Cracked Chimney Flue: How to Spot One and Fix It

While most of the attention gets directed toward a firebox on a home fireplace, the chimney is just as, if not more important. You need a chimney to operate in full working order not only to maximize heat but also to keep your household safe.

cracked chimney flue liner

A cracked chimney flue is not an unusual problem. However, it’s a serious issue and one that you should resolve as soon as possible.

The question is how do you spot a cracked chimney and flue? How do you make the necessary repairs?

Understanding Chimney Flues

stainless steel chimney flue liner

A chimney flue consists of a duct, pipe, or opening in a chimney. It’s designed to extract harmful gases from a fireplace. The flue is sometimes referred to as the chimney itself. It is also regarded as the type of ventilation.

Older fireplaces are beautiful and an important part of a home yet pose additional safety risks. Most masonry fireplaces are constructed with clay liners in the chimney flue. Over time the weather conditions and the intense heat created inside the fireplace wears on the clay liners. The end result is a cracked chimney flue.

It’s imperative that you inspect a chimney flue regularly. Why? A cracked chimney liner is a serious threat to you and your family. It can not only emit harmful gases like carbon monoxide into the interior of your home, but also cause a chimney fire.

Therefore, building codes make it mandatory to have a chimney flue inspected at least once a year to prevent such a tragedy.

How to Inspect a Chimney Flue

While it’s mandatory that U.S. homes with a fireplace and chimney get inspected annually you can sometimes self-diagnose a cracked chimney flue. If you just bought a home or it’s been awhile, considering doing a quick visual check.

In order to get a better perspective, you’ll need to access the roof. If you have a steep roof or are uncomfortable with heights considering hiring a professional.

Deteriorated or missing mortar joints are the most obvious visual signs that indicate the chimney is compromised. Bad mortar joints should be dealt with as soon as possible. Once the joint begins to deteriorate it doesn’t take long for the damage to multiply.

It is impossible for clay liners to hold up forever with such drastic temperature shifts. The intense heat produced inside the chimney during a fire inside the home contributes to wear as well as elements from the outside (rain, snow, etc).

Water that freezes and thaws in a small crack of the chimney quickly accelerates into a larger crack. Once the crack becomes too extreme the mortar begins to crumble. If it gets too severe the entire chimney might collapse causing damage to the rest of the roof and interior of the home.

Unfortunately, chimneys have a lot of problems and not all of them are evident to the untrained eye. It’s mandatory that a chimney flue gets inspected by a professional once a year.

It may seem like a hassle but chimney inspections have your best interest in mind. Not only can it prevent extremely costly repairs down the road, but it also reduces fire hazards and potential exposure to harmful gases like carbon monoxide.

Places on the Chimney Liner to Inspect

It is a good idea to inspect the entire chimney. A homeowner can examine the parts at the bottom and top of the chimney that are visible without entering the unit directly. A professional can take care of the rest.

While cracked, damaged, or missing titles can occur anywhere in the chimney, there are three common places it happens:

  • Mortar Joints: The mortar joints between each section of clay tile erodes over time. It causes larger caps between the tiles where heat and harmful emissions can enter the house instead of escaping out the top.
  • Clay Tiles: Most older fireplaces were built with clay tiles in the flue. However, clay tiles are susceptible to breaking or cracking. Weather is a common contributor. Sometimes it boils down to poor construction. Regardless, over the years clay tiles wear and fall apart.
  • Spalling: Spalling happens when moisture or corrosive chemicals influence the inside clay lining to flake apart from the inside, out. As a result, the lining looks rough or pitted. It’s supposed to look smooth and flat in contrast. Spalling is notorious near the top of the chimney because it’s where condensation occurs.

How to Fix a Cracked Chimney Flue

a skilled worker fixing a cracked chimney flue liner

In the last few decades clay liners have slowly been replaced by stainless steel. Stainless steel chimney liners are preferred by builders and homeowners for several reasons.

Stainless steel chimney liners are placed down the entire length of the flue. The purpose of the liner is to seal the chimney. It acts as a barrier between the heat (and harmful emissions) and the rest of the structure.

There are other methods to repair a cracked chimney flue:

Repairing Clay Tiles

Though a short-term fix for likely a long-term problem you can sometimes address the issue by making quick, affordable repairs.

Clay tiles located near the top of the chimney generally are the first ones to fall apart because the tiles are exposed to the most drastic temperature changes. Therefore, not only is it a good place to start your own inspection (if you’re comfortable on the roof), but also a place that you can quickly repair.

Since you won’t be able to go down too far into the chimney, check the first couple of rows at the top of the chimney. If you notice any cracks then try replacing the clay tile with a brand new one. You can also add mortar to the joints while you’re at it.

Repairing clay tiles from the top of the chimney is a DIY repair so long as you’re comfortable climbing ladders and standing on a roof. If not, it’s very wise to hire a professional to make the repairs.

Cast-in-Place Liners

Cast-in-place liners are a good alternative if the problem is a lot larger than merely replacing a few clay tiles at the top of the chimney flue.

The process works by having a professional create a new flue by placing a mold inside the existing chimney. It essentially acts as a new liner surface that sits on top of the existing one. Cement is pumped around the liner to secure it.

Cast-in-place liners are not a DIY repair and do cost a substantial amount of money. However, it will allow you to start using the fireplace once again.

Stainless Steel Liners 

If you want to do the job right then stainless steel liners are the way to go to fix a cracked chimney flue. Stainless steel liners are gaining in popularity and for good reason.

Stainless steel liners are available in a variety of shapes and sizes. The versatility of the liner is exceptional. The type of liner can bend and accommodate the existing shape of a chimney that’s likely offset after decades of wear and tear. Consequently, it’s a more effective repair compared to cast-in-place liners.

Stainless steel liners in chimneys also hold up better because flexible liners expand and contract. It prevents buildup from sticking to the liner and instead flaking away. Therefore, creosote buildups should not accumulate near as quickly.

Hire Chimney Inspectors for Repairs

chimney inspector

It is important to hire a professional to inspect your chimney at least once a year and delay using the fireplace until a cracked chimney flue is repaired. A clean, properly functioning chimney flue not only performs better but also keeps you and your family safe.

At Early Times, we are diligent and careful to exceed the expectations for all of our customers. We understand the danger of creosote buildup and the spread of chimney fires so it’s better to get your chimney inspected. We fix all the chimney problems such as a cracked chimney flue or a cracked mortar so you can safely use your chimney. Speak to a specialist and get a free quote online today.

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