Spalling: An Explainer


Constant water penetration into the bricks and mortar joints can lead to spalling.

Constant water penetration into the bricks and mortar joints can lead to spalling. Waterproofing the masonry can prevent this.

What exactly is spalling, and how does it impact your chimney? Spalling is the flaking off of a brick surface and is evident when the face of the masonry is missing. Pieces of brick(s) may be found on the ground, in your gutters or on your roof, which is an indication that there is a problem that needs to be addressed. Chimney spalling is a sign of severe moisture penetration of your masonry bricks.

How is spalling caused?

Spalling is caused when the masonry absorbs too much moisture and is subjected to freeze/thaw cycles. Damages can be worsened by condensation of flue gases in improperly-sized flue liners and gaps or cracks in mortar joints on the inside of your chimney, as well as by moisture entering the interior of your chimney via a crack in your chimney’s crown.

Softer types of bricks are more susceptible to moisture penetration than hard type bricks. Unfortunately, builders often opt to use softer type bricks because they are the lesser expensive of the available options. If you find yourself having to rebuild your chimney because the brickwork is beyond repair, request that hard bricks be used to ensure that your completed project lasts longer.

Why is my chimney masonry worse off than masonry on other parts of my house?

Chimneys usually show damage more than other parts of your home because they are more exposed. As you might expect, the top portion of your chimney will show the first signs of moisture intrusion issues. By the time bricks spall, the damage has already been done. These bricks cannot be repaired and, instead, must be replaced.

It may be tempting to cut a few corners in an attempt to save money and replace only a few spalled bricks or only do a partial rebuild of your chimney; keep in mind, however, that your entire chimney will need to be rebuilt at some point, and, as such, any partial repair will only be a temporary fix. You can put makeup on a pig, but it’s still going to be a pig.

How can I prevent my newly-repaired brickwork from spalling again?

In an attempt to stop further moisture penetration, many homeowners will opt to have a masonry water repellent applied, but bricks that already have interior damage will continue to spall.

If chimney spalling has become an issue for you, the time for repairs is now! At Ace Chimney Sweeps, we know how important your family’s safety is, and how dedicated you are to protecting your investment. That’s why we make the safety and efficiency of your chimney, fireplace, air duct system and dryer vent system our priority. Let us put our over twenty years of experience to work for you. Give us a call today!