Chimney Efflorescence: The White Residue on Your Chimney

Woman with Question about Chimney EfflorescenceIf you’ve ever noticed a white residue accumulating on your brick chimney, you may not have thought much about it. However, this white staining, called chimney efflorescence, can become very problematic if left unchecked.

What Causes Chimney Efflorescence?

Efflorescence accumulates on a masonry structure as a result of moisture passing through the chimney, dissolving the soluble salts that are naturally within the brickwork and mortar. The salty liquid then evaporates when exposed to the atmosphere and leaves the salt residue on the exterior of the chimney.

Chimney efflorescence often occurs when gas appliances, such as furnaces and water heaters, are used and vented into masonry chimneys. It is also seen with high efficiency oil furnaces. When an old furnace is replaced with a more efficient one, the flu size should be reduced. If it is not reduced, it will enhance or increase the level of condensation inside the chimney. A high efficiency furnace has a lower stack temperature going into the chimney which means that the products of combustion, or the exhaust flue gases, are at a lower temperature and closer to dew point, when the condensation occurs.

Remember, we do not want any moisture inside our chimney!

We normally see chimney efflorescence appear approximately seven years after upgrading to a more efficient furnace that uses the same size chimney.

So, we have Salt on a Masonry Structure, Now What?

Do you put salt on the ice on your sidewalk or driveway? If so, you may notice that it destroys the concrete over time. The salt attacks the cement which holds the sand and aggregate particles together to form a hard surface. This is exactly what happens to your concrete or masonry chimney when it’s covered in salt, or chimney efflorescence. With a chimney, the mortar joints expand and start to push out of the chimney and also slightly move the brickwork.

To fix the problem, you will need to call a professional chimney repair company to tuckpoint the chimney and move the mortar back where it belongs. This is a labor-intensive process and unless the entire structure is re-done, the new work will not match the older bricks of the chimney.

Often, the underlying problem is the condensation level inside the chimney. Efflorescence is caused by a combination an excessive amount of condensation within the chimney and a leaky flu liner that allows the moisture to pass through the structure. To keep the condensation from happening in the first place, you will need to have a professional install a properly sized chimney liner appropriate for the class of service.

Contact Doctor Flue Today

If you’ve noticed chimney efflorescence on your structure, contact Doctor Flue today. Our team of experts will inspect your chimney for structural damage and propose a solution that works best for you, whether that be chimney repair, chimney relining, or both. Give us a call at 800-438-3583, send us an email at, or request an appointment online. We look forward to answering your questions!

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