Brick spalling is one of the most common and most misunderstood masonry problems in the Chicagoland area. When the face of a brick cracks, flakes, or pops off, homeowners often assume the brick itself was defective. In most cases, the brick was fine. Something else - water, wrong mortar, or deferred maintenance - created the conditions for the brick to fail. Understanding what causes spalling is the first step toward preventing it and saving thousands in repair costs.
What Is Brick Spalling?
Spalling is the deterioration of a brick’s surface layer. It ranges from minor surface flaking (where thin layers peel away) to deep fracturing where large chunks of the brick face break off, exposing the softer interior core. Once the hard-fired outer surface is compromised, deterioration accelerates rapidly because the porous inner brick absorbs water at a much higher rate.
The term comes from the German word “spalten,” meaning to split. In masonry, it describes any surface failure where the face of the brick separates from the body. Mild spalling is cosmetic. Severe spalling is structural - it weakens the wall, allows massive water infiltration, and if left long enough, can compromise the load-bearing capacity of the masonry.
The Science: Freeze-Thaw and Hydraulic Pressure
The primary mechanism behind brick spalling in Illinois is freeze-thaw cycling, and understanding the physics explains why certain walls fail while others on the same house remain intact.
How Water Destroys Brick From the Inside
All brick is porous to some degree. Modern fired brick typically absorbs between 5% and 12% of its weight in water (measured by the ASTM C67 Initial Rate of Absorption test). When water enters brick through cracks, failed mortar joints, or the brick surface itself, it fills microscopic pore networks within the clay body.
When temperature drops below 32 degrees F, that water begins to freeze. Water expands approximately 9% in volume when it becomes ice. In confined pore spaces, this expansion generates hydraulic pressure that can exceed 2,000 PSI - far more than the tensile strength of most brick (typically 200 to 500 PSI).
The first freeze cycle may cause invisible micro-cracking. The second cycle pushes those cracks slightly wider. Each subsequent cycle admits more water and expands the damage zone. After 5 to 10 winter seasons of this progression, the surface layer separates from the body and you see visible spalling.
Why Illinois Is Especially Destructive
The Chicagoland area experiences 80 to 100 freeze-thaw cycles per winter. Each cycle is a small stress event. Brick that would last 100 years in Georgia might show spalling after 30 years in Lake County. Homes on the North Shore - Winnetka, Glencoe, Wilmette - face additional moisture load from Lake Michigan, compounding the cycle count with higher saturation levels.
North-facing and east-facing walls are the most vulnerable because they receive less direct sunlight, stay wetter longer, and experience more freeze events than south-facing walls that warm and dry faster.
The Wrong Mortar Problem
After freeze-thaw, the second most common cause of brick spalling is incorrect mortar selection during previous tuckpointing or repair work. This is a problem we encounter on at least 20% of the homes we inspect.
How Mortar Causes Brick to Fail
Mortar is engineered to be a sacrificial element in a masonry wall. It is supposed to be softer than the brick it surrounds. When thermal expansion, moisture cycling, or minor settlement creates stress in the wall, the mortar absorbs that stress - it cracks instead of the brick.
When a contractor uses mortar that is harder than the brick, the stress equation reverses. The mortar transfers force into the brick, and the brick cracks. This is especially damaging at the mortar-brick interface, where shear forces concentrate. The result is spalling that appears right at the joint line - the brick face pops off in a strip along the mortar joint.
Type S on Residential Walls: A Common Mistake
Type S mortar (approximately 1,800 PSI compressive strength) is designed for below-grade applications, retaining walls, and areas subject to lateral pressure. It is frequently misapplied on above-grade residential walls where Type N (approximately 750 PSI) is the correct choice.
The error is understandable but costly. Contractors who primarily do new construction often default to Type S because it sets faster, achieves higher bond strength, and feels “stronger.” On a new wall with new brick, the mismatch may not manifest for years. On a tuckpointing job where the existing brick is already 50 to 100 years old and somewhat weathered, using Type S mortar can cause visible spalling within 2 to 5 years.
Portland Cement on Pre-1920 Homes
Historic homes built before 1920 typically used lime-based mortar with little or no Portland cement. This mortar is intentionally soft (often below 300 PSI). When modern Portland cement mortar (even Type N) is used to repoint these joints, the hardness differential is extreme. The old, soft brick cannot absorb the stress, and spalling follows.
Proper historic restoration requires lime mortar or a lime-dominant blend formulated to match the original mortar’s hardness and flexibility.
How to Identify Brick Spalling Early
Catching spalling early is the difference between a targeted brick repair and a full wall rebuild. Here is what to look for, organized by severity.
Stage 1: Surface Crazing (Earliest Sign)
Fine, hairline cracks on the brick face in a network or web pattern. The cracks do not penetrate deeply. The brick surface still feels solid. This stage is often mistaken for normal aging. In Illinois, it is a warning sign that moisture is cycling through the brick and freeze-thaw damage is beginning.
