Cleaning the fireplace chimney

Posted10/3/2020 6:00 AM

Q: I use my efficient wood-burning fireplace often. The chimney has never been cleaned and the exterior is weathered. Is having it cleaned really important and what tasks can I do myself?

A: There are some maintenance items you can do yourself, but you must first have the chimney flue professionally cleaned by a chimney sweep. A cleaning also includes a complete inspection. Every year thousands of houses burn to the ground from chimney fires.


The bad outdoor spots on the chimney should be checked, but are not as serious as issues inside the chimney. The most common problem is creosote deposits from too little combustion air or burning too much unseasoned firewood. Creosote is extremely flammable when it gets hot inside the chimney.

Many homes have small chimney fires from creosote buildup and the homeowners are not aware of it. If you have ever noticed a sudden increase in the fireplace draft, this is a sign of a chimney fire. The heat from the creosote burning creates the strong draft.

When there is a creosote fire in the chimney, even a small fire, it can damage the mortar and break some tiles. If cracked tiles fall across the flue and block the air, this causes heavy smoke back drafting. You will definitely notice this if it happens.

A more serious problem is the slow deterioration of the mortar between the chimney tiles from repeated smaller fires. This can allow the fire itself or just the intense heat to penetrate the chimney and start the wall framing on fire. Wall framing may be burning for quite a while before you notice it. If you are sleeping and don't have smoke detectors, this can be catastrophic.

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Another sign that there is creosote buildup and there have been some chimney fires is puffy black pieces that fall into the fireplace. Creosote is a hard material when cold, but when it burns, it puffs up and feels somewhat like chunks of black polystyrene foam. It crumbles very easily when it is touched.

When the chimney sweep runs brushes up and down inside the chimney, it will definitely knock the puffed creosote loose if there has been a fire. When the cleaning is done, the entire length of the chimney is inspected with a small video camera. Each mortar joint and tile can be carefully checked this way.

Before hiring a chimney sweep, ask if he will do a camera inspection that you can watch. If the chimney sweep immediately suggests you need a new chimney liner without doing a camera inspection, be skeptical. Installing a new chimney liner, especially with some of the newer techniques, can cost thousands of dollars.

Once the chimney is professionally cleaned and no internal problems were found, exterior and cosmetic problems are easy to repair yourself. Professional chimney repair products are available in smaller quantities for do-it-yourself use. When working on a roof or high on a ladder, always make sure to wear a harness that is secured to the structure and have a helper support the ladder.


You may think that brick and mortar are very hard, but they are permeable to water. Over years of exposure, outdoor moisture can penetrate and deteriorate the mortar as you have noticed on some posts. This is most common in regions with many freeze/thaw cycles over winter.

Using a chisel and hammer, tap on the suspected bad mortar spots. It will come loose easily if it is bad. Fill the pits with special plastic-based mortar repair compound which matches the color of most mortar. Next spray or brush the entire chimney exterior with liquid water repellent.

When there is deteriorated mortar, the chimney crown likely also has problems. This is the top through which the flue passes. As with the mortar, chip away the bad crown spots and fill them with compound. Finish by coating the entire crown with a thin layer of compound. Special compounds that cure below freezing temperatures are available for winter application.

While up there, check the condition of the metal flashing between the chimney and the roof. Unless it is severely rusted, which requires replacement, coat the joints with flashing compound and paint the flashing.

Q: I added a room to my house. It is efficient with thick batt attic insulation and some extra is left over. Is it important to have the same insulation level in the attic over the existing rooms too?

A: It is not critical to have the same insulation across the entire attic floor. More insulation is always better though. Even if you cannot cover the entire attic floor over the existing rooms, cover as much of it as you can with the extra.

Unfaced batt insulation is best to use for the second layer. If the leftover batt insulation has a vapor barrier, cut slits in it with a knife. Otherwise, it can trap moisture between the old and new insulation layers.

• Write to James Dulley at 6906 Royalgreen Drive, Cincinnati, OH 45244 or visit

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