Spalling damage to a clay chimmney flue tile (C) Daniel Friedman Masonry Chimney Flue Tile Damage

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Chimney clay tile flue liner damage inspection, diagnosis, repair:

This article describes how to detect and assess chimney flue tile or flue line damage and how that damage is repaired.

These articles on chimneys and chimney safety provide detailed suggestions describing how to perform a thorough visual inspection of chimneys for safety and other defects. Chimney inspection methods and chimney repair methods are also discussed.

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Damaged Chimney Flue Tiles: cause,

Improper chimney flue construction risks hidden damage (C) Daniel FriedmanFlue liners can be made of clay, ceramic or metal and must contain the products of combustion and protect the shell from heat and corrosion. Clay linings are usually square, round or rectangular sections two feet in length.

[Click to enlarge any image]

They are stacked upon each other with refractory cement in the joints to form a continuous smooth walled vent from below the appliance inlet to the top. A space of one half inch to one inch must be maintained between the flue and masonry surround. Alignment of the flue tiles is secured with one walnut sized mortar deposit between the masonry surround and each of the faces of the tile.

As the flue is heated the warm liner will expand outward and lengthwise. Thus it is important that the liner not be secured to the surrounding masonry. The air space effects a reduction of temperature at the exterior of the masonry surround and helps to maintain the elevated temperature of the flue for proper draft.

At above left is an example: an improperly-constructed chimney flue and cap that risk leaks and hidden damage to the chimney flue.

[Also see: U.S. vs. Canadian Unlined Masonry Chimney Flue Requirements & Case Study -- -Editor]

Unsafe masonry chimney liner - damaged clay flue tile liner (C) Daniel Friedman Unsafe masonry chimney liner - gaps between clay flue tile liners(C) Daniel Friedman

Damaged clay flue tiles lining a chimney are often obvious only from a rooftop inspection such as we show in these photos. At above left we see that frost has broken off a portion of the clay liner for this chimney and that fine cracks in the clay flue tiles tell us that additional damage may have occurred below.

At above right we see poor chimney construction that left misaligned chimney tiles, inviting water to leak into the chimney structure, adding to the risk of frost damage and possibly causing an unsafe flue.

Examples of Chimney Flue Tile Liner Internal Damage, Leaks, Hazards

Spalling damage to a clay chimmney flue tile (C) Daniel Friedman Chimney deterioration (C) Carson Dunlop Associates\

Damage to clay chimney flue tile liners can also appear as spalling shown in our photo (above left) or as shown in Carson Dunlop Associates [at REVIEWERS] sketch (above right). Notice that the chimney wall is getting thin at the left side of the flue. It is time to have this chimney lined for safety.

Incomplete chimney liner (C) Carson Dunlop Associates

Many water damaged chimney flues could have been prevented by installation of a good chimney rain cap and crown or top seal at the time of construction.

The sketch at left shows the effects of gaps in a chimney liner. While the drawing depicts a regular gap as if magically the upper clay flue tile was suspended curing chimney construction, this is not as impossible as it may seem. Details in the drawing show the upper liner was suspended by nails, leaving a mortar gap between the clay flue tiles.

This flue tile liner gap can also occur if sections of the flue tiles are broken and lost after chimney construction, later in its life.

These flue liner gaps may explain why white efflorescence appears mysteriously somewhere below the top of the exterior of a masonry chimney. Gaps in the chimney liner can be found by a camera inspection of the flue interior; they might be suspected based on damage or stains on the chimney exterior.

Significance of Finding Soot at the Chimney Top

Soot at a chimney top may mean very unsafe conditions (C) Daniel Friedman

Watch out: If you see soot forming at a chimney which is venting gas-fired appliances you should shut the equipment down immediately and call for an expert to inspect and correct the chimney or equipment problem. Gas fired equipment can suddenly malfunction, producing soot, and blocking a chimney.

The result is the production of dangerous, possibly fatal carbon monoxide gas. Be sure that your building has working carbon monoxide detectors (CO Gas Detectors) as well as working smoke detectors that are properly located and installed.

Soot at the top of a chimney, regardless of whether the chimney is metal or masonry, can be a clue about improper and inefficient heating system operation where oil-fired heating boilers, furnaces, or water heaters are installed.

Photo of a sooty metal chimney cap venting an oil-fired heater was provided courtesy of Roger Hankey.


Continue reading at CHIMNEY INSPECTION at ROOFTOP or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see Re-Lining Choices for Masonry Chimneys




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