$25–$50 (for replacing a single tile, not entire liner)
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What you'll need:
TOOLS
Masonry hammer
Trowel
Ladder
Safety harness
SUPPLIES
Clay or terracotta tile
Mortar
For a chimney to be in proper working order, the chimney liner or flue must also be in good shape. A chimney flue is the path through which gases and fumes from a fireplace, furnace, or wood stove exit the house. A cracked or otherwise damaged chimney flue is bad news because it can allow toxic gases to seep into your house. Here’s how to repair a chimney flue crack to ensure the safe use of your fire-powered household appliance.
Prepping to Repair a Cracked Chimney Flue
Older chimney flues are made of clay or terracotta tiles that will crack and break over time. How you’ll set out to fix a cracked chimney flue will depend on the extent of the damage. If it is indeed a tiny fix, an experienced DIYer might want to attempt it (with a partner for safety). But given that a malfunctioning chimney flue can lead to grave danger down the road, it’s better to call a chimney repair professional and hire them to fix the cracked flue instead.
Safely Climb to the Roof
You will need a ladder and a safety harness to secure your trip to the roof to access the top of the chimney. Ideally, you’ll want a partner around to spot you as you ascend and be ready on the ground for any further assistance.
Aside from making the actual climb to the top, you’ll want to feel comfortable standing on the roof by your chimney to do this work. If you have a steeply shaped roof or have any misgivings about spending some time high above the ground for however long it will take to repair the chimney flue crack, then call a chimney repair professional who has done the job safely countless times.
Inspect for Damaged or Spalling Tiles
Clay chimney flue tiles are typically two-foot squares. The tiles located at the top of the chimney are often the ones to fail first during your flue’s lifetime. This is good news because these are the only tiles you’ll likely be able to reach as a DIYer; remember that chimney professionals have all the specialized tools and techniques needed to inspect further into the flue.
Flue tiles can crack due to weather conditions and your home settling over the years. Spalling could be to blame if the tiles aren’t cracked but look pitted or otherwise rough in texture. Condensation causes spalling, so you’ll usually see evidence of spalling tiles at the top of your chimney where moisture collects.
Call a chimney repair professional if you suspect there are more than one or two cracked tiles or if the damaged tiles are too far out of reach to repair safely. At this point, it might be better to install a completely new liner rather than simply make repairs.
Inspect for Eroded Mortar Joints
Sometimes, it’s not cracked tiles causing the trouble but rather old mortar joints that are the culprit. Mortar joints can erode over the years due to moisture and heat, leaving gaps between the clay tiles in your chimney flue. Without mortar to keep them in place, those tiles will eventually loosen. If this is the case in your chimney, you must contact a pro to have them refilled.
Typically, the process involves applying fresh mortar to the entire chimney. Then, a foam plug the size of your chimney’s interior is attached to a winch and pulled up through it, spreading the mortar into the joints, where it will dry and harden.
Remove the Cracked Tile
Photo: P A Thompson / The Image Bank / Getty Images
Gently bang the cracked flue tile with the masonry hammer. It should only take a few direct strikes to crack it off entirely, allowing you to reach in to pull out the pieces. If any fall down the chimney instead, you can retrieve and discard them later.
Install a Fresh Tile
Apply mortar to the back of the new tile and press it into place where the old tile was previously. Add more mortar to the joints surrounding the tile to secure it, then scrape off extra.
Let the Mortar Dry
Photo: Jenny Dettrick / Moment / Getty Images
Carefully descend the ladder and allow the fresh mortar time to dry, per the manufacturer’s guidelines.
DIY vs. Hiring a Pro
Now that you understand the importance of a properly working chimney flue, you’ll realize that it’s even more important to ensure you fix it correctly the first time. If you are unsure of your DIY skills, call a chimney repair professional to do the work. This will save you time and ensure your safety. Remember, these pros have climbed countless roofs in their careers, so they know how to do the job safely and as quickly as possible.
If it will take more than just replacing a cracked tile, it might be time to install a new liner. The cost of a new chimney flue liner is $2,500 on average. A new liner can last between 15 and 20 years, especially the long-lasting stainless steel ones that are often installed.
While it won’t be a visible improvement to your home, a new chimney flue liner will give you and any potential buyers peace of mind that the fireplace, wood stove, or furnace can be used without the risk of toxic gases seeping inside the house.
Frequently Asked Questions
You can, but you shouldn’t. While you can still start a fire in your fireplace, the smoke and other fumes won’t have a proper way to escape if the flue is cracked. By continuing to operate your fireplace, wood stove, or furnace, you are putting your home at risk of absorbing toxic byproducts of the fire source.
A chimney flue liner can last between 15 and 20 years with proper maintenance and regular cleaning. If you’ve been in your house for longer than this period and haven’t replaced your flue liner, it’s a good idea to do so to keep your house safe and up to code.
No. Removing the cause of concern will only lead to deeper concern. You cannot use any fire-powered appliance like a fireplace or furnace without an escape route for the smoke and fumes. If you remove the flue intending to repair or replace it, you should only use the fireplace, wood stove, or furnace once the flue is in working order. If you cannot replace the flue you have removed, call a chimney repair professional immediately.
Barbara Bellesi Zito is a freelance writer from Staten Island, NY, covering real estate investing and home improvement for Millionacres, Apartment Therapy, and others.
Barbara Bellesi Zito is a freelance writer from Staten Island, NY, covering real estate investing and home improvement for Millionacres, Apartment Therapy, and others.
The homeowners guide to Chimney Repair
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