Stage 2: Flaking and Peeling
Thin layers of the brick face begin to separate. You may notice small flakes of brick on the ground below the wall, especially in spring after the winter freeze-thaw season. The brick surface feels rough or uneven compared to neighboring bricks. Color may appear lighter where the fired surface has detached.
Stage 3: Face Popping
Larger pieces of the brick face break away, leaving concave depressions. The exposed interior is softer, lighter in color, and more porous. At this stage, deterioration accelerates dramatically because the protective outer surface is gone. Water absorption rates can double or triple.
Stage 4: Deep Fracturing
The brick body cracks through its full depth. Pieces can be pulled away by hand. The structural contribution of the brick is compromised. Adjacent bricks may begin to shift as the wall loses bearing surface. This stage requires brick replacement, not surface repair.
Stage 5: Structural Compromise
Multiple bricks in a localized area have failed. The wall shows visible displacement, bowing, or cracking patterns. Mortar joints around failed bricks have opened, creating water pathways that accelerate damage to neighboring bricks. Rebuilding the affected section is the only repair option.
Prevention Strategies
Preventing brick spalling is far cheaper than repairing it. Most prevention measures are maintenance tasks that cost little but must be done consistently.
1. Maintain Mortar Joints
Failed mortar joints are the primary entry point for water. Annual inspection of all mortar joints, especially on exposed elevations, and prompt tuckpointing of deteriorated sections prevents the moisture saturation that drives spalling. Do not wait until the damage is widespread - early intervention costs a fraction of delayed repair.
2. Ensure Proper Drainage
Water pooling at the base of a brick wall saturates the lowest courses. Check that grading slopes away from the foundation, downspouts discharge at least 4 feet from the wall, and no sprinkler heads are hitting the brick directly. Splash blocks and extensions are inexpensive insurance.
3. Repair Caps and Crowns
Chimney crowns, wall caps, and coping stones are the first line of defense against water entering the top of a masonry structure. A cracked chimney crown allows water to flow directly into the brick below, causing spalling from the top down. Crown repair or replacement is one of the highest-return-on-investment masonry maintenance items.
4. Verify Mortar Type Before Any Repair
Before any tuckpointing or repointing work, confirm that the mortar type is appropriate for your brick. A professional contractor will test the existing mortar hardness and select a replacement that is softer than the brick. If you are getting estimates, ask every contractor what mortar type they plan to use and why.
5. Address Flashing and Caulking
Failed flashing at rooflines, window heads, and wall penetrations allows concentrated water flow into the masonry. Inspect flashing at least annually and replace any sections that are lifted, rusted, or separated from the wall.
6. Do Not Apply Sealers Without Expert Advice
Brick sealers are a double-edged sword. Film-forming sealers can trap moisture inside the brick, actually increasing spalling risk. Breathable silane or siloxane-based water repellents can help in some situations, but they are not universally appropriate. On historic or very porous brick, sealers can cause more harm than good. Consult with a masonry professional before applying any sealer product.
Repair Options for Spalled Brick
When prevention was not enough and spalling has already occurred, the repair approach depends on the severity and extent of the damage.
Localized Brick Replacement (Stages 2-4)
Individual spalled bricks can be cut out and replaced with matching brick. The key challenge is sourcing period-appropriate brick that matches the size, color, texture, and firing characteristics of the original. For homes in Libertyville, Northbrook, and surrounding communities, we maintain a salvage inventory of vintage Chicago common brick and pressed brick from demolished structures of similar vintage.
Section Rebuild (Stage 4-5)
When spalling has affected a contiguous area, individual replacement becomes impractical. The damaged section is dismantled course by course and rebuilt with matching brick and appropriate mortar. Proper bonding to the remaining wall is critical to maintain structural continuity.
Full Elevation Rebuild
In severe cases where an entire wall face has failed, the wall may need to be taken down to sound material and rebuilt. This is the most expensive outcome and the one that consistent maintenance prevents.
Patching (Limited Use)
Composite patching products exist for filling minor surface defects. They are a cosmetic stopgap, not a structural repair. Patching makes sense on isolated, shallow damage on otherwise sound brick. It is not a substitute for brick replacement when spalling is active and progressive.
Take Action Before Winter
If you have noticed any signs of brick spalling on your home, the worst thing to do is wait through another winter. Each freeze-thaw season pushes the damage further, and repair costs increase with every year of delay.
Delta Masonry & Tuckpointing has been repairing and preventing brick spalling across Chicagoland since 1987. We have completed over 2,800 masonry projects and we understand the specific challenges that Illinois weather creates for brick homes.
Call (847) 713-1648 or contact us online for a free inspection. We will assess the condition of your brick, identify the cause of the spalling, and provide a written estimate for the correct repair - not a band-aid, not an upsell, the right fix for your specific situation.