Q: We bought a Queen Anne Victorian 10 years ago, but have never used the chimneys because the chimney sweep said pigeons had been pecking at the mortar. There is no chimney liner. I have been up on the roof and see where some of the mortar is missing, and think I could easily fix that. I tore out the plaster on the first floor covering the chimney, thinking I might just be able to repair it from the outside, but it all looks pretty good.

Q: We bought a Queen Anne Victorian 10 years ago, but have never used the chimneys because the chimney sweep said pigeons had been pecking at the mortar. There is no chimney liner. I have been up on the roof and see where some of the mortar is missing, and think I could easily fix that. I tore out the plaster on the first floor covering the chimney, thinking I might just be able to repair it from the outside, but it all looks pretty good.

We don’t have a lot of money, so I usually try to do things myself. I read somewhere that there was a special high-heat mortar that should be used, but I haven’t found a source for it. What would you suggest to make the chimney usable?

A: The heyday of the Queen Anne was the 1890s. It’s an architectural style characterized by pediments and porticos, dentil moldings and plenty of fancy trim known as gingerbread.

In those days, heat was provided by coal. Your fireplace is probably one of several "coal heaters" gracing your home. The firebox is shallow and the flue is narrow. Today, coal heating is out, but the firebox should support a small wood fire.

We’re not surprised that your fireplace is equipped with an unlined masonry chimney. Widespread use of flue liners did not occur until a couple of decades after the turn of the century. To make the chimney usable, we think you should get it inspected by a reputable chimney sweep and be prepared to bite the bullet and get a flue liner.

Pigeons pecking at the mortar is not a big problem. Unless these are real strange birds, the damage they’ve done is to the chimney cap or to the outside of the chimney. Your much larger problem could be on the inside of the chimney. While it’s a simple matter to repoint the exterior brick, failed mortar on the inside of the chimney is a fire hazard.

Because of the age of the fireplace, it is more likely than not that heat and flue gases from more than a century of fires have played havoc with the brick and mortar. Think of a flue liner as an investment in your safety or as a reasonably priced fire insurance policy.

A flue liner in a masonry chimney is essentially a clay, ceramic or metal tube installed inside of the chimney, intended to contain the combustion products, direct them to the outside atmosphere and protect the chimney walls from heat and corrosion.

Flue gases are acidic and eat away at the mortar joints from inside the chimney. Failed mortar joints can result in serious safety hazards, as well as result in a reduction in the useful life of the chimney. As the mortar joints erode, heat transfers more rapidly to the nearby combustibles, creating a fire hazard, and dangerous gases such as carbon monoxide can leak into the living areas of the home.

Fire is more likely if there is creosote buildup inside of the chimney. Creosote is a sticky, flammable byproduct produced by burning unseasoned soft woods such as pine and Douglas fir. It coats the walls of the chimney and saturates the mortar. If the creosote is ignited in the chimney, it’s possible that the flames will migrate from the flue to the framing, causing catastrophic damage.

There are three types of flue liners. The most common material used is clay tile. They are installed in sections and mortared together. The weak link of this system is the mortar joints. Another potential defect is that clay tile does not rapidly absorb heat or evenly distribute it, so it is subject to cracking.

Metal flue liners made from stainless steel are primarily used to upgrade and repair existing chimneys. These liner systems are tested and listed by the Underwriters Laboratories and, if properly installed and maintained (a yearly cleaning), are safe and durable.

Finally, cast-in-place chimney liners are lightweight, concretelike products that are poured and formed inside a chimney. One method of installation is to pour heat-resistant concrete down a chimney and drag a form shaped like a metal bell up and out, forming a smooth, seamless, insulated passageway for flue gases to be vented to the outside. As an added bonus, this type of liner improves the structural integrity to aging chimneys.

For more information, we recommend the Web site of the Chimney Safety Institute of America at www.csia.org.

***

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