years of use. Rainwater coming down the chimney will also weaken the mortar holding the firebrick together. The firebox area takes the greatest abuse during fireplace use, and you should watch this area closely. If the firebrick are loose or if any of them have cracks more than a 1/4 of an inch wide, the firebox should be repaired before using again. Mortar joints between the brick which have eroded back more than 1/2 inch also indicate the need for repairs. Firebox repairs are the most common type of repair required of fireplaces. Depending on frequency of use, expect to repair the firebox every five to ten years. Firebox repairs are an ordinary maintenance item for fireplace owners, just as painting and reroofing are common repairs for homeowners.
Dampers - Every fireplace should have a damper. If yours does not, you should consider installing one. The damper keeps heated air from escaping up the chimney when it is not in use. An open fireplace without a damper will allow more heated air to escape than would be lost by leaving a window open all winter. The damper also helps keep some of the heat generated by the fire from escaping up the chimney, while still allowing the smoke to escape. For repairs, replacement parts are generally available for dampers less than twenty-five years old. Your local chimney sweep or masonry supply company should be able to help you locate these parts. If parts are no longer available or if you do not have a damper, the best replacement is usually a top sealing damper. Your local chimney sweep is the best person to contact for installation of a top sealing damper.
Smoke chamber - The most common repair to a smoke chamber would be parging of the smoke chamber walls. Parging is a coating of mortar applied to the bricks to smooth the interior walls. During a chimney fire the parging is often cracked and damaged. An experienced chimney sweep or brick layer should be able to reparge your smoke chamber.
Flue - The most common type of flue repair is relining. There are many reasons to consider relining your chimney. Several of the more common reasons are:
Repairing damage - Chimney flues are often damaged by chimney fires or lightning strikes but can also be damaged by settling or deterioration of the chimney.
Proper sizing - Chimneys often need to be resized to perform properly if the intended use of the chimney is changed after construction. An example of this would be using a fireplace flue to vent a woodstove. If the oversized fireplace flue is used to vent the woodstove, excessive creosote and tar glaze may result. The woodstove will not perform as well as it could unless it is connected to a properly sized flue. If you have, or plan to have, a woodstove installed in a fireplace, you should consult with a professional chimney sweep to determine if your flue needs relining.
Upgrading old chimneys - Chimneys that were built without flue liners should be lined for safety’s sake. Regardless of their condition, unlined chimneys are always improved with the addition of a liner.
Converting fuels - When furnace or boiler installations are converted from one fuel to another, relining becomes an important consideration. If you have converted your heating system from oil to gas heat, your chimney could present unknown hazards unless you have had the chimney properly inspected and maintained. After oil to gas conversions the sulfur deposits left from years of oil burning mix with water vapor produced by the new gas appliance. This forms an acid which attacks the bricks and mortar in the chimney. The brick and mortar deterioration can lead to blockages in the venting system which can lead to accumulations of carbon monoxide in the home. This deterioration occurs rapidly and should not be ignored.
The common relining materials are:
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Clay flue liners |
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Stainless steel |
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Aluminum |
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Cast-In-Place |
Lets take a look at each one of these.
Clay flue liners - Clay flue liners are the primary choice for new construction but can also be used for relining. Relining with clay flue liners may require cutting open one wall of the chimney to remove the old liners and install the new ones. Since clay flue liners come in two foot lengths they must be properly seated and mortared at each joint. Lowering the clay liners down from the top may not produce satisfactory results.
Stainless steel - Stainless steel is probably the most common relining material. Stainless steel liners are available in round, rectangle or oval shapes and can be made of either flexible or rigid construction. Flexible liners are useful when the chimney contains bends or offsets. Stainless steel liners are made of several alloys, the most common are 304, 316, 321 and AL 294-C. If you are considering having a stainless steel liner installed, the installer should be able to recommend the most appropriate material to use based on the intended use of the liner. Stainless steel liners are insulated to help maintain flue gas temperature within the liner and prevent heat transfer to nearby combustibles. Stainless steel liners can be insulated with either a ceramic fiber blanket or a mixture of Portland cement and vermiculite. The latter is mixed like mortar and either pumped into the chimney or carried to the roof in buckets and poured in. This type of insulation hardens and helps secure the liner in place while sealing cracks in the chimney structure.
Cast-In-Place - This type of liner involves pouring a special mixture of cement and insulation material around a form to create a new flue liner. There are two common methods of cast-in-place liners. The first uses a long inflatable bladder to form the flue. The bladder is installed in the chimney and sealed at the bottom. The mix is then pumped around the former and allowed to cure. After curing, the former is deflated and removed, leaving a new flue within the chimney. Another method involves pouring the mix around a vibrating form and drawing the form up through the chimney as the mix is poured. The size of the form determines the size of the flue. Cast-In-Place liners strengthen and insulate the chimney in one process, while providing a new flue.
Aluminum - Masonry chimneys may also be lined with aluminum liners. Aluminum liners should only be used to vent certain gas fired appliances. Aluminum liners are not suitable to vent gas logs installed in woodburning fireplaces.
If you are considering having a new liner installed in your chimney, consult with an experienced installer about the best type of liner for your particular needs.
Mortar crown - The mortar crown is the concrete pad at the top of the chimney. Its purpose is to shed water and prevent it from entering the chimney chase. A proper mortar crown will overhang the edges of the chimney by an inch or more to prevent water from running down the sides of the chimney. If your mortar crown is cracked or damaged, your local chimney sweep can probably repair it for you.
Factory Built Systems
Repairing factory built fireplaces and chimneys is a lot like repairing automobiles. Just as you can't substitute car parts from one manufacturer to another, you can't substitute fireplace parts from one manufacturer to another. This sometimes poses a problem if the manufacturer of your factory built system has gone out of business. It is very important to use only the recommended parts for a factory built system. Something as seemingly insignificant as substituting a different set of glass doors can have a serious effect on the overall operation and safety of the system.
Before replacement parts can be ordered, the manufacturer and model number of the factory built system must be identified. There is usually a nameplate on the unit somewhere, but if the nameplate is located in the firebox it may become unreadable after a few years. You may have an owner's manual that will contain the required information. The owner’s manual is an important reference and should be kept as long as you own the fireplace. Often your local chimney sweep will be able to identify the unit for you and also locate and install the needed parts. | 
