What To Do About Spalling

Advisory Report - November 2000

What To Do About Spalling
Spalling. Most people have never heard of it before. But there's a good chance that you've witnessed it on your home or on someone else's home. 

The faces on bricks sometimes peel off due to water being absorbed by the bricks and then freezing. The expansion of the ice will break off the brick's face if the brick has not been fired at a high enough temperature. This is called "spalling."

One of the main causes of spalling bricks near the top portion of a chimney is a defective masonry cap. Often times the cap is cracked and it allows water to enter into the brickwork below. 

The water is then absorbed by the masonry, and during cold weather it freezes. During this process, its volume expands, causing pieces of the brick face to come off. Spalling can also result from cracked and open mortar joints between the bricks. 

The only way to control the problem is to stop the water from penetrating into the chimney. Damaged areas of mortar should be removed and fresh mortar installed. Some people recommend applying a waterproofing agent, such as silicone, to the chimney to prevent or reduce water absorption. 

Learn more about brick chimneys.