Spalling Brick on a Chimney: What It Means and Why It Gets Worse

If pieces of brick are flaking off your chimney, the problem is commonly called spalling. It can begin as a rough surface or a few shallow chips and progress until the face of the brick breaks away.

For a Colorado chimney, spalling often points back to moisture exposure combined with weathering.

Why brick faces break down

Brick is porous. When water enters and is repeatedly exposed to freezing conditions, internal stress can contribute to surface deterioration. The National Park Service specifically identifies freeze-thaw action as a cause of masonry damage when water is present.

Other causes can include incompatible mortar, aggressive cleaning, trapped moisture, salts and long-term weather exposure.

Why one damaged brick matters

The hard outer surface of a brick helps protect the softer interior. Once that face is lost, the exposed core can absorb water more readily and deteriorate faster.

A few damaged bricks do not automatically mean the whole chimney must be rebuilt. But they are evidence worth investigating.

Look for the source of moisture

Before replacing brick, check why it is getting wet.

Possible causes include:

• Cracked crown
• Missing cap
• Open mortar joints
• Failed flashing
• Poor drainage at the top
• Non-breathable coatings trapping moisture

If the moisture source remains, new brick may eventually suffer the same problem.

Repointing versus brick replacement

Repointing replaces deteriorated mortar in joints while leaving sound bricks in place.

Brick replacement is needed when individual masonry units have lost too much material, cracked severely or no longer provide reliable support.

Many chimneys require a combination: replace the worst brick and repoint surrounding joints.

Why matching mortar matters

Mortar is not simply glue. It has to be compatible with the brick and the age/type of masonry. A mortar that is excessively hard relative to softer older brick can change how moisture and movement are handled.

For older chimneys, repair material selection deserves attention rather than defaulting to the strongest mix available.

What about waterproofing after repair?

A breathable, vapor-permeable water-repellent treatment may be appropriate for certain masonry after necessary repairs and drying. Non-permeable coatings can trap moisture and worsen spalling, especially if applied over damp masonry.

Waterproofing should be the finishing strategy, not the substitute for repair.

When spalling becomes urgent

Prompt evaluation is appropriate if:

• Bricks are loose
• Pieces are falling onto the roof or ground
• Large sections are deteriorating
• The chimney is leaning or bulging
• Mortar joints are deeply eroded
• The crown and upper courses are breaking apart

Falling masonry is a safety concern in addition to a maintenance issue.

Keaton Chimney Solutions provides chimney masonry repair and inspection throughout Denver, Colorado Springs, Fort Collins and nearby Colorado communities. Call 720-734-5373.

Need help with a chimney or fireplace in Colorado? Keaton Chimney Solutions serves Denver, Colorado Springs, Fort Collins, and surrounding communities. Call 720-734-5373.