Why flue tiles crack and how to repair them

Dec 21, 2023

No matter whether your chimney vents a fireplace, wood stove or furnace, it likely contains a section of terra cotta flue tiles linked together to form the chimney lining.

This flue liner should be well sealed to protect the efficiency and soundness of your chimney. But over time and usage, problems and defects can develop that threaten the safety of your chimney. Cracked flue tiles are one of the most common problems homeowners deal with.

Cracked flue tiles

Cracked tiles frequently occur when the heat is not evenly distributed throughout the chimney. This causes the tiles to expand in an uneven fashion and the result can be cracking, buckling or splitting. Terra cotta tiles are most likely to have this problem because the material does not quickly absorb heat.

Flue tiles can also crack due to sudden events such as a chimney fire, earthquake or even lightning strike. Inferior craftsmanship of the chimney, or even the ongoing settling of your home, can also cause cracked flue tiles.

Finally, exposure to corrosive chemicals and moisture can cause pieces of the flue liner to delaminate. This process is known as spalling.

Why cracked flue tiles are dangerous

Cracked flue tiles can lead to gas leakage that allows carbon monoxide to seep into your homes interior.

Combustible creosote or soot can escape through the openings in the cracks and gaps and build up outside of the flue liner. If the creosote catches fire in your chimney, very serious damage to your home can occur because the fire will no longer be restricted to the flue.

Pieces of flue tile that break off due to spalling can then form dangerous blockages within your chimney.

Loss of chimney efficiency

The defects caused by cracked flue tiles, gaps, and spalling can begin a process that not only threatens your family’s wellbeing, it can begin destroying your chimney from the inside out.

In order to work efficiently, chimneys must be free of gaps and cracks so that gases cant escape. Chimneys are like straws. If a straw has a crack or hole in it, liquid wont flow through it properly.

Cracks and gaps allow extra air into your chimney. They also slow the flow of smoke and gases rising up and out. As a result, your fireplace, wood stove or furnace will diminish in heat-efficiency.

How to fix cracked chimney tiles

The terra cotta flue tiles themselves cannot be repaired due to the expansion and contraction properties that occur in a flue when burning fires. The expansion stress will cause any repair to crack again.

The best way to fix cracked tiles is by lining or relining the chimney itself.

Typically, the preferred option for a chimney liner is a stainless steel liner. Stainless steel comes with a lifetime warranty and usually never needs replacing.

Another alternative is removing the chimney stack and rebuilding it with new terra cotta flue tiles, but this is a more costly route.

If you have concerns about cracked flue tiles, don’t hesitate to reach out to Chimney Clean Company.

Smoking back

There are many fireplaces that seem to smoke back into the house no matter what is done. In our experience, the most common cause is that the fireplace simply needs to be cleaned. This is especially likely if the fireplace has gotten worse over time, that is, the smoking back is worse now than it used to be.

Several other possible causes of smoking back are problems with the damper, chimney cap, grate, firewood, or structural problems with the chimney itself. At Chimney Clean Company, we do a full inspection with every cleaning, or we can also do just the inspection if the chimney doesn’t need to be cleaned. This inspection is designed to reveal any causes of smoking back.

Broken chimneys

In the Bay Area, many chimneys were broken in the 1989 Loma Prieta earthquake. Usually, these chimneys are broken at or near the roof line, although sometimes they can be broken further down, even at the ground level.

We are fully licensed masonry contractors. We rebuild broken chimneys. If they are broken at the roof line, this usually entails taking the chimney part of the way down brick by brick, installing steel reinforcing bars, getting an inspection from a city inspector, then rebuilding the chimney back up around the steel rebar.

Missing mortar or damaged bricks

Over time, many chimneys develop places that are missing mortar between bricks, or damaged bricks, either inside the firebox or on the outside of the chimney. These areas can usually be repaired, either by replacing the missing mortar or replacing the bricks themselves. Items such as these can be dangerous because they can allow flames, sparks or hot gases to enter the structure of the house.

Water entry

Sometimes the metal that seals the chimney at the roof, called “flashing”, will come loose or develop leaks. In this case, water sometimes comes into the ceiling of the room and causes water spots and stains on the sheet rock. This flashing should be repaired before the water causes more damage